Sabin Pond Comprehensive Initial Drawdown Plan Boardman River Dam Removal Project Grand Traverse County, Michigan

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2 Sabin Pond Comprehensive Initial Drawdown Plan Boardman River Dam Removal Project Grand Traverse County, Michigan Prepared for: Grand Traverse Band of Ottawa and Chippewa Indians (MACTEC Project Number: ) Prepared by: MACTEC Engineering and Consulting, Inc. Traverse City, MI June 24, 2011

3 ACKNOWLEDGEMENTS We would like to acknowledge the Grand Traverse Band of Ottawa and Chippewa Indians, the United States Fish and Wildlife Service Tribal Wildlife Grants Program and the Bureau of Indian Affairs, Circleof-Flight Program, as administrated through the Great Lakes Restoration Initiative who provided funding for the Boardman River Dams Removal Project. This document was prepared by MACTEC s Project Team that included both MACTEC and Inter-Fluve, Inc. i

4 TABLE OF CONTENTS ACKNOWLEDGEMENTS... i 1.0 INTRODUCTION DISCHARGE AND WATER LEVEL CONTROL PLAN Objectives of Sabin Initial Drawdown Summary of Initial Drawdown Considerations Existing Structure Discharge Characteristics Existing Streamflow Characteristics Hydrologic Effects of Initial Drawdown Sediment Transport and Water Quality Effects Fishery Effects Summary of Analyses and Findings for Plan Formulation Seasonal Considerations Drawdown Rates Discharge and Water Level Control Plan Schedule Drawdown Implementation Logistics Project Requirements and Criteria SEDIMENT MANAGEMENT PLAN Initial Drawdown Potential Effects Impoundment Sediments Steep Hill Slopes Adjacent Tributaries Sediment Management Recommendations during Initial Drawdown RE-VEGETATION PLAN MONITORING AND REPORTING Streamflow and Reservoir Level Erosion, Sedimentation and Water Quality Monitoring Sediment Migration Monitoring Tributary Changes Monitoring Steep Hill Slopes Fish Rescue Sabin Structure Record-Keeping Project Reporting Drawdown Plan Modifications Emergency Preparedness Photo Documentation Public Notifications and Communications REFERENCES FIGURES Figure 1-1 Figure 1-2 Figure 2-1 Figure 2-2 Figure 2-3 Figure 2-4 Sabin Pond Boardman River Watershed Sabin Outlet Facilities Boardman River Flow Duration Data at Sabin (MDEQ) Boardman River Flow Duration Data at Sabin (MDEQ) Compared to USGS Station ) Flood Discharge Frequency Data for Boardman River at Sabin Dam Based on MDEQ Flood Discharge Database ii

5 Figure 2-5 Sabin Discharge Capacity - Powerhouse and Spillway Discharges (No Culvert Discharge) Figure 2-6 Sabin Discharge Capacity - Powerhouse and Spillway Discharges (All Five Culverts Open) Figure 3-1 Inundated Area/Elevation Associations Figure 3-2 Areas of Potential Channel Incision (Water Level 607 ) Figure 3-3 Plat Map (1839 & 1853) and USGS Topographic Map (1985) Comparison APPENDICES Appendix A Appendix B Appendix C Appendix D Sabin Structure Hydraulic Information Existing Condition Streamflow Characteristics Structures Inspection Form Sediment Quality Data Summary iii

6 1.0 INTRODUCTION This Comprehensive Initial Drawdown Plan (CIDP) provides background information and several plan elements to complete an initial drawdown of Sabin Pond. It is anticipated that the Sabin Dam will be removed during 2012 and a final drawdown will be completed in conjunction with the dam removal. This CIDP includes the following elements: 1. Discharge and Water Level Control Plan (DWLCP), 2. Sediment Management Plan (SMP), 3. Re-vegetation Plan (RP), and 4. Monitoring Plan (MP). The DWLCP, SMP, and RP are inter-related, as each one influences or is influenced by the others. Sabin Pond is an approximately 38-acre (historic water level) impoundment with a maximum depth of approximately 15 feet (ft). The Boardman River drainage area at Sabin Dam is approximately 268 square miles (sq mi), although the Michigan Department of Environmental Quality (MDEQ) has estimated that only approximately 210 sq mi actually contribute surface runoff. Discharge from Sabin Pond can be made using multiple outlet facilities. The facilities include a powerhouse with two turbine bays. The original powerhouse included one turbine bay (Unit 1). A second turbine (Unit 2) was added in 1930 (Harza, 1930). The Unit 1 turbine is no longer in place, leaving the Unit 1 bay with an opening in the floor. The Unit 2 turbine is still in place. There is a principal spillway consisting of a Tainter gate and an auxiliary spillway with stop logs controlling flow over the crest. There are also five culverts under the auxiliary spillway that provide the lowest existing outlet from Sabin Pond. These spillway structures are separate structures from the powerhouse. Discharge and Water Level Control Plan The DWLCP is intended to define the general means of using the existing discharge facilities to lower and maintain the Sabin Pond (Figure 1-1) water level as low as practical until the final drawdown and dam removal occur. While historically Sabin Pond water level was held at approximately ft elevation (Grand Traverse County, 2009), the controlled water level has more recently been lowered to approximately elevation 611 ft. For purposes of this document, the present water level is assumed to be elevation 611 ft, although it varies with river flows and adjustment in stop log levels, and drawdown heights in this plan are referenced to this elevation. 1

7 It is important to note that this plan addresses the actual drawdown, during which time the Sabin Pond water level would be lowered to a new controlled (or hold-down ) water level, but also the subsequent period until the anticipated final drawdown and dam removal is implemented. While no activities of specific concern are expected to occur during that hold-down period, activities such as debris removal and erosion control must occur and conditions may be slightly different from those historically observed due to the lower water level. Concerns such as the effect of the new control level on downstream discharge rates during large runoff events are addressed. The culverts incorporated into the auxiliary spillway have wooden lift gates located at the entrance to the culverts that control flow into the culverts; these lift gates are submerged by historic pond water levels and, therefore, not visible. The gates have not been operated in recent years and the condition of the gates is not known. Additionally, if these gates are opened, they provide the ability to virtually drain Sabin Pond during low flows such as typically occur in summer months. Without use of the culverts, it is expected that drawdown of the pond level to approximately 607 ft can be achieved. With use of the culverts, a drawdown to approximately elevation ft may be accomplished. Lower pond levels increase significantly the potential for erosion of a stream channel through the length of Sabin Pond and, lacking a pool of water upstream of the dam to capture suspended sediments, conveyance of eroded pond sediments into Boardman Lake. Both the operational/physical condition of the lift gates and the sediment discharge are primary concerns for this initial drawdown. Uncertainties associated with each exist; however, and the assessment of how these will influence the initial drawdown activity will be best resolved during the drawdown when the gates can be better accessed and sediment transport conditions observed. This plan addresses the full range of possible drawdown using the existing facilities, but recognizes that the lowest drawdown levels using the culverts may not be beneficial to project goals due to lift gate conditions and/or the discharge of an excessive amount of sediment. Sediment Management Plan The initial drawdown of the Sabin impoundment is intended to be the first in a series of steps aimed at removing the dam. The initial drawdown may lower the water surface as much as 8.5 ft, from elevation 611 ft to approximately ft, utilizing the existing water control structures. It is possible, if not likely, that constraints will prevent the completion of this full drawdown and the lowest water level will be above ft. The drawdown will occur slowly, at a maximum rate of 0.5 ft per day and an average rate not exceeding 0.3 ft per day, and the effects of this drawdown within the impoundment, on sediment 2

8 transport, and on the Boardman River channel and Boardman Lake downstream of Sabin Dam will be evaluated throughout the process. Should undesirable effects be observed, the process may be halted at any point. It is important to note at the beginning that sediment is likely to be transported downstream of Sabin Dam with the maximum possible drawdown. Areas noted within and downstream of the impoundment that will change during the initial drawdown are discussed in detail in Section 3.0. The primary impoundment changes include a much decreased impoundment size and a newly-created channel cut through impounded sediment. A partial drawdown of 4 ft (to 607 ft) will result in an impoundment that extends only about 800 ft upstream of the dam. This impoundment will be small in area as well as volume, as it would cover approximately six acres would mostly be two to three ft deep. This change in impoundment dimension will decrease the storage capacity and decrease the residence time of water and associated suspended sediment. The lowering of the water elevation will result in channel formation through the impounded sediments. Channel formation may cause incision of two to four ft through the upper half of the impoundment. A full drawdown, or an additional 4.5 ft drop in water level at the dam (from 607 to ft), would likely not increase the channel incision significantly at the upstream end of the former impoundment, but would extend the incised channel to the dam and increase the incision downstream by that same amount while also eliminating any sediment trapping by a remaining pool. Re-vegetation Plan Re-vegetation of the bottomland soils exposed during the drawdown period will not be actively planted but will re-vegetate through natural recruitment and germination of the existing seed bank. These areas will be actively monitored in accordance with an Invasive Species Monitoring Plan (ISMP). If deemed necessary, certain areas will be planted with native genotypes to minimize/control the spread of invasive species. Monitoring Plan Monitoring to be performed during the initial drawdown and hold-down period includes monitoring of flows and water levels, water quality, erosion, and monitoring of equipment and structures. In addition, fish rescue, record keeping, reporting, photo documentation, and public notification are discussed. Because a drawdown to the level possible using the existing discharge facilities at Sabin would leave no pond volume upstream of the outlets to capture suspended sediment produced by channel formation, monitoring will be important to determine when the drawdown should be terminated and the level stabilized. 3

