Ingram Gulch Drainage 30% Design Report

Transcription

1 Ingram Gulch Drainage 30% Design Report Submitted to: Four Mile Watershed Coalition Project Number: Date: March 13, 2017 Norwest Corporation 950 South Cherry Street, Suite 800 Denver, Colorado (303) Author:

2 Table of Contents 1 GENERAL LOCATION AND DESCRIPTION Site Location Description of Property DRAINAGE BASINS AND SUB-BASINS Major Drainage Basins Minor Drainage Basins DRAINAGE DESIGN CRITERIA Regulations Drainage Studies, Master Plans, Site Constraints Hydrology Curve Number Method Hydraulics Water Quality Enhancement CHANNEL DESIGN General Concept Energy Dissipation Details Cascade-Step-Pool Sequence Riffle-Step-Pool Sequence Grade Control Structures Toe Wall Structures Reach Details Reach Reach Reach Reach Reach Construction Details Additional Permitting Requirements General REFERENCES APPENDIX A HYDROLOGIC CALCULATIONS AND DESIGN DRAWINGS... A-1 APPENDIX B REFERENCE MATERIALS... B-1 APPENDIX C ECOLOGICAL CHARACTERIZATION REPORT... C-1 APPENDIX D INGRAM GULCH RESTORATION PLANNING AND DESIGN: GEOMORPHOLOGY REPORT. D-1 APPENDIX E ADDITIONAL SITE CHARACTERIZATION REPORTS... E-1 Ingram Gulch Drainage 30% Design Report TOC-1

3 1 GENERAL LOCATION AND DESCRIPTION 1.1 Site Location This drainage report summarizes the existing drainage conditions and the proposed drainage structures from development of the proposed channel improvements in the lower portion of Ingram Gulch located approximately 1/2 mile west of Salina, Colorado near the intersection of Ingram Gulch Road and Gold Run Road in Boulder County, Colorado. The proposed channel improvements include channel grade structures, channel widening, channel and bank stabilization, and installation of riparian and upland vegetation. The project life is approximately 1 year, and the disturbed portion of the channel area will change as the project progresses. A site location map is presented in Figure 1 in Appendix A. 1.2 Description of Property The Ingram Gulch drainage consists of approximately 286 acres of land, of which approximately 270 acres were severely disturbed by fire in Following the fire, in September 2013, severe flooding occurred which significantly affected the Ingram Gulch channel and the downstream drainage Gold Run Creek. Although significant post-fire restoration took place including aerial seeding and mulching, check dams in the upper gulch, a sedimentation pond and debris racks, the area sustained significant flooding in 2011 and 2012 and all treatments were severely impacted or destroyed by the 2013 flood. The project site is divided into two sections. The Lower Gulch is defined as from the intersection of Gold Run Road to the area above the home in the Gulch (approximately 1,700 lineal feet). The Upper Gulch is from above the home upstream to an old mining road that that can access the inchannel tailings/waste rock (approximately 1,300 lineal feet). The property occupies the rugged hills of the Rocky Mountains, consisting of mountainous terrain with an incised canyon or gulch. Ingram Gulch Drainage 30% Design Report 1-1

4 2 DRAINAGE BASINS AND SUB-BASINS 2.1 Major Drainage Basins The Ingram Gulch watershed is located above the Gold Run drainage which is tributary to Fourmile Canyon Creek. Fourmile Canyon Creek flows east into Boulder Creek which flows eastnortheast and ultimately joins the South Platte River upstream from Milliken, Colorado. The project area is within the Fourmile Creek Watershed Master Plan area, and this project supports the goals established in that plan (Michael Baker International, 2014). The Ingram Gulch watershed has a hydraulic length of approximately 9300 feet with a maximum elevation of 8550 msl and a total drainage area of approximately 0.44 square miles. The Federal Emergency Management Agency (FEMA) Flood Mapping has not designated Ingram Gulch as a special flood hazard area. 2.2 Minor Drainage Basins For the project, the watershed area has been delineated into minor drainage basins that correspond with flows to each of the proposed drainage structures. Surface water will be conveyed down channel and where possible avoid residence and associated structures. Control of sediment and flow volumes will be accomplished through the use of channel configuration, overall grade, and as needed, energy dissipation structures. Existing conditions The existing hydrologic conditions were analyzed to allow determination of current condition peak flows. The analysis methods were consistent with Boulder County drainage requirements for each watershed. Watershed boundaries were delineated at the Gold Run Road crossing and the mouth or crossing locations on tributaries to Ingram Gulch. These watershed boundaries are presented on Figure 3 in Appendix A. The Ingram Gulch channel is highly disturbed from the historic mining and recent fire, flooding, and emergency repairs. According to the Fourmile Creek Watershed Master Plan, and confirmed by site inspections: The high flows combined with the extended duration of the event and sediment/debris inputs from landslides/debris flows resulted in dramatic changes in the creek corridor and significant infrastructure damage, both public and private. The watershed experienced stream migration, in-stream and off- Ingram Gulch Drainage 30% Design Report 2-1