9 Section 2.0 of this document contains the primary components of the DWLCP for Sabin Pond. Section 3.0 addresses the SMP, and Section 4.0 covers the RP. The MP is provided in Section 5.0, and references are provided in Section 6.0. A series of appendices provide supporting information for the assessment of effects of implementing the CIDP and for use in the implementation of the CIDP. 4

10 2.0 DISCHARGE AND WATER LEVEL CONTROL PLAN 2.1 OBJECTIVES OF SABIN INITIAL DRAWDOWN The DWLCP defines the conditions that will be imposed on the system that will dictate certain needs for the other plans. Consequently, it is important to clearly define what is to be accomplished by the initial drawdown. The overall goal of the DWLCP is to achieve maximum drawdown of the impoundment using existing water control structures at Sabin powerhouse and spillways, consistent with other project considerations and constraints. The DWLCP defines how the water level in Sabin Pond will be controlled beginning with implementation of the initial drawdown in the summer of 2011 and extending into 2012 when the final drawdown and dam removal activities are anticipated to be implemented. This DWLCP is not intended to be an operations plan, providing mechanical details associated with the manipulation of water control structures to achieve the initial drawdown. The DWLCP provides statistical information regarding what streamflows and water levels are likely to occur during the initial drawdown period based on historic streamflow characteristics. Flows in the Boardman River downstream of Sabin Dam will be a result primarily of the natural runoff during the period, with some influence of the release of water stored in Sabin Pond to incrementally increase streamflow rates during the lowering of Sabin Pond. The storage volume in Sabin Pond is relatively small, and the incremental increase in flow due to lower the water level is small. The maximum planned water level lowering rate of 0.5 ft per day equates to approximately six cubic ft per second (cfs) and two cfs for pond levels at the beginning of the drawdown (pond level 611 ft) and at elevation 607 ft, respectively. The median (50 percent [%] exceedance) Boardman River flow at Sabin Pond during the planned drawdown period (summer) is approximately 170 cfs and the 95% exceedance flow is approximately 150 cfs. During the high runoff month of March; however, the median daily discharge rate is approximately 350 cfs and the Sabin Pond water level would be approximately 604 ft if the culverts are used or 609 ft if the culverts are not used (all flow through the turbine bays). Since the proposed schedule places the actual dam removal in 2012, the DWLCP includes a pond holddown plan to be implemented following completion of the initial drawdown. Assuming the structures will not be actively managed during high inflows to adjust discharges, the hold-down plan will involve the selection of an appropriate discharge structure setting that will function as safely as possible and not create additional risk in the event of future flood events. In the discussion below, the DWLCP refers to both the initial drawdown procedure as well as the subsequent hold-down scheme which may follow initial lowering by full drawdown. 5

11 The DWLCP includes: Consideration of: Capacity and configuration of the water control structure Condition of the operable discharge equipment (ability to be safely operated) Pond bathymetric characteristics, including storage Watershed hydrology and streamflow including seasonal characteristics Consideration of sediment trapping capacity of the remaining impoundment Recommended timing for the initial drawdown Example outlet structure settings for the indeterminate post-drawdown period that will: Pass high flows as safely as practical Provide a minimum low flow, to the extent practical, during dry periods An assessment of overall safety concerns It is assumed for this drawdown analysis that no equipment (gates, trash racks, turbines, or other equipment) will be removed. The initial drawdown of Sabin Pond is a reversible step in the overall Sabin Dam removal project (i.e., the Sabin Pond could be raised back to its previous pond elevation), as its primary purpose is to reduce the duration of the final drawdown prior to dam removal. Specifically, the objectives of the Sabin Pond initial drawdown can be summarized as follows: Use existing discharge facilities to minimize time required to lower Sabin Pond when the final drawdown is implemented (anticipated in 2012). Reduce impact magnitude of full drawdown by extending the period over which effects, such as erosion and sediment processes, will occur. Control and reduce to the extent practical, the erosion and sediment transport processes in the Boardman River, Sabin Pond, and tributaries around Sabin Pond that will be initiated by the water level lowering. 2.2 SUMMARY OF INITIAL DRAWDOWN CONSIDERATIONS This section of the DWLCP provides an overview of the considerations identified as potentially significant for the initial lowering of Sabin Pond using the existing water control structures. These include potential effects to natural resources and infrastructure. Additional discussion of the effects is provided in Section Existing Structure Discharge Characteristics Discharge rating relationships of the existing water control structures at Sabin Dam are an important consideration in drawdown plan formulation and are presented in detail in Appendix A. Characteristics of the structures at the dam available from Sabin powerhouse modifications plan drawings (Harza, 1930) 6

12 and the Sabin Dam Emergency Action Plan (Grand Traverse County, 2009) are presented in Table A-1 (Appendix A) and illustrated in Figure 2-1. The lowest constructed outlet from Sabin Pond is a set of five culverts located within the auxiliary spillway structure. These culverts are elliptical with a 60-inch span and 27-inch rise. The culverts are believed to have an upstream invert elevation of approximately ft, or approximately 5.5 ft lower than the next lowest outlet elevation, which is at the powerhouse and two turbine bays. Flow through the culverts is controlled by wooden lift gates (Grand Traverse County, 2009), the condition of which is not known; the culverts have not been used in recent years. When the tops of the culverts and wooden lift gates become visible and accessible after the water level reaches maximum drawdown without use of the culverts and the condition of the wooden lift gates can be better evaluated, an assessment will be made to determine if lift gates should be removed to allow flow through one or more of the culverts. While opening all of the culverts would allow lowering the pond level an additional five ft, doing so would virtually eliminate a pond upstream of the dam and significantly increase the depth of channel incision and the downstream extent of the channel incision. The absence of a pond would reduce the ability to prevent suspended sediment, or even bedload, from passing downstream. During a higher runoff event(s), the upstream water level might temporarily rise to form a pond due to inflow rate exceeding the discharge capacity at the lower elevations (figures A-6 and A-7 illustrate retention time as a function of discharge). However, the sediment transport resulting from lowering the water level by that amount and the virtual elimination of a pond to trap sediment would lead to significantly higher potential for discharge of sediments downstream. The sediment management plan does not include implementation of controls expected to be required for this lowest potential drawdown; rather the approach is to drawdown the Sabin Pond level and determine through monitoring when a maximum acceptable sediment discharge condition is reached and also adjust the drawdown if necessary based on potential high runoff events. The primary spillway, the Tainter gate, has been fully open during recent operations of the Sabin structure, resulting in weir flow over the gate sill. Additionally, stop logs controlling flow through the powerhouse have been lowered, resulting in a small amount of flow over the top of the stop logs and passing through the Unit 1 bay. This condition produced a water level of approximately 611 to 612 ft during normal flow periods during spring With the exception of the culverts, the lowest outlet is through the two turbine bays in the powerhouse. The Unit 1 turbine was removed, including the wicket gates and runner, leaving only an approximately 6- ft diameter opening in the floor of the bay. The sill elevation controlling inflow to the turbine bay is 7

13 approximately ft and is slightly higher than the wicket gate opening. The sill elevation at the inflow to the Unit 2 turbine bay is a similar elevation. The wicket gates for the Unit 2 turbine remain in place and are situated above the bay floor with the bottom of the wickets at approximately ft. Consequently, the bay entry sill elevation controls the lowest elevation for flow to both turbine bays. Flow into the powerhouse can be controlled by stop logs across the front of the bays. The lowest level achievable will depend on the physical control elevations and the actual hydraulic capacity of the discharge structures (Figures 2-1, A-2, A-3 and A-4). Estimated discharge rating curves for maximum discharge (all stop logs removed) and three different assumptions regarding the culverts are provided in Figures A-2, A-3 and A-4. Figure A-2 illustrates the full discharge capacity assuming that no culverts are used. Figure A-4 provides the estimated discharge capacity assuming all five culverts are opened for flow. These curves are based on an assumed 150 cfs discharge capacity through the larger turbine bay. Figures A-6 and A-7 illustrate the relationship between discharge and reservoir parameters such as surface area, storage, and retention time for discharge without use and with use of the culverts. If it is determined that the culvert lift gates can be removed within project funding constraints and useable for discharge during the initial drawdown period, an assessment will be made considering all factors, including sediment transport, regarding use of one or more of the culverts. The culverts each could have a capacity of approximately 35 cfs with a headwater equal to the crown of the culvert. Based on that estimate, opening three culverts for flow could lower the upstream water level during average summer flow conditions to approximately 604 ft. Opening all five culverts would lower the pond level to approximately ft with a total discharge of 150 cfs. The discharge rating calculations were done within a spreadsheet. Control is based on the lower discharge estimate from basic weir and orifice equations using a single assumed value for the orifice coefficient and weir coefficient throughout the head range. In the spreadsheet, gate openings and discharge coefficients are assigned to each spillway component individually to enable calculating the total discharge for any combination of gate/stop log settings and spillways. The Tainter gate sill is at a relatively high elevation compared to initial drawdown water levels, and the Tainter gate opening is of little consequence. Flow control for initial drawdown range is primarily established by stop log control elevations or the culvert lift gates if used. The discharge rating also includes flow through the two turbine bays in the powerhouse. Discharge through the Unit 1 turbine bay is based on a 6-ft diameter opening in the bay floor since the turbine 8