5 channel deposition and erosion, loss of riparian ecological function, and destruction or significant damage to homes, roads, embankments, bridges, and other infrastructure (Michael Baker International, 2014). The impacts from these disturbances result in unstable site conditions, and a reference reach could not be identified within the Ingram Gulch watershed. Similar disturbances have occurred in nearby watersheds; therefore, the existing conditions cannot be used as a guide for designing the restored channel. The key feature of the stream channel is the steep gradient, which is typically greater than 10%. Sinuosity is essentially non-existent with sinuosity values less than The channel is moderately incised with entrenchment ratios up to However, these conditions are primarily due to the post-flood recovery efforts to re-establish access to the drainage. Thus, the channel morphology for the project area is Rosgen Classification Aa+. Select areas have lower gradients and therefore different Rosgen Channel types. A detailed discussion of the channel geomorphology is provided by Ottertail Environmental, Inc. in Appendix D. Energy dissipation is key to controlling erosion. Channel reaches above the residence and immediately near the mouth of the watershed have been eroded to bedrock; these reaches exhibit stability due to the presence of the bedrock. The channel bed material consists of a well-graded sand, gravel, and cobble material, which appears to be stable under low-flow conditions. However, due to the channel gradient, this material would not be stable during high flows following a modest storm event such as the 2-yr or 5-yr event. More importantly, erosion of the channel side slopes has undercut the valley walls, and these are unstable regardless of the flow conditions. These unstable slopes continue to erode, and sediment transport will be enhanced during any flood flows. Vegetation is limited or non-existent along the riparian corridor. Besides vegetation being damaged or removed during the flooding, the unstable slopes prevent any vegetation from growing in these areas. The channel system requires stabilization of the valley walls and channel side slopes, additional bed stabilization and energy dissipation, and establishing riparian vegetation for there to be a functioning stream corridor. Additional studies within the Ingram Gulch watershed have been conducted as part of this project, and the results of these studies are included in Appendix E. Key studies include the macroinvertebrate investigation and report provided by Ottertail Environmental, Inc. and the debris flow potential report provided by the Colorado Geological Survey with an interpretation of the results and mitigation design provided by Norwest Corporation. Ingram Gulch Drainage 30% Design Report 2-2

6 3 DRAINAGE DESIGN CRITERIA 3.1 Regulations Drainage channels were analyzed and designed following the guidelines established Boulder County Storm Drainage Criteria Manual (BCSDCM, 2012). Applicable tables, figures, and charts from these manuals can be found in Appendix B. This report analyzes drainage structures for the minor (2-yr, 5-yr, 10-yr, and 25-yr) and major (50-yr and 100-yr) storm events. 3.2 Drainage Studies, Master Plans, Site Constraints There have been a number of studies that have covered the Gold Run drainage. Wright Water Engineers (2011) prepared an evaluation of the post-fire hydrology for the Fourmile Canyon area. In 2013, the Colorado Department of Transportation (CDOT) started development of new hydrologic models in the watersheds affected by the September 2013 floods, of which Gold Run drainage was one. The peak discharge values developed were presented in the Michael Baker (2014) Boulder Creek Study. Additionally, hydraulic modeling for Gold Run channel was based off the Fourmile Creek Watershed Master Plan dated December 12, Also, the FEMA Flood Insurance Study (FIS) for Boulder County, dated December 18, 2012, Included the Gold Run drainage in evaluating the downstream areas. 3.3 Hydrology The watershed areas of the sub-basins are presented on Figure 3. This topography was developed from the 2013 post-flood LiDAR data and a 2016 aerial survey of the channel area of the Gulch. These data were combined to provide a current representation of the channel and watershed. The subwatersheds range from acres in the eastern basin to over acres for the upper reach of the main channel. As the overall drainage area was more that than 100 acres in area, the curve number method was used to determine the peak flows. This method is discussed in detail below Curve Number Method Design of the channels and calculation of run off quantities were carried out using HEC-HMS Version 4.2, a publicly available software package that calculates the runoff response to a given precipitation event for specific surface topography, soil, and vegetative cover conditions using subroutines from TR-55 (USDA-SCS, 1986). Application of the HEC-HMS program involves subdividing the drainage area into sub-watersheds with relatively uniform surface characteristics. Output of the curve number method flow calculations are included as Appendix A. Ingram Gulch Drainage 30% Design Report 3-3