14 wicket gates and runner have been removed. Flow through the Unit 2 turbine bay is less certain; the wicket gates and runner remain in place and flow is controlled by the opening and elevation of the wicket gates. The bottom elevation of the wicket gates is approximately ft, just below the sill elevation at the inflow to the bays. It was assumed that approximately 150 cfs could pass through the Unit 2 turbine bay when not controlled by the turbine bay entry sill elevation. This is believed to be a conservative estimate since the discharge through the turbine at its rated generation capacity is approximately 400 cfs. The calculated flow capacity of the turbine wicket gates treated as a circular weir/orifice is considerably greater than 400 cfs Existing Streamflow Characteristics Existing streamflow characteristics are an important input to the development of a drawdown plan as drawdown rate and duration is not only influenced by control structure rating capacities, but also contributing streamflow to the pond. The flows in the Boardman River at Sabin Dam are unusually steady. Baseflow as calculated by standard methods is greater than 90% of the total average annual discharge. The 100-year return period peak discharge is estimated to be only two times the 2-year flood discharge. Appendix B provides information related to Boardman River streamflows, including: mean daily flow duration statistics for each month of the year, and high flow frequency data. Extensive analyses of streamflow data from two U.S. Geological Survey (USGS) long-term stations was completed to characterize historical streamflow statistics including mean daily flow duration for each month and peak discharge information annually and by month (Figure B-1). The period of record for the station downstream of Brown Bridge Dam is from 1954 to That station location primarily measures discharge from Brown Bridge Dam, but East Creek also enters the Boardman River just upstream of the station. The statistics indicate a marked difference in runoff characteristics at this station from those at the active station that is upstream of Brown Bridge Pond (Figure B-5). It appears that the East Creek watershed that flows into the Boardman River below Brown Bridge Dam has a more rapid response to precipitation events than does the upper Boardman River watershed. The rates of rise and fall for runoff events are more rapid for the lower station than for the upper station. The runoff volume per unit watershed area is slightly higher for the downstream station, which is assumed to reflect the inflow from East Creek. 9

15 2.2.3 Hydrologic Effects of Initial Drawdown Perhaps the most obvious potential effects are those associated with hydrology. Reasonable concerns include: alteration of Boardman River flows downstream of Sabin Pond resulting from the loss of storage in the reservoir, changes natural resources due to hydrologic alteration, risk of potential damage to infrastructure, and alteration in groundwater levels due to changes in pond water levels. It is not the intent to identify and assess every potential effect; however, potentially significant concerns and effects are addressed. Downstream River Discharge The lowering of the Sabin Pond water level through changed discharge structure operations alters the temporary storage volume and release rates from the structure for a runoff event. The effects of this initial drawdown are distinguished from effects of the dam removal with return to an open river system. Only the effects of the initial drawdown are addressed here. Streamflow effects of the final drawdown phase and dam removal will be addressed in subsequent project studies and plans. The storage volume and vertical fluctuation range in Sabin Pond are small compared to the river inflow rates and volumes. The resulting modification (reduction) in flow provided by Sabin Pond and discharge structures is small. An analysis of the effects of Brown Bridge Pond on river flows indicated a reduction in peak flow in the range of up to approximately 3% at the outlet from the Brown Bridge structure. Routing the same historic discharge hydrographs through the Sabin structure as were used for the Brown Bridge structure indicates smaller impacts on peak discharge rates; the reductions are generally approximately 1%. Reservoir Area The water level in Sabin Pond will be lowered through changing the settings of existing discharge structures. As previously stated, the reservoir level will continue to rise and fall with the conveyance of runoff from precipitation and snow melt events. The hydrologic effects in the reservoir area of interest include: Surface Water: The shoreline zone subject to wave erosion is reduced in elevation and diminished in length (perimeter). The lowered water level results in altered surface runoff erosion potential in the zone between historic pool elevation to the lowered pool elevation. 10

16 Groundwater: Alteration in hydrology for wetlands that have developed as a result of the Sabin Dam construction. Changes in water levels in any water supply wells within the area potentially affected. Changes in soil moisture, potential soil strength changes, and changes in slope stability characteristics. The effects of a lowered groundwater table are difficult to quantify, in general, due to limited data on the stratigraphy and aquifer characteristics around the Sabin Pond. However, because there is limited infrastructure on the Sabin Pond shoreline and because the initial drawdown is limited to approximately 8.5 ft, potential infrastructure effects are assumed to be limited. There are no known structures of significance around the Sabin shoreline that would be of concern with regard to erosion by either wave action or surface flow. Effects to wetlands have been evaluated during the Boardman River Feasibility Study (ECT, 2008). It is expected, however, that new wetlands will become established in the historic restored floodplain and shoreline zone as a part of bottomland restoration. When Sabin Dam is removed and a riverine reach is restored, groundwater levels will return to approximately the historic condition prior to dam construction. The topography of the surrounding slopes and valley has generally not been changed by the construction and existence of the structure. However, there has been some sedimentation in the valley bottom (ponded area) and some shoreline erosion along the pond perimeter (water level fluctuation zone). Rapid drawdown (not proposed here) can have a destabilizing effect on these adjacent slopes. As a result, there does not appear to be significant detrimental effects of water table lowering that are not recognized and acceptable as an effect of restoring the river. Sabin Structures and Dam Embankment The water levels in Sabin Pond and discharges through the outlet structures will be within the ranges of operation of these structures. It is, therefore, assumed that initial lowering will not adversely affect the structure itself. While discharges will be routed through different facilities, the total discharge during drawdown will not differ from flow rates normally observed in the Boardman River as it flows through the Sabin valley. Visual inspections of the flow control structures in support of the initial drawdown will be conducted (1) prior to initiation of the initial drawdown, (2) during the drawdown, and (3) regularly during the subsequent hold-down period until final drawdown. The potential effect on the embankment is related to rapid drawdown resulting in slope failure and shoreline erosion caused by easterly long-shore wave action, though westerly winds prevail in this region. 11

17 The drawdown rate will be made at a safe, controlled rate to avoid rapid drawdown conditions that might cause slope instability at the embankment or along the reservoir rim. Regular inspections as described above will look for embankment erosion at the new and former shorelines. The embankment is expected to be subject to this condition for a period of approximately one year or less and erosion controls can be implemented if needed Sediment Transport and Water Quality Effects The initial drawdown will lower the Sabin Pond water level by approximately 8.5 ft or less (current water level of approximate elevation 611 ft to the lowest expected level of approximate elevation ft). The lowest level hydraulically achievable will depend on the actual hydraulic capacity of the flow control structures (Section 2.2.2). Lowering the water level to ft would expose virtually the entire Sabin Pond bottom, or 38 acres of previously inundated bottomlands. It will also change the hydraulic conditions and sediment transport capacity of the Boardman River channel, causing erosion of the channel as it adjusts to the new hydraulic conditions. Similar erosion of stream channels will occur at any other small tributaries into the reservoir that have deposited deltas during the life of the reservoir. An assessment of the erosion, sediment transport, settling characteristics, and observations from a recently conducted on-site geomorphological assessment for the Boardman River delta area and Sabin Pond is more fully discussed in Section 3.0 of this report Fishery Effects Fish communities that would potentially be affected by the drawdown of Sabin Pond include those within the pond itself and those immediately downstream of the dam. The minimum pond level that can be achieved using only the existing discharge facilities will provide a reduction in the surface area of the pond to approximately six acres, leaving previously inundated near shore areas dry. A drawdown occurring in the spring or early summer could affect generally warm water lentic species that utilize these shallow, often vegetated, littoral areas as spawning and nursery habitat. The reduced water volume in the pond could also affect the resident community, which presumably consists of a mixture of warm-cool water lentic and lotic species. The warm-cool water lentic species will likely be affected by the reduced habitat size, but the decision to carry out this project implies that the overall ecologic value gained from the anticipated system restoration outweighs the impact on these species that are found in abundance in naturally lotic systems found elsewhere in the watershed. 12

18 The fish community in the Boardman River downstream of the Sabin Dam could potentially be stressed by the drawdown if the incoming water was extremely turbid (suspended solids heavily dominated by fines <0.62 millimeters [mm] comprised of organics and clay), or if substantial amounts of entrained sediments (0.062 to 2 mm) were released. The pond upstream of Sabin Dam will become progressively smaller as the drawdown elevation is lowered, being effectively eliminated at the lowest levels possible. But assuming monitoring of sediment concentration and/or turbidity is effective at identifying excessive conditions, resulting in termination of the drawdown or even triggering raising of the controlled water level, the downstream fish community should not be adversely affected. It is not expected that there will be significant impacts to fish, it any, if they pass through the spillway, culverts, etc. during drawdown. Other sediment management practices will be implemented as needed around the pond perimeter to control those potential sediment sources. These controls are expected to provide discharges that will not cause significant adverse effects for fish in the river downstream of Sabin Dam; particularly if drawdown timing occurs outside of sensitive life stages of the dominant fish community. From a seasonal perspective, the least effect on fisheries from the initial drawdown would be to perform it in mid-summer to early autumn. In the spring and summer, many species use the shallow, littoral areas as spawning and/or nursery habitat. A drawdown during this period would likely increase mortality and inhibit recruitment success for that year s cohort for warm-cool water lentic species. However, as stated above, such a loss in recruitment is not considered to be a significant issue, given the overall objectives of restoring the existing lentic system to a lotic environment. 2.3 SUMMARY OF ANALYSES AND FINDINGS FOR PLAN FORMULATION The capability to drawdown the Sabin Pond over a short time interval at any time of the year, even the very regular high flow period of April, exists. If the culverts within the auxiliary spillway are used (the wooden lift gates can be removed), the water level in the pond can be lowered significantly more than without use of the culverts. In that condition sediment scouring within the impoundment and control of sediment discharge to the downstream channel will be a bigger challenge. The drawdown plan as described in Section 2.4, is primarily one of (1) selecting the timing for the drawdown to avoid or minimize any seasonally related adverse effects and take advantage of any seasonally related benefits, and (2) establishing the desired rate(s) of water level lowering to avoid or minimize adverse effects of a particular rate of water level lowering. The actual minimum water level in Sabin is expected to be determined by acceptable sediment discharge rates observed through monitoring. 13

19 2.3.1 Seasonal Considerations The seasonal variation in streamflow is summarized in flow duration data provided in Appendix B, Figures B-4 and B-5 and Table B-1. The mid- to late-summer drawdown offers the advantage of lowest streamflows, least risk of large runoff event, lowest wind speeds affecting wind generated wave turbidity, establishment of vegetation in newly exposed areas for erosion control, and fastest drying and consolidation of newly exposed sediments. From a seasonal perspective, therefore, the drawdown should ideally begin in late June or early July Drawdown Rates The storage volume in Sabin Pond is relatively small relative to streamflow rates, and the initial drawdown of up to approximately 8.5 ft could be accomplished based on only hydraulic controls easily and quickly, barring high flow events. The rate of drawdown is primarily established by considerations of sediment transport and fish stranding. Sediment transport concerns become more significant at lower drawdown water levels as a significant percentage of the entire Sabin Pond bottom becomes exposed and the remaining pond size to control sediment discharge becomes smaller and ineffective as a control on sediment release. Based on these identified factors, a relatively slow drawdown rate can be implemented without risk of reducing or impacting any of the project goals. A drawdown rate of a maximum of 0.5 ft per day with an average rate not exceeding 0.3 ft per day appears a reasonable target. Because flow control will be primarily by stop log removal, flow control is somewhat limited to practical increments of stop log size (i.e., length and in-place vertical dimension). The stop logs controlling flow into the Unit 1 turbine bay are 16 ft long and have a vertical dimension of approximately 0.5 ft. The stop logs controlling flow into the Unit 2 turbine bay are 25 ft long and have a vertical dimension of approximately 0.5 ft. At an inflow rate of 150 cfs, for example, removal of one stop log from the old turbine bay would drop the water level 0.5 ft in approximately three hours. 2.4 DISCHARGE AND WATER LEVEL CONTROL PLAN Schedule Based on the seasonal flow patterns described in Section 2.3, the recommended period of initial drawdown is during the months of July and August (Figure 2-2). The initial drawdown is recommended as beginning in the end of July, assuming that unusually high flow conditions do not exist on that date and the appropriate permits are received. Should high flows exist on that date; the drawdown will be initiated 14

20 when the flow at USGS Station falls below 250 cfs. During the initial drawdown, the Sabin Pond water level will be lowered at an average rate of approximately 0.3 ft per day with a maximum rate of 0.5 ft per day. Because the only flow controls within the range of the initial drawdown water levels are stop logs, the discharge adjustments to be made during a high flow event include installing stop logs and perhaps closing wicket gates on the Unit 2 turbine. Flow records indicate a low risk of having a significant increase in flow during July and August. With a fixed discharge control, a pond level increase due to a high flow event may result in pond water levels falling back to pre-event levels at rates faster than 0.5 ft per day. Stranding of fish in isolated depressions following a temporary rise may potentially occur and would need to be monitored and actions taken as appropriate. The pond water levels and control may be adjusted to avoid use of flow through the Unit 2 turbine bay if excessive debris accumulation becomes a problem Drawdown Implementation Logistics Implementing the Sabin Pond initial drawdown is a relatively simple task. Barring occurrence of a high flow event, it is a matter of removing stop logs to draw down the pond level at the target average rate while not exceeding the maximum drawdown rate Project Requirements and Criteria Regulatory Requirements An MDEQ Joint Permit Application (JPA) permit pursuant to Part 315 of the Natural Resources and Environmental Protection Act (NREPA) is required to support the initial drawdown of Sabin Pond. The County submitted the JPA to the MDEQ on May 23, Project Criteria In addition to the regulatory requirements, project criteria for this CIDP include needs for monitoring of structures and guidance for responding to the range of potential hydrologic conditions. Provided that the equipment functions as intended, nearly any runoff event with a reasonable risk of occurring during the one-year period of the initial drawdown can be passed through Sabin Dam without increased risk. Comparing the estimated discharge capacity (Figure 2-5) with the flood discharge - frequency data 15

21 (Figure 2-4), the Sabin spillway capacity appears to be sufficient to pass even large flood event peak flows. 16

22 3.0 SEDIMENT MANAGEMENT PLAN 3.1 INITIAL DRAWDOWN POTENTIAL EFFECTS The impoundment behind Sabin Dam is small and immediately downstream of Boardman Dam (Figure 3-1). The impoundment is narrow and elongated, flowing south to north. Although most of the coarsegrained sediment was likely trapped in the impoundment behind Boardman Dam historically, fine-grained sediments were transported through and were deposited in the Sabin impoundment. Because of its small size, the fine sand and silt deposited throughout the Sabin impoundment rather than in the form of a delta as is common in larger natural lakes or impoundments. The lowering of the water surface elevation during the proposed drawdown will impact these deposited sediments within the impoundment and this will have impacts downstream of Sabin Dam. The maximum rate of drawdown, as proposed in the initial drawdown plan, is 0.5 ft per day with a maximum average rate not exceeding 0.3 ft per day. Assuming the drawdown will begin with the current water elevation of 611 ft, it will take approximately 14 days to draw down the impoundment to the lowest expected level without use of the culverts (elevation 607 ft). Portions of the impounded sediment in the Sabin impoundment are already exposed. Because much of the impoundment has experienced sediment deposition, a much greater percentage of the impoundment will become exposed with a 4-ft drawdown to 607 ft than in the Brown Bridge impoundment following a 3-ft drawdown in The Sabin impoundment will only extend about 800 ft upstream of the dam following drawdown to 607 ft (Figure 3-1). With this drawdown level, there are likely to be impacts to the channel within the impoundment as well as to the Boardman River downstream of the dam. As discussed in detail below, the primary impact within the impoundment will be the formation of a channel through the exposed impounded sediments. Impacts to the Boardman River downstream of the dam will result from the downstream transport of the sediment eroded in the impoundment during the formation of a new channel. Minor changes are discussed below as well Impoundment Sediments Drawdown of the Sabin impoundment to an elevation of approximately 607 ft will expose about 32 acres of previously inundated reservoir bottom (about four acres are already exposed). As the impoundment decreases in size, the Boardman River will begin to form a new channel by moving sediment downstream. The Sabin impoundment is relatively narrow and the location of the historic floodplains is still detectable because of exposed tree stumps. The deepest parts of the impoundment are between concentrated areas of stumps, likely the location of the historic Boardman River channel. During the drawdown, the Boardman 17

23 River will likely form in these deep areas of the impoundment and in the channel s historic location. The one area where this may not occur is at the upstream end of the impoundment where the outlet of Boardman Dam directs water flow over a historic floodplain before it meets the former channel location (Photo 3-1). Existing Channel Flow Stumps from Historic Floodplain Possible Historic Channel Photo 3-1: Upper extent of the Sabin impoundment looking upstream, at existing channel emanating from the Boardman Dam spillway (left side of picture) and likely historic channel (right side of picture). Drawdown will result in the Boardman River cutting through impounded sediments to reach a more stable gradient. The knickpoint created by this drawdown will migrate upstream through the impounded sediments, but will likely stop where the former channel location meets the former floodplain location. At a water level of 611 ft, most of the upper end of the reservoir bottomland is exposed. With a drawdown to 607 ft, these areas will experience two to four ft of channel incision (Figure 3-2). As the channel incises through the impounded sediment, the side slopes will also likely erode until they attain a stable angle. This eroded impounded sediment will move downstream during and after the drawdown. Continued drawdown by use of the culverts will extend the channel incision process, lowering the channel thalweg while reducing the remaining pool size. 18