7 Site Precipitation In accordance with county regulations, the 2-year, 5-year, 10-year, 25-year, 50-year, and 100- year, 2-hour storms were utilized in the hydrologic analyses. The rainfall distribution for the 2- hour storms were determined from Table 502 in the BCSDCM (Attached in Appendix B). Incremental rainfall depths were entered into the HEC-HMS time-series data files for each duration storm. Site Runoff The SCS Curve Number method was used to determine peak flows and runoff volumes from the various watersheds. The area, curve number (CN), and the watershed lag time (derived from time of concentration) were determined for each of the watersheds and entered into the HEC- HMS model. Areas were determined for each watershed from the topographic map of the drainage. Watershed CN values were determined by dividing each watershed into various land use categories based on vegetation cover. Land use categories for vegetated areas were obtained from TR 55 Tables 2 2 a through d in the HEC HMS Technical Reference Manual, March 2000 (Appendix B). Also, specific relationship CN values for developed areas were determined from Table 9.5 of Part 630, National Engineering Handbook, Chapter 9 (NRCS, 2004). These are presented in Appendix B. A curve number of 82 was assigned to bare soils and open, unvegetated areas. A CN of ranging from 52 to 59 was used to represent the runoff response from vegetated areas on the natural hillsides and assuming a C hydrologic soil type. This soil type assumes the soil has a silty sandy texture with limited infiltration potential. After a curve number is determined for each land use area within each subbasin, a composite curve number was calculated based on the formula below: From this, a weighted curve number was calculated for each watershed that was comprised of a mix of these cover conditions. The curve number calculations are listed in Table 3.1. Ingram Gulch Drainage 30% Design Report 3-4

8 Upper Mainstem Table 3.1 Subwatershed Areas and Curve Number Calculations NW Central Basin NE Central Basin NE Sidestem Lower Sidestem Middle Mainstem Eastern Basin Lower Mainstem Watershed Vegetated Area (ac) Vegetated Curve Number Unvegetated Area (ac) Unvegetated Curve Number Weighted Curve Number Sub-Watershed Area (ac) The time of concentration values were determined using the SCS method described in Part 630, National Engineering Handbook, Chapter 15 (NRCS, 2010). The following equations determine both the Lag Time and the Time of Concentration values: and where: L = Lag, h Tc = Time of Concentration, h L = Floe Length, ft Y = Average Watershed Land Slope, % S = Maximum Potential Retention, in CN = Curve Number Ingram Gulch Drainage 30% Design Report 3-5

9 An assumption of 10% impervious area was designated for all the watersheds. Table 3.2 presents the Time of Concentration and Lag time results. Upper Mainstem NW Central Basin NE Central Basin Table 3.2 Lag Time Calculations NE Sidestem Lower Sidestem Middle Mainstem Eastern Basin Lower Mainstem Watershed ID Maximum Elevation (ft) Minimum Elevation (ft) Sub-Watershed Slope (%) Hydraulic Length (ft) Time of Concentration (hr) The model results listed in Table 3.3 present the peak flows from the mouth of Ingram Gulch for the various rainfall return periods. These values were used for design purposes. Table 3.3 Model Peak Flow Results Return Period (Years) Peak Flow (cfs) Runoff Volume (Ac-ft) Hydraulics The channel hydraulics were evaluated for the various flow results. The standard design for Boulder County is the 10-yr, 2-hr event. However, for this project, Norwest used the 25-yr, 2-hr Ingram Gulch Drainage 30% Design Report 3-6