24 Some amount of the eroded material will likely be deposited in the deeper portions of the remaining impoundment near the dam, but the trapping capacity of the impoundment will be much diminished. Under low flows (approximately 100 cfs), the residence time of water in the remaining impoundment will be approximately two hours. However, flows are rarely as low as 100 cfs at Sabin. Under higher flows, this residence time will decrease substantially. Figures A-6 and A-7 provide a graphical relationship between river flow rate and retention time for two outlet control settings. With such a short residence time, it is likely that fine-grained material will remain in suspension and move downstream of the Sabin Dam with the discharged water. The volume of this sediment moving downstream is unknown. Even though the channel slope downstream of Sabin Dam is much lower than the historic channel upstream, the sediment mobilized downstream will likely consist primarily of finer-grained sands and silts, and this material may continue to stay in suspension until reaching Boardman Lake. Fine-grained sediment, moving downstream of Sabin Dam, present two potential problems. First, accumulations of sediment in the form of a delta or otherwise in Boardman Lake may not be desired. Boardman Lake is a large lake with substantial recreational opportunities and this sediment may negatively impact this recreation. Second, turbidity of the water may increase with decreased clarity, but contaminants associated with sediment in Sabin Pond are not considered problematic based on sampling conducted in 2005 and 2010 (Appendix D) Steep Hill Slopes The Sabin impoundment is bounded by steep slopes, particularly in the areas close to the dam. Some concern has been expressed that these slopes will become destabilized once the drawdown occurs because the toe of the slope will no longer be protected. Although some erosion may occur, the field investigation resulted in observations of very steep slopes that were stable and showed no signs of instability even though the impoundment was drawn down a few ft exposing un-vegetated surfaces near the toe (Photo 3-2). The existing vegetated slopes are likely much steeper than the slopes that will become exposed. The exposed surfaces will likely become vegetated, thus reducing erosion. Based on field observations, it is unlikely that large portions of hill slope will fail following drawdown. 19

25 Steep toe slope Exposed, unvegetated surface following drawdown Photo 3-2: Stable steep toe slope despite exposed ground below Adjacent Tributaries Although no tributaries are identified on the USGS topographic maps, a few tributaries in the upper half of the impoundment were identified on the plat maps from the mid-1800s (Figure 3-3). Although none of these tributaries were observed during the field investigation, many seeps were found along the edge of the impoundment, particularly the west slope. These seeps have deposited small deltas of fine sand and silt (Photo 3-3). As the drawdown occurs, the water from these seeps will erode through these small deltas. The impact of this erosion will likely be minimal. As was observed in the Brown Bridge impoundment in 2008, the seeps will erode through the sediment until it reaches the hill slope and its original grade, at which point the erosion/incision will likely halt. 20

26 Fine Sand Delta Photo 3-3: Seep water from the valley wall incising through the delta it formed (left) that can be as much as 4.5 ft in depth (right). 3.2 SEDIMENT MANAGEMENT RECOMMENDATIONS DURING INITIAL DRAWDOWN A few concerns exist regarding the drawdown of the Sabin impoundment. Although the historic channel alignment was tentatively identified in a few locations and could probably be confirmed with a more detailed investigation, sediment has been deposited throughout the impoundment and an exposed intact channel is not likely to exist. As the impoundment shrinks during the drawdown, the Boardman River will mobilize sediments as it forms a new channel. With limited trapping capacity and short residence times, much of the finer-grained sediment will likely remain in suspension and be mobilized downstream of the dam. Some of these sediments may deposit in the slack-water areas of the Boardman River downstream of the dam while much of the sediment will likely be carried through to the Union Street impoundment, depending on the flow regime. Based on previous work with other dam removal projects, contaminant levels that exceed the Probable Effects Criteria (PEC) are typically the trigger for active management of contaminated sediment. Constituents of concern for the sediment impounded behind Sabin Dam are low and none exceed either the PEC thresholds or the Threshold Effects Criteria (TEC) (Appendix D). 21

27 Downstream transport of fine-grained sediment will likely occur at a Sabin Pond level higher than can be achieved by manipulation of existing outlet controls at Sabin, but the volume and effects of this are unknown. To minimize the downstream transport of fine-grained sediment, we recommend a slow drawdown and frequent monitoring. A drawdown of 0.3 ft per day will allow more time for the sediments to dry and begin to stabilize. It will also provide more time for monitoring. Monitoring should focus on the amount of channel incision and erosion occurring in the impoundment and the movement of the material downstream of Sabin Dam. If sediment does appear to be moving downstream of the dam, the drawdown may be halted and stop logs could actually be replaced to raise the pond elevation and eliminate the downstream transport of sediments. Inundated areas at various Sabin water levels are illustrated on Figure

28 4.0 RE-VEGETATION PLAN Dam removal will create opportunities for invasive species to become established. In particular, dam removal will create large expanses of previously inundated and un-vegetated soils that may be colonized by invasive plant species which may out-compete desirable native plant species. Furthermore, the change in aquatic habitat type from reservoir to free-flowing river may also provide opportunities for aquatic invasive species to become established or spread. An ISMP identifies and prioritizes species to be controlled and provides the methods and procedures for control of invasive species during dam removal and subsequent river/floodplain restoration. As much as 27 acres (excluding approximately five acres for the remaining channel) of previously inundated bottomlands could be exposed with the maximum drawdown of Sabin Pond. Newly exposed soils will re-vegetate through natural recruitment and germination of the existing seed bank. These areas will be actively monitored in accordance with the ISMP. If erosion or invasive species become problematic, erosion control measures will be implemented along with targeted herbicide treatment and/or areas planted as deemed necessary. 23

29 5.0 MONITORING AND REPORTING Monitoring to be performed during the initial drawdown and hold-down period falls into various types, including monitoring of flows and water levels, water quality, erosion, wildlife and monitoring of equipment and structures. In addition, fish rescue, record keeping, reporting, photo documentation, and public notifications are discussed below. 5.1 STREAMFLOW AND RESERVOIR LEVEL During the initial drawdown phase, gate settings will need to be adjusted to accomplish the water level lowering at rates not exceeding the maximum rate. Discharge rate versus pool elevation relationships have been developed for all the gated discharge structures. While uncertainties in these discharge ratings exist, they provide a guide to estimate gate openings needed based on the inflow to Sabin Pond. Inflow rates will be available from the USGS real-time station located approximately one mile upstream of the pond: Station Boardman River above Brown Bridge Road near Mayfield ( After the initial minimum drawdown elevation has been achieved and held for at least one week, the discharge gate settings are not expected to require further changes except for specific needs that may arise; it is not anticipated that discharge gate settings will be changed in response to runoff events. Pond levels will be monitored and levels recorded not less than once per day. The water level, gate and stop log settings, and other information will be recorded as described in Section EROSION, SEDIMENTATION AND WATER QUALITY An inspection of reservoir erosion, sedimentation conditions and field water quality will be made as described in the following sections. 5.3 MONITORING SEDIMENT MIGRATION Since the process of drawdown is reversible, the potential transport of sediment can be managed during the drawdown process. Turbidity downstream is expected but should be greatest following a change in pond elevation, then decrease with time. If turbidity is sustained downstream at high levels, increasing water level may be warranted. Turbidity instruments can provide more quantitative measures to augment visual assessments if desired. The greatest risk for sediment transport is associated with floods. Regardless of their magnitude or duration, floods during the drawdown period will move the greatest 24

30 volume of fine material downstream and out of the impoundment. If significant rainfall is anticipated, raising the pond level to reduce the transport of sediment may be warranted. The patterns of sediment deposition below the dam should be monitored to ensure the volume and rate of deposition is manageable. Localized patterns of deposition are acceptable, as fish and other mobile species can occupy clean areas within the river; however, dispersed and ubiquitous deposition of fine sediment presents a management challenge and should be avoided. If these patterns of deposition appear, further dewatering without active sediment management measures should be avoided. 5.4 MONITORING TRIBUTARY CHANGES As the drawdown progresses, if old unnamed tributaries do not stabilize at their original base levels and proceed to cut deeper into their channels, steps may be taken to mitigate the rate of change. In particular, the addition of logs, found or cut on site, into the channels at strategic locations can help provide grade control, limiting the gullying effect. These measures can be accomplished by hand and will provide temporary control of incision until more permanent efforts, if deemed necessary, can be examined. Emphasis should be placed on controlling the rate of change, not forcing the streams to stop adjusting. Tenuous action to halt adjustment is contrary to the overall momentum and trajectory toward restoration of the pattern, profile and dimensions of the stable condition and thus will have questionable, long term, persistence in the channel; or in the worse case, could potentially contribute to channel degradation/aggradation and a corresponding increase in time to reach channel stability. 5.5 MONITORING STEEP HILL SLOPES Monitoring the situation on the hill slopes near the dam should focus on revealed areas on the lower slope during drawdown. Areas of failure associated with large slumps or calving into the impoundment are serious signs of instability and should illicit immediate action. During the growing season, the development of vegetation will add further protection to exposed surfaces. 5.6 FISH RESCUE The applicant (under the guidance and supervision of the Michigan Department of Natural Resources [MDNR] Fisheries Division and Grand Traverse Band of Ottawa and Chippewa Indians) will monitor the drawdown for fish stranding and rescue. Appropriate fish transfers will occur through all applicable permits, guidance, and supervision of the MDNR Fisheries Division and Grand Traverse Band of Ottawa and Chippewa Indians. A report documenting this activity will be prepared and made available to the MDEQ within ten days of the conclusion of the drawdown for review and inclusion into the subject file. The applicant will not transfer any fish species from isolated pools (resulting from the drawdown) to the 25