10 event to provide additional protection for the restored channel. The channel design and erosion protection is designed to meet the requirements of the 25-yr, 2-hr storm event. 3.5 Water Quality Enhancement The project will protect water quality in Ingram Gulch and Gold Run by stabilizing the channel and minimizing the potential for erosion. There are multiple open mine workings with flowing water and multiple piles of mine waste rock, and there have been no attempts to mitigate water quality impacts (if any) by mine waste or mine drainage within the Ingram Gulch watershed. Ingram Gulch Drainage 30% Design Report 3-7

11 4 CHANNEL DESIGN 4.1 General Concept Flows in Ingram Gulch will be conveyed to Gold Run by stabilizing the Ingram Gulch Channel from above the private residence to the confluence of Ingram Gulch and Gold Run. This stream segment has been split into five reaches for design purposes, and these reaches are based on changes in the channel gradient or the presence of existing structures in or near the channel. The channel will be stabilized using geomorphic principles to establish a functioning riparian corridor and promote wildlife habitat. Minor changes to the stream alignment are proposed where it is necessary to provide the necessary channel geometry, but the majority of the channel will remain at its current location. Similarly, there will be localized adjustments to the stream profile to place grade control and energy dissipation structures, but most of the channel will remain at is current grade. A debris rack is proposed for the uppermost extents of the design area to mitigate impacts from debris flows. This debris rack will not decrease flood flows, as there is not sufficient containment capacity due to the steam channel gradient. Revegetation plans including plant palettes and seed mixes for the various hydroseres present in the lower Ingram Gulch drainage are included in Figure 15 in Appendix A, and a discussion of the revegetation plans are included in the Ecological Characterization included in Appendix C. Each of the designs are discussed below in Sections 4.2 and 4.3, and the design drawings are attached in Appendix A. 4.2 Energy Dissipation Details Ingram Gulch has a steep gradient of approximately 13%, and energy dissipation structures are required for most of the channel. Cascade-step-pool sequences are used where the channel gradient exceeds 15%, riffle-step-pool sequences are used where the channel gradient ranges from 8% to 15%, and grade control structures are used where the channel gradient is less than 8%. Toe wall structures are used where the valley wall has been eroded by the stream and is oversteepened and unstable. These structures and their locations are discussed below. Design details for each structure are adapted from Stream Mechanics (2013) and are included in Figure 14 Appendix A Cascade-Step-Pool Sequence Cascade-Step-Pool sequences occur along channel segments steeper than 15% and contain a complex network of riverine features constructed with large bed material. The cascade is characterized by a series of small steps and small pools forming the steep channel gradient. The step is a short, near-vertical drop into a plunge pool. The small pools within the cascade have minimal depths and are not effective at dispersing energy; consequently, the larger plunge pools Ingram Gulch Drainage 30% Design Report 4-1

12 are required for energy dissipation. This pattern is repeated along the length of the steep channel segment. The cascade/small pool and step portions are typically 70% of the feature length, and the larger pool is approximately 30% of the feature length. The larger plunge pools are typically spaced at distances of 1 to 3 times the bankfull width. The channel bed material consists of well graded material with stone sizes ranging from boulders to sand. The largest stones in the channel bedding material are resistant to design flows and form the cascade drops and the step drops. The medium to smaller stones provide materials suitable for aquatic organisms and form the small and large pools. A schematic of a typical Cascade-Step-Pool sequence is included in Figure 14A in Appendix A Riffle-Step-Pool Sequence Riffle-Step-Pool sequences occur along channel segments with gradients between 8% and 15% and contain a complex network of riverine features constructed with medium-sized bed material. The riffle is characterized by an oversteepend channel segtment which may contain a series of small drops and micro-pools. The step is a short, near-vertical drop into a plunge pool. The micro-pools within the riffle have minimal depths and are not effective at dispersing energy; consequently, the larger plunge pools are required for energy dissipation. This pattern is repeated along the length of the channel segment. The riffle and step portions are at least 80% of the feature length, and the plunge pools are approximately 20% of the feature length. The plunge pools are typically spaced at distances of 1 to 5 times the bankfull width. The channel bed material consists of well graded material with stone sizes ranging from boulders to sand. The largest stones in the channel bedding material are resistant to design flows and form the riffle structures and the step drops. The medium to smaller stones provide materials suitable for aquatic organisms and form the pools. A schematic of a typical Riffle-Step-Pool sequence is included in Figure 14A in Appendix A Grade Control Structures Grade control structures occur along channel segments with gradients less than 8% and consist of boulder sills placed at the channel invert elevation to prevent or limit vertical drops in the channel profile. Erosion control is primarily provided by channel vegetation, and the grade control structures are used to limit erosion to localized areas between the rock sills should the vegetation be overwhelmed. The channel bed material consists of well graded material with stone sizes ranging from boulders to sand. The largest stones in the channel bedding material are resistant to design flows and form the sills structures. The medium to smaller stones provide materials suitable for aquatic organisms and form the channel bed. A schematic of a typical grade control structure is included in Figure 14A in Appendix A. Ingram Gulch Drainage 30% Design Report 4-2

13 4.2.4 Toe Wall Structures Toe wall structures are included where the valley slopes are oversteepened and in need of stabilization. The toe walls consist of boulders stacked to the desired height with compacted fill placed between the boulder and the valley wall. The toe wall is sloped towards the valley wall to compensate for geotechnical forces from the fill material. The slope above the toe wall may either be placed in soil lifts or occur as a sloped fill. Regardless, the slope is covered with an erosion control blanket and revegetated. Schematics of toe wall structures, soil lifts, and sloped fill are included in Figure 14A in Appendix A. 4.3 Reach Details Lower Ingram Gulch has been split into five reaches for this project based on channel gradients and existing features near or in the channel. Modifications in each reach include the addition of a low-flow channel that is 4 to 6 inches deep and approximately 18 inches wide. This channel will convey perennial flows and runoff from very small storm events. Outside the low-flow channel is the bankfull channel, which is approximately 8 feet wide and sloped towards the lowflow channel at 2% to 5%. The bankfull channel will convey runoff from the 2-yr storm and greater. Wherever possible, a floodplain The designs for each reach are discussed below. Maps showing the channel and floodplain modifications, channel profiles, and channel cross-sections for each reach are included in Appendix A Reach 1 Reach 1 is at the mouth of Ingram Gulch and extends from station 0+00 to The channel slopes range from 8.6% to 16.5%. The canyon narrows at the lower extend of Reach 1. This and the private driveway results in a decreased channel width, which has cause undercutting and oversteepening of the hillside on the west side of the channel. To address this erosion, the Reach 1 design includes moving the stream channel east by approximately 5 feet and using this space to replace fill at the toe of the slope. A rock boulder wall is proposed between the driveway and the channel to maintain at least a 12-foot driveway width and the necessary channel width. A rock boulder wall is also proposed on the west side of the channel to buttress the oversteepened valley wall. A fill slope is placed above the boulder wall. Each fill slope will be placed in compacted lifts at a gradient of 1.5H:1V until the existing topography is reached (approximately 10 feet above the existing channel elevation). Native riparian or upland vegetation will be planted in all disturbed areas. The locations of the channel modifications are shown on Figure 4, and the reach profile and cross-sections are shown on Figure Reach 2 Reach 2 is characterized by a slightly wider and less-steep valley and extends from station 3+64 to The channel slopes range from 5.4% to 11.7%. The undercutting and oversteepening Ingram Gulch Drainage 30% Design Report 4-3