31 Boardman River that will negatively affect the fish community of the Boardman River, such as exotic or invasive species such as the round goby. 5.7 SABIN STRUCTURE An inspection of the discharge gates, discharge apron and banks, trash racks, log boom, and earthen embankment will be made not less than once each day during the initial lowering phase. Inspections will be made at least twice a week by Grand Traverse County (County) during the hold-down phase. The inspection will be documented on a standard inspection form. 5.8 RECORD-KEEPING Records of conditions existing during the drawdown and inspection observations will be maintained. Inspection observations related to the facility structures, including the discharge gates, turbines, dam, and spillway will be maintained on the inspection form presented in Appendix C. Inspections related to sediment management are addressed in Section PROJECT REPORTING A brief status report will be submitted to the Implementation Team once each week during the initial drawdown phase and monthly during the hold-down phase DRAWDOWN PLAN MODIFICATIONS This drawdown plan is a dynamic document and will be modified as appropriate based on different conditions. The condition of the wooden lift gates at the culverts will be determined during the drawdown and, along with the observations regarding channel incision and sediment discharge, dictate cessation of further drawdown EMERGENCY PREPAREDNESS The existing Sabin Dam Emergency Action Plan (Grand Traverse County, 2009) provides information appropriate for use should any emergency conditions develop during the drawdown and hold-down period PHOTO DOCUMENTATION At least three photo documentation stations will be established at key vantage points adjacent to Sabin Pond and the Boardman River in the drawdown area of concern. Station stakes or markers will be fixed in place with arrows indicating the direction the photo will be taken. At least three photos at each location will be taken from the same vantage point as indicated by the station marker and arrows, using 26

32 the camera s wide angle setting. Each photo will be overlapped to some extent to allow creation of a panoramic encompassing scene. Photos will be time and date stamped and photo file identifications recorded in a log book. Photos at the stations will be recorded on a daily basis starting the day prior to initiating the drawdown. Select series of photos will be reviewed and posted weekly on one of the Boardman River Websites for public access PUBLIC NOTIFICATIONS AND COMMUNICATIONS It is important to make information regarding the drawdown available to the interested public and stakeholders. This will occur through regular project reporting to the County. Press releases and pertinent information will be posted on the Boardman River Website ( In addition, the County will create and place as appropriate, signage along areas around Sabin Pond and the adjacent Boardman River that have steep slopes, erosion, soft bottom, etc (e.g., the potential to be unsafe). 27

33 6.0 REFERENCES Cummings, T.R., J.L. Gillespie and N.C. Grannemann, Hydrology and Land Use in Grand Traverse County, MI. USGS Water-Resources Investigations Report Environmental Consulting & Technology, Inc., Boardman River Feasibility Study, Detailed Analysis of Alternatives Report. Grand Traverse County, Emergency Action Plan, Sabin Dam, National Inventory of Dams No. MI Harza Engineering Co., Boardman River No. 2 Project, Michigan Public Service Company. Engineering Drawings (29 sheets). URS, HEC-RAS Hydraulic Model for Boardman River, May Prepared for U.S. Army Engineers, Detroit District. U.S. Geological Survey. National Water Information System: Web Interface. Station Boardman River above Brown Bridge Road near Mayfield, MI and Station Boardman River near Mayfield, MI. 28

34 FIGURES Sabin Pond Comprehensive Initial Drawdown Plan

35

36

37 Figure 2-1. Sabin Outlet Facilities Sabin Pond Comprehensive Initial Drawdown Plan

38 Figure 2-2. Boardman River Flow Duration Data at Sabin (MDEQ) Sabin Pond Comprehensive Initial Drawdown Plan

39 Figure 2-3. Boardman River Flow Duration Data at Sabin (MDEQ Compared to USGS Station )

40 Figure 2-4. Flood Discharge Frequency Data for Boardman River at Sabin Dam Based on MDEQ Flood Discharge Database

41 Figure 2-5. Sabin Discharge Capacity - Powerhouse and Spillway Discharges (No Culvert Discharge)

42 Figure 2-6. Sabin Discharge Capacity - Powerhouse and Spillway Discharges (All Five Culverts Open)

43

44

45

46 APPENDIX A SABIN STRUCTURE HYDRAULIC INFORMATION Table A-1 Sabin Dam Discharge Facility Data Figure A-1 Sabin Dam and Spillway Plan View Figure A-2 Sabin Discharge Capacity Powerhouse and Spillway Discharges (No Culverts Open) Figure A-3 Sabin Discharge Capacity Powerhouse and Spillway Discharges (Two Culverts Open) Figure A-4 Sabin Discharge Capacity Powerhouse and Spillway Discharges (All Five Culverts Open) Figure A-5 Sabin Pond Elevation Area and Elevation Storage Curves Table A-2 Sabin Pond Elevation Area and Storage Data Figure A-6 Sabin Pond, Discharge versus Surface Area, Storage Volume, and Retention Time (Culverts Not Used) Figure A-7 Sabin Pond, Discharge versus Surface Area, Storage Volume, and Retention Time (All Culverts Used) Figure A-8 Sabin Bathymetric Map/Aerial Image (2010)

47 Sabin Structure Hydraulic Information Appendix A provides a summary of basic hydraulic information for the Sabin discharge facilities and the impoundment relevant to development of the Initial Drawdown Plan. This information includes: Summary of discharge facilities data Estimated discharge rating relationships for the discharge facilities Sabin Pond elevation area storage relationships Sabin Pond bathymetric map Sabin Pond relationship between steady flow rate, surface area, storage volume, and retention time

48 Discharge Rating Relationships Discharge rating relationships were developed based on basic weir and orifice flow equations for the Tainter gate, auxiliary spillway overflow, and flow through the two powerhouse turbine bays. Characteristics of the structures at the dam are summarized in Table A-1. The calculations were done within a spreadsheet. Control is based on the lower discharge estimate from basic weir and orifice equations using a single assumed value for the orifice coefficient and weir coefficient throughout the head range. In the spreadsheet, gate openings and discharge coefficients are assigned to each spillway/discharge component individually to enable calculating the total discharge for any combination of discharge arrangement/settings. The discharge rating also includes flow through the two powerhouse turbine bays. All equipment has been removed from the older, smaller, turbine bay leaving an approximately 6-ft diameter opening in the bay floor (Harza, 1930, drawing no. 2BR-13). The bay floor is at a lower level than the sill controlling flow into the bay (see Figure 2-1. Sabin Outlet Facilities). The newer, larger, turbine bay still has the turbine wicket gates and runner in place. The elevation of the bottom of the wicket gates is at approximately ft based on construction drawings, or slightly below the sill elevation at the entry into the turbine bay. It was assumed that the flow capacity through the newer turbine bay is 150 cubic feet per second (cfs); the unit rated flow is estimated to be approximately 400 cfs based on the rated capacity and head. Flow to the newer turbine bay may be less for lower water levels if controlled by weir flow over the sill entry into the turbine bay. Flow through the older turbine bay is estimated from the controlling (lesser) flow, either weir flow over the bay entry sill or orifice flow through the horizontal turbine opening in the floor. The five culverts incorporated into the auxiliary spillway structure have wooden lift gates that control flow into the culverts. The condition of these gates is not known. If the lift gates are removed, the water level in Sabin Pond could be lowered an additional four to five ft below the lowest level using only the turbine bays. However, the Sabin Pond storage volume, which provides settling/capture of suspended sediment if flow is slowed sufficiently and the retention time sufficient, is very much reduced For Sabin Pond, high flow events are large enough and rates of change and duration long enough that storage in the pond has little influence on the flow through the pond and resulting water level; that is, the water level will be controlled by the discharge capacity of the outlet works and not be significantly influenced by storage changes. Assuming a direct relationship between discharge capacity and Sabin Pond water level, a direct relationship between flow rate (river inflow and discharge from Sabin Pond) and the pond surface area, storage volume, and retention time also exists. Graphs of these parameters for two discharge rating relationships, one assuming maximum discharge capacity without use of the culverts and the other maximum discharge capacity including use of the five culverts, are provided in Figures A-6 and A-7, respectively. The retention time in Sabin Pond is not large for either condition. Without opening the culverts, and recognizing the flow in Boardman River at Sabin is estimated to rarely be less than 100 cfs, Figure A-6 indicates a retention time in the range of 0.7 to 1.3 hours for the entire flow range of anticipated potential river flows. If the lift gates are removed and the culverts used for discharge, the retention time is only approximately 0.1 hour for flows less than approximately 400 cfs and increases to approximately 0.25 hour for flows from 500 cfs to 1000 cfs. These are maximum retention times assuming that the entire Sabin Pond volume would be effective storage. Some inefficiencies resulting from ineffective flow areas in the pond can be expected, reducing these estimated retention times by some amount.