14 of the hillside on the west side of the channel continues through the southern half of Reach 2. To address this erosion, the design includes placing a boulder wall at the toe of the slope and placing compacted fill lifts at a gradient of 1.5H:1V. The east side of the channel contains a gently sloping hill that will be excavated to create a floodplain. The floodplain will be sloped towards the channel at 2% to 5%, and logs will be partially buried on the floodplain to increase flow resistance. A rock boulder wall is proposed between the driveway and the floodplain to maintain at least a 12-foot driveway width and a vegetated floodplain. Native riparian or upland vegetation will be planted in all disturbed areas. The locations of the channel modifications are shown on Figure 6, and the reach profile and cross-sections are shown on Figure Reach 3 Reach 3 starts at the culvert outlet below the private residence and extends from station 6+06 to The channel slopes range from 3.7% to 18.8%. The existing channel requires little work throughout Reach 3, and the primary channel modifications are to provide channel stabilization and energy dissipation. In addition to the channel stabilization measures discussed in Section 4.2, a plunge pool will be placed at the culvert outlet to dissipate energy and to remove the vertical drop between the culvert and the channel. The floodplain and boulder wall between the channel and the driveway extends from Reach 2 into Reach 3. Also, a boulder wall is necessary to stabilize the valley slopes. Compacted fill will be placed in lifts at a gradient of 1.5H:1V above the boulder walls. Native riparian or upland vegetation will be planted in all disturbed areas. The locations of the channel modifications are shown on Figure 6, and the reach profile and cross-sections are shown on Figure Reach 4 Reach 4 includes the existing sediment basins and related outlet pipes. Reach 4 extends from station 9+36 to Channel modifications in this reach are required to increase the flow capacities from the two upper sediment basin outlet works. Each sediment basin contains outlet pipes, but these are not sufficient to convey the design flows, and emergency spillways are proposed at each location. The sediment basin walls are mostly protected with boulder walls, but additional boulders are necessary at select locations to protect the entirety of the sediment basins. The culvert under the driveway can safely convey the design flows and no channel modifications are proposed. Native riparian or upland vegetation will be planted in all disturbed areas. The locations of the channel modifications are shown on Figure 8, and the reach profile and cross-sections are shown on Figure 9. Details on the spillway designs are included in Figure Reach 5 Reach 5 includes the channel above the private residence and extends from station to A debris rack is proposed at station 14+00, and this feature will trap debris and sediment Ingram Gulch Drainage 30% Design Report 4-4

15 without detaining water. The rack height at the centerline is approximately 10 feet. It is anchored at the bottom using a 3-ft tall concrete block, and it is anchored at the valley walls using an earthen berm. A 12-inch pipe located at the channel invert elevation will allow conveyance of stream flows. A rack at the culvert inlet will prevent culvert plugging while allowing retention of the debris and sediment. The debris rack will maintain a channel bottom width of 10 feet to allow the conveyance of flood flows. This structure is intended to collect large sediment, and there will be no flood dissipation from this structure. Also, fine sediment consisting of sand and gravel will continue to flow downstream from this structure. Boulder walls and energy dissipation structures will be constructed in the channel below the sediment detention basin to stabilize the channel and prevent continued erosion of the valley walls. Above the debris rack, the stream channel has incised to bedrock and appears to be stable. Only planting of riparian vegetation is planned for this area above station Native riparian or upland vegetation will be planted in all disturbed areas. The locations of the channel modifications are shown on Figure 10, and the reach profile and cross-sections are shown on Figures 11a and b. Details on the spillway designs are included in Figure Construction Details Construction of the lower gulch is planned for the summer of 2017 as soon as permitting, detailed designs, and contracting with a construction company are completed. Considering the project schedule and time constraints, construction is expected to start in mid to late June and extend through September. Construction activities will commence with the mobilization of equipment, materials, and supplies. These will be staged along existing site roads and pads as shown in Figure 16. Areas planned for restoration are typically adjacent to site roads and can be accessed using these roads. Reaches not accessible using the existing road network will require construction of temporary access roads. These temporary roads will follow the stream corridor, and they will be converted to the restored stream channel by retreating up the temporary road while constructing the channel. Construction will occur following peak flows associated with spring runoff, and Ingram Gulch is expected to have either dry conditions or minimal flow (which can be diverted with a pipe). These dry or nearly dry conditions will enhance construction productivity and, with the use of best management practices (BMPs), minimize sediment loading to Ingram Gulch and Fourmile Run. During construction, disturbance areas will be limited to minimize the need for BMPs to a focused area. Grading, berming, earth dikes, drainage swales, silt fencing, inlet protection, and other BMPs will be used for sediment control. Upon completion of construction, all disturbed areas will be vegetated from seed or container stock. Also, any disturbed areas or stockpiles that will be left inactive for over 30 days will be seeded to minimize erosion. The construction contractor will be responsible for watering seeded and planted areas for the summer and fall following construction, and Fourmile Watershed Coalition will be responsible for watering Ingram Gulch Drainage 30% Design Report 4-5