49 Table A-1. Sabin Dam Discharge Facility Data Facility Attribute/Element Tainter Gate Auxiliary Spillway Powerhouse Discharge Characteristics 1 to 18 ft wide by 5.5 ft high Tainter Gate with sill elevation ft 32 ft wide overflow with crest elevation approximately ft; stop logs to ft used to raise overflow elevation 5 culverts; (approximately elliptical shape with 60-inch span by 27-inch rise); upstream invert at approximate elevation ft; wooden lift gates control discharge; condition of lift gates unknown Old Turbine Bay (wicket gates removed; approximately 6 ft diameter circular opening in floor at elevation ft [approximate]; sill entry into bay approximately 16 ft wide at approximate elevation ft). Flow to the turbine bay can be controlled by timber stop logs with approximately 6-inch by 8-inch section dimensions. New Turbine Bay (wicket gates still in place; wicket gates approximately 2 ft above bay floor; estimated zero discharge elevation at approximately 606 ft; 500 kilowatts [kw]/800 horsepower [HP] rating)

50 (source: Grand Traverse County, January 2009) Figure A-1. Sabin Dam and Spillway Plan View

51 Figure A-2. Sabin Discharge Capacity - Powerhouse and Spillway Discharges (No Culverts Open)

52 Figure A-3. Sabin Discharge Capacity - Powerhouse and Spillway Discharges (Two Culverts Open)

53 Figure A-4. Sabin Discharge Capacity - Powerhouse and Spillway Discharges (All Five Culverts Open)

54 Figure A-5. Sabin Pond Elevation Area and Elevation Storage Curves Sabin Pond Comprehensive Initial Drawdown Plan

55 Table A-2. Sabin Pond Elevation Area and Elevation Storage Data Elevation Pool Shoreline Storage Area Area Below Above (ft) (acres) (acres) (ac-ft) (ac-ft)

56 Figure A-6. Sabin Pond, Discharge versus Surface Area, Storage Volume, and Retention Time (Culverts Not Used)

57 Figure A-7. Sabin Pond, Discharge versus Surface Area, Storage Volume, and Retention Time (All Culverts Used)

58 Figure A-8. Sabin Pond Bathymetric Map/Aerial Image (2010) Sabin Pond Comprehensive Initial Drawdown Plan

59 APPENDIX B EXISTING CONDITION STREAMFLOW CHARACTERISTICS Figure B-1 Figure B-2 Figure B-3 Figure B-4 Figure B-5 Table B-1 Table B-2 Figure B-6 Figure B-7 Table B-3 Table B-4 Boardman River Contributing Drainage Area USGS Water Quality Study Synoptic Streamflow Measurements (Linear Regression) USGS Water Quality Study Synoptic Streamflow Measurements (Power Equation Regression) Daily Mean Flow Duration Curves; USGS Station Boardman River above Brown Bridge Road Exceedance Flows (1%, 10%, 50%, and 90%) by Month for USGS Stations above and below Brown Bridge Pond Daily Mean Flow Duration Curves; USGS Station Boardman River above Brown Bridge Road Maximum Mean Daily Discharge Data by Month USGS Annual Peak Discharge Series Plot USGS , Boardman River above Brown Bridge Road near Mayfield USGS Annual Peak Discharge Series Plot USGS , Boardman River near Mayfield Peak Discharge Frequency Estimates; USGS Station Boardman River above Brown Bridge Road Peak Discharge Frequency Estimates; USGS Station Boardman River near Mayfield

60 Existing Condition Streamflow Characteristics Appendix B provides information related to Boardman River streamflows, including: mean daily flow duration statistics for each month of the year, and high flow frequency data. Boardman River streamflow data are available from two USGS long-term streamflow stations. However, both of these stations, one active station located 19 river miles upstream of the dam and one inactive station located 14 river miles upstream from Sabin dam. Due to topography and soils, there are portions of the Boardman River watershed that are considered non-contributing. MDEQ identifies the total drainage area and the contributing drainage area in some of the records in the MDEQ flood discharge database. That information is summarized graphically in Figure B-1. While non-contributing areas will occur in upper portions of tributaries, the data when plotted indicate an approximately linear relationship with the contributing area being approximately 78% of the total topographic watershed. This watershed characteristic is significant when transferring the USGS streamflow station data to downstream locations based on drainage areas. The USGS has made numerous streamflow measurements at other locations in the Boardman watershed for a hydrology and water quality study project (Cummings et al, 1990). Several water quality sampling events were completed over a period from 1984 to 1986 at various locations. Instantaneous flow measurements were made; typically these events appear to have been sampled over a period of two or three days. The only information provided in the USGS web-based database is date of measurement, so the precise time is not readily available nor is more general information regarding rainfall or information describing the phase of the runoff event. It appears that the sampling events included dry weather and runoff events, which is common for water quality sampling programs. Selected flow measurements available from that USGS hydrology study are plotted in Figures B-2 and B- 3 with events identified as synoptic events. Figure B-2 includes fitted linear regression relationships for each event while Figure B-3 is the same data with power equation regression relationships. Since the measurements were collected over a period of two to three days, they are not truly synoptic, and Boardman River flows may have changed significantly over the two or three day periods. With these limitations in mind, the information is still useful as it provides some insight into the variation in streamflow along the river. It is anticipated that the flow conditions may have been relatively steady during the July 31 through August 1, 1984 sampling event and that relationship indicates a slight decrease in flow per unit drainage area. This would be consistent with a high baseflow source in the upper portion of the watershed with the lower portion of the watershed providing baseflow at a lower rate. Extensive analyses of streamflow data from two USGS long-term stations was completed to characterize historical streamflow statistics including mean daily flow duration for each month and peak discharge information annually and by month. The period of record for the Station downstream of Brown Bridge Dam is from 1954 through That station location is primarily discharge from Brown Bridge Dam, but East Creek also enters the Boardman River just upstream of the station. The statistics indicate a marked difference in runoff characteristics at this station from those at the active station that is upstream of Brown Bridge Pond. It appears that the East Creek watershed has a more rapid response to precipitation events than does the upper Boardman River watershed. The rates of rise and fall for runoff events are more rapid for the lower station than for the upper station. The runoff volume per unit watershed area is slightly higher for the downstream station, which is assumed to reflect the inflow from East Creek.

61 The MDEQ provides some flow duration statistics at various locations along the Boardman River in the web-based streamflow data. These data are plotted in Figures 2-3. The MDEQ data for the Sabin Dam location are compared with data from the USGS stations in Figure 2-4. The method used by MDEQ to develop their estimates is not described on the web page.

62 Figure B-1. Boardman River Contributing Drainage Area Sabin Pond Comprehensive Initial Drawdown Plan

63 Figure B-2. USGS Water Quality Study Synoptic Streamflow Measurements (Linear Regression)

64 Figure B-3. USGS Water Quality Study Synoptic Streamflow Measurements (Power Equation Regression)

65 450 Boardman River above Brown Bridge Road (Period of Record Sep 1997 Dec 2010) 400 Mean Daily Discharge (cfs) January February March April May June July August September October November December Fraction of Days Non Exceedance Figure B-4. Daily Mean Flow Duration Curves; USGS Station Boardman River above Brown Bridge Road

66 700 USGS Station Boardman River above Brown Bridge Road ( ) USGS Station Boardman River near Mayfield ( ) (D/S) 600 Mean Daily Discharge (cfs) % (D/S) 10% (D/S) 50% (D/S) 90% (D/S) 10% 50% 90% 1% Month (Jan - Dec) Figure B-5. Exceedance Flows (1%, 10%, 50%, and 90%) by Month for USGS Stations above and below Brown Bridge Pond

67 Table B-1. Daily Mean Flow Duration Curves; USGS Station Boardman River above Brown Bridge Road Fraction Mean Daily Discharge (cfs) Exceed. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Table B-2. Maximum Mean Daily Discharge Data by Month Return Mean Daily Discharge (cfs) 1 Period 2 (years) March April May June July August (USGS Station Boardman River above Brown Bridge Road; September 1997 December 2010) 2 (based on Annual Maximum Series)

68 Figure B-6. USGS Annual Peak Discharge Series Plot USGS , Boardman River above Brown Bridge Road near Mayfield

69 Figure B-7. USGS Annual Peak Discharge Series Plot USGS , Boardman River near Mayfield

70 Table B-3. Peak Discharge Frequency Estimates; USGS Station Boardman River above Brown Bridge Road Annual Exceedance Probability Return Period (Years) 'Expected 95-Pct Confidence Limits for Bull. 17B Estimates Ann. Max Partial Duration Bull. 17B Estimate Systematic Record Probability' Estimate Lower Upper MDNRE Flood Discharge Database Record (at Brown Bridge Road) MDNR a

71 Table B-4. Peak Discharge Frequency Estimates; USGS Station Boardman River near Mayfield Annual Exceedance Probability Return Period (Years) 'Expected 95-Pct Confidence Limits for Bull. 17B Estimates Ann. Max Partial Duration Bull. 17B Estimate Systematic Record Probability' Estimate Lower Upper MDNRE Flood Discharge Database Record (at Brown Bridge Dam) MDNR a

72 APPENDIX C STRUCTURES INSPECTION FORM

73 Sabin Structure Daily Report Date: Time Arrival: am pm Time depart: am pm Personnel: Wind: Calm Mild Moderate Strong Steady Gusty Direction (from) Speed: mph Temperature: F Precipitation: inches Time: am pm Headpond Elevation: ft ft Tailwater Elevation: ft Time: am pm Time: am pm Change since last reading: USGS Station : Flow: cfs Time: am pm Decreasing Discharge Rate Needed: cfs Discharge Controls: Tainter Gate Powerhouse Stop Logs Auxiliary Spillway Stop Logs Gate Opening (ft) current Change to Debris Steady Increasing Comments Large Turbine Wicket % % Auxiliary Spillway Culverts Other comments: Gate change Notifications Completed: Y N Debris Controls: Inclined Trash Rack: Inspected: Y N Removed debris: Y N Type: Comments: Horizontal Trash Rack: Inspected: Y N Removed debris: Y N Type: Comments: Log Boom: Inspected: Y N Removed debris: Y N Type: Comments: Embankment: Inspected: Y N Erosion Y N Seepage Y N Sloughing Y N If yes, explain (location and details): Comments:

74 Tailrace: Inspected: Y N Debris Y N Erosion Y N Sedimentation Y N Comments: Other Observations: Attach sketches or other information as needed: Attachments: Y N Photographs taken: Y N Unscheduled Follow Up Required: Y N Urgent: Y N Responsible Person: If yes, explain:

75 APPENDIX D SEDIMENT QUALITY DATA SUMMARY

76 Final Report: Boardman River Ponds May 2, 2011 Page 1 of 15 FINAL REPORT BOARDMAN RIVER PONDS SEDIMENT SAMPLING, ANALYSIS AND DATA COMPARISON Prepared for: Grand Traverse Band of Ottawa and Chippewa Indians GLEC Project No: Prepared by: 739 Hastings Street Traverse City, MI Principal contact: Dennis J. McCauley Phone: Fax: dmccauley@glec.com May 2, 2011

77 Final Report: Boardman River Ponds May 2, 2011 Page 2 of 15 Introduction and Methods The upper three dams on the Boardman River, forming Sabin, Brown Bridge and Boardman Ponds, are no longer licensed for hydropower generation and the current owners, the City of Traverse City, Grand Traverse County, and others, are pursuing funding for their removal. In accordance with the Boardman River Dams Settlement Agreement, to which the Grand Traverse Band of Ottawa and Chippewa Indians (GTB) is party, the Boardman River Dams Implementation Team (IT) is responsible for the oversight and coordination of a drawdown and removal plan. GTB in coordination with the IT contracted Great Lakes Environmental Center, Inc. (GLEC) to conduct 1) sediment sampling and analysis in each of the three ponds, 2) a partial Brown Bridge Pond bathymetric survey, 3) comparison of data to established sediment quality guidelines, and 4) comparison of data to previous study data (ECT, 2009). The sediment sampling from the three ponds was designed to satisfy the regulatory requirements of the Michigan Department of Natural Resources and Environment (MDNR-E), while complying with U.S. Army Corps of Engineers (USACE) Quality Assurance standards and Dredging Guidance for collecting data required to be incorporated into the required National Environmental Policy Act environmental study (MDNR-E, 2006). The field activities included a bathymetric survey of Brown Bridge Pond, the collection of sediment core and hand-held Ponar dredge samples which were sent to RTI Laboratories for analysis of metals, PAHs, PCBs, organochlorine pesticides, TOC and percent moisture. GLEC completed the analysis for grain size. Grain size analysis was completed on a composite sample of each core sample rather than individual analysis at discrete depths of each core sample. A cursory qualitative evaluation of grain size at discrete depths for each core sample collected from Brown Bridge Pond may be made by viewing the photographs of each core sample (attached separately). Sediment samples were collected from fourteen sites on Brown Bridge Pond, six sites on Boardman Pond and six sites on Sabin Pond. The primary sampling coordinates for this effort matched those from the 2005 sampling reported in the Boardman River Feasibility Study A Report on Boardman River Existing Sediment Chemistry Data (ECT January 2009). The original sampling point name designations were maintained when possible (e.g., BBP1) and new sampling locations were designated as a combination of the historical notation and a GLEC numbering system (e.g., BBPGLEC1). Additional samples were collected from secondary sites and held as backups, pending interpretation of the primary analytical results. Brown Bridge Pond The sediment sampling plan for Brown Bridge Pond was established using sampling and transect points created by combining map imagery interpolation with coordinates provided in the ECT report (ECT, 2009). The coordinates BBP1 through BBP6 from the ECT report were used to draw transects and establish parallel lines for transects drawn on

78 Final Report: Boardman River Ponds May 2, 2011 Page 3 of 15 single BBP points and for transects drawn on secondary points BBPGLEC1 through BBPGLEC6. The BBPGLEC points were created by interpreting a 2006 Michigan GeoRef DOQQ aerial image of Brown Bridge Pond in ArcGIS. The coordinate data for point BBP3 from the ECT report was discarded as incorrect and a new BBP3 point was created from photo interpretation. Transect shore points t1 through t15 were also created through photo interpretation. Bathymetric surveys were completed along each of these transects. The coordinate outputs for all transect and sampling points were provided to the GLEC field crew as GPS waypoints for the sampling survey. The survey planning map is shown in Figure 1.

79 Final Report: Boardman River Ponds May 2, 2011 Page 4 of 15 Figure 1. Brown Bridge Pond survey planning map (based on pre draw-down water elevations).

80 Final Report: Boardman River Ponds May 2, 2011 Page 5 of 15 The field sampling survey was conducted during late fall, While following the sampling plan, GLEC s survey crew established new sampling points and transect data that accommodated current field conditions. The resultant sediment sampling points and map coordinates and the shoreline coordinates associated with each transect are provided in Table 1. Figure 2 displays both 2010 sampling and transect coordinates using April 2010 DOQ imagery acquired from Grand Traverse County. Table 1. Brown Bridge Pond (BBP) Sediment Sampling Locations and Transect Information (2010 sampling). Transect ID Bank Transect Shore Point ID Latitude (decimal degrees) Longitude (decimal degrees) BBPT1 South t1a North t1b BBPT2 South t2a North t2b BBPT3 South t3a North t3b BBPT4 South t4a North t4b BBPT5 South t5a North t5b BBPT6 South t6a North t6b BBPT7 South t7a Sample Point ID Latitude (decimal degrees) Longitude (decimal degrees) Water Depth (ft) Core Lnth. (in) 1 BBP BBP BBPGLEC BBPGLEC BBP BBP BBPGLEC BBPGLEC BBP BBPGLEC BBP North t7b BBPT8 Delta South t8a Delta North t8b Delta Sediment samples were collected by GLEC using a 4 diameter Vibracore tube.

81 Final Report: Boardman River Ponds May 2, 2011 Page 6 of 15 Figure Brown Bridge Pond sampling locations with 2010 map overlay.

82 Final Report: Boardman River Ponds May 2, 2011 Page 7 of 15 Sample collection on Brown Bridge Pond utilized a pneumatic vibracore unit utilizing 4 diameter cellulose acetate butyrate (CAB) tubing. Core lengths ranged from 10 to 46 inches (Table 1). After collection, the core liners were capped for transport to the laboratory and photographed. Duplicate core samples were collected for a broad scale study being conducted on impoundment sediment modeling by the USACE and Wayne State University. Additional grain size, sedimentation rate and sediment ageing data may be made available from Wayne State as that study is completed. A SONTEC M9 River Surveyor was used to perform a bathymetric survey at each transect on Brown Bridge Pond. This Doppler instrument uses acoustic survey techniques to measure depth. The data generated by the SONTEC M9 was used to create a depth profile graph for each transect. Transect IDs can be found in Table 1, and the depth profiles are shown in Appendix B. Red shaded areas on the depth profiles for transects BBPT7 and BBPT8 show where sonar readings were hindered by thick aquatic macrophyte growth. Boardman and Sabin Ponds The sediment sampling for Boardman Pond and Sabin Pond was also conducted during late fall, A standard Ponar dredge was used to collect sediment for all submerged sites; a hand auger was used at site BP3; site BP3 had become terrestrial since the 2005 study as a result of a recent draw down. Sampling coordinates, depths, sampling times and sediment descriptions can be found in Tables 2 and 3. Figures 3 and 4 display the sampling points on April 2010 DOQ imagery from Grand Traverse County. Table 2. Description and Summary of Boardman Pond Sediment Sampling Locations Conducted by GLEC in Site ID Water Depth (ft) Latitude (decimal degrees) Longitude (decimal degrees) Description BP Dark brown, silt with no odor. BP BP BP BP BP Dark brown silt mixed with some macrophytes (Elodea sp.). Collected by hand auger, in marshy area, to a depth of 0.5m. Soft wet vegetation mat over black silt/muck with no odor. Groundwater springs actively flowing in two nearby locations. Dark brown sand with no odor. Burrowing mayflies and leaches noted in the sediment sample. Dark brown sand and silt mix with no odor. Macrophyte beds up to 1 meter deep covering the entire substrate. Collection site is just offshore of an island created by the pond drawdown, thick macrophyte beds surround black muck/silt.

83 Final Report: Boardman River Ponds May 2, 2011 Page 8 of 15 Table 3. Description and Summary of Sabin Pond Sediment Sampling Locations Conducted by GLEC in Site ID Water Depth (ft) Latitude (decimal degrees) Longitude (decimal degrees) SP SP Description Black silt with small amount of sand, sulfur odor. Site is in a large backwater area with 1 2 feet of soft silt over a firm sandy bottom. Black sand/silt mix with no odor. Sample taken mid channel in quickly flowing water between clumps of SP Black silt with some sand. Sample taken mid channel. Bottom covered in macrophytes (chara) and filamentous algae. SP Very fine black silt with sulfur odor. SP SP Dark brown sand with no odor. Sample taken at the edge of a large sand bar exposed by water draw down. Black sand/silt mix with fishy odor. Sample taken mid channel in quickly flowing water.

84 Final Report: Boardman River Ponds May 2, 2011 Page 9 of 15 Figure Boardman Pond sampling locations.

85 Final Report: Boardman River Ponds May 2, 2011 Page 10 of 15 Figure Sabin Pond sampling locations.