16 in subsequent years if necessary. All slopes steeper than 3H:1V will be stabilized with erosion control fabric. The project consists of restoring approximately 1700 lineal feet of stream channel along the lower extents of Ingram Gulch. The disturbance and revegetation area is approximately 2.4 acres. The total excavation volume is approximately 1540 cubic yards, and the total fill volume is approximately 1250 cubic yards. Much of the material excavated can be used for project fill material, but materials with specified sizes (i.e. boulders and bedding material) must be imported. Approximately 500 cubic yards of boulders and bedding material will be imported. Additionally, approximately 80 cubic yards of boulders and 9 cubic yards of concrete are required for armoring and securing the debris rack. These materials are placed above the existing grade, and they do not impact the materials balance. There are approximately 800 cubic yards of excess material, and this material can be used onsite to backfill open areas on the property but not related to the stream restoration. These areas are the staging areas displayed on Figure 16. There is a cemetery located on the west side of Ingram Gulch approximately at station This area will not be disturbed, and an archeologist will be onsite when constructing in this area as required by the State Historic Preservation Office. The cemetery is the only known limited impact special use criteria in the project area. 4.5 Construction Cost Estimate Construction of the lower Ingram Gulch restoration project will occur as a series of small excavations and fills along the 1700 feet of channel. Also, access to the project work areas is limited to single lane roads. The nature of these small volumes and limited access suggests that the work will be performed relatively inefficiently, which results in higher unit costs. Norwest has estimated construction volumes and costs for the various tasks, and these are listed in Table 4.1. This cost estimate is based on construction volumes calculated from the 30% design drawings and unit costs from CostWorks 2017 and RS Means The unit costs were selected for each construction task that best represented the work at Ingram Gulch and include adjustments for location (Boulder County, Colorado), crews required for each task, contractor overhead and profit, and for inflation. The unit costs were also adjusted by Norwest to better represent the expected daily production for each task based on the project constraints. Ingram Gulch Drainage 30% Design Report 4-6

17 Table 4.1 Construction Cost Estimate Construction Volume Units Unit Cost Total Mob/Demob 10 Each $2,672 $26,715 Excavation 1587 cu.yd $12.52 $19,866 Stream Bedding 840 cu.yd $41.69 $35,016 Stream Boulders 400 ton $ $78,191 Boulder Wall 3792 S.F. $ $547,215 Debris Rack 1 Each $101,158 $101,158 Vegetation S.F. $4.16 $321,703 Total na $1,129, Additional Permitting Requirements The project requires drainage approval from Boulder County. The project also impacts Waters of the United States, and an individual 404 permit is required from the US Army Corps of Engineers. 4.7 General Applicable tables, figures, and charts can be found in Appendix B. Ingram Gulch Drainage 30% Design Report 4-7

18 5 REFERENCES Boulder County, Boulder County Stormwater Drainage Criteria Manual. October Boulder, Colorado. Boulder County, Fourmile Creek Watershed Master Plan. December, British Columbia, Debris Flow Control Structures for Forest Engineering. British Columbia Ministry of Forests Research Program. FEMA, Flood Insurance Study (FIS) Boulder County, Colorado and Incorporated Areas. Effective Date: March 18, Federal Emergency Management Agency. Michael Baker International, Drainage Study Gold Run Drainage. August Boulder, Colorado. Michael Baker International, Fourmile Creek Watershed Master Plan. December 12, Boulder, Colorado. NOAA, NOAA Atlas 14 Precipitation-Frequency Atlas of the United States Volume 8 Version 2.0: Volume 8 Version 2.0: Midwestern States (Colorado, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma, South Dakota, Wisconsin). U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Silver Spring, Maryland. (accessed January 19, 2016). Stream Mechanics, Design Criteria for Restoring Headwater Mountain Streams. Presented at the 2013 Mid-Atlantic Stream Restoration Conference. Baltimore, Maryland. USDA Soil Conservation Service, Urban Hydrology for Small Watersheds: Technical release TR-55, USDA Soil Conservation Service, Washington. 164p. Wright Water Engineers, Memo to Boulder County Transportation on Post-Fire Hydrology. February Denver, Colorado. Ingram Gulch Drainage 30% Design Report 5-1

19 Appendix A Hydrologic Calculations and Design Drawings Ingram Gulch Drainage 30% Design Report A-1

20 Appendix B Reference Materials Ingram Gulch Drainage 30% Design Report B-1

21 Appendix C Ecological Characterization Report Ingram Gulch Drainage 30% Design Report C-1

22 Appendix D Ingram Gulch Restoration Planning and Design: Geomorphology Report Ingram Gulch Drainage 30% Design Report D-1

23 Appendix E Additional Site Characterization Reports Ingram Gulch Drainage 30% Design Report E-1