JHI Sweetheart Lake: Spawning Habitat Assessment & Maintenance

Transcription

1 Technical Memorandum JHI Sweetheart Lake: Spawning Habitat Assessment & Maintenance Date: April 4, 2014 To: Duff Mitchell Company: JHI From: Dan Miller, Lon Mikkelsen, Inter Fluve, Inc. Introduction Juneau Hydro, Inc. (JHI) is preparing a FERC license application for the Sweetheart Lake Hydroelectric Project (FERC No. P 13563). The project would divert flow from the outlet of Lower Sweetheart Lake (57 56ʹ43.25ʺN; ʹ12.57ʺW) through a penstock and power plant before returning flow via tail race to Sweetheart Creek immediately below the barrier falls. One requirement for the project is to maintain existing levels of pink salmon spawning that is present in the Anadromous Reach extending from approximately elevation 15 feet to the proposed tailrace outlet. In order to meet this requirement, JHI will work cooperatively with Alaska DFG to track the area of suitable spawning habitat, and potentially mitigate for a reduction in available spawning habitat area through gravel augmentation. The details of this proposed monitoring and gravel augmentation are presented in detail over the following sections. Changes in flow and sediment supply Two primary factors for suitable spawning habitats include flow conditions (depth and velocity) and suitable sized substrate. Existing stream hydrologic conditions are documented in the Project s Hydrology Report (Civil Science, 2013): Figure 2 shows monthly average flow values up to 670 cfs during the month of June. The monthly average flow for June, July, August and September all exceed 490 cfs. Figure 9 indicates estimated average daily flows commonly exceed 1,000 cfs and a maximum flow exceeding 3,000 cfs Proposed discharges from the Project power house into the tail race and Anadromous Reach may range between 300 to 486 cfs (D. Mitchell, personal communication). After Commercial Operations Date (COD), but prior to reservoir fill levels which will be determined by precipitation for the years immediately following COD, JHI will operate Anadromous Reach inflows to provide minimum flows requested by 4/4/14 JHI Sweetheart Lake 1

2 Alaska DFG in their recommended conditions for Instream Flows for the Sweetheart Creek Anadromous Reach below the tailrace. JHI would operate the project to maintain instantaneous instream flows in the Anadromous Reach of Sweetheart Creek, as measured at the stream gage required by article 4, pursuant to the following schedule: Dates Minimum flow (cfs) measured at gage January February 40 March 45 April 119 May September 330 October 324 November December 117 Sediment transport conditions along the Anadromous Reach will be impacted by the reduction in high flows and associated sediment supply from the Bypass Reach through the Sweetheart Creek canyon. Existing spawning habitats Existing spawning habitats were documented in the Project s Fisheries Study (Aquatic Science, 2012). The existing system has limited observed spawning gravel habitats due to the nature of the high gradient, bedrock pool drop type of channel morphology. The macro pools were observed to be bedrock lined and contain large substrate and boulders unsuitable for spawning. Figure 25B of the Fisheries Study notes spawning substrate being present in a side riffle of the first waterfall, below Macro Pool 2. Section 5.7 of the Fisheries Study describes spawning as likely to occur near the top of the intertidal in the vicinity of transects 1A and 1B on Figure 25B. Spawning habitat assessment and reporting In order to maintain existing levels of spawning, baseline and annual assessments of spawning habitats will be conducted by qualified professionals (e.g. fisheries biologists, fluvial geomorphologists, hydraulic engineers). Within the Anadromous Reach shown in Figure 1, substrate and hydraulic conditions suitable for spawning will be assessed and documented with photos, measurements and pebble counts to track changes in total area of spawning habitat. Alaska DFG may have a representative present at their own expense during the JHI annual gravel assessment. Findings will be documented in a concise report with attached graphics, notes and photos as appropriate to document spawning conditions of that year. A narrative of changes from the prior year conditions will be included. 4/4/14 JHI Sweetheart Lake 2

3 Spawning habitat maintenance At the end of the third year of operations, changes in spawning habitat will be assessed. If it is determined that there is a net reduction in the area of available spawning habitat, a prescriptive plan will be prepared in cooperation with Alaska DFG to take measures to provide a similar level of spawning habitat to baseline conditions. Actions are anticipated to include: 1. Identification of zones with hydraulics suitable for spawning. 2. Augmentation with gravel suitable for spawning. The locations, volumes and size of substrate to be injected into the Anadromous Reach will be developed using assessment findings to inform the proposed prescriptions and in cooperation with Alaska DFG. The location where gravel could feasibly be injected will be partially based on equipment access considerations. A tentative injection location is shown in Figure 2 and would require temporary chutes to deliver gravel to the stream. Assessment and prescriptive spawning habitat maintenance timeline A template for the gravel augmentation program is recommended as follows and summarized in Table For the first 5 years after Commercial Operations Date (COD), spawning habitat assessment and reporting will occur by JHI in the spring. Alaska DFG may have one or more representative(s) present at their own expense during the JHI annual gravel assessment. 2. Within 30 days of the annual assessment, JHI will provide to Alaska DFG a two to three page assessment report documenting results of assessment. 3. On the 3 rd year after COD, JHI and Alaska DFG will meet to review the assessments and determine if: a. there has been a reduction in the area of suitable spawning habitat, and b. a gravel augmentation event is to be prescribed based on the year 3 review. Note: based on the periodicity of salmon species (see Table 9 of the Fisheries Study, 2012), mid May through June appears to be the least obtrusive time to implement a gravel augmentation event. These tentative dates are suggested to comply with Alaska DFG Preliminary Conditioning Item 10 Timing of Instream Activities: Timing windows for instream construction activities and stream crossings shall be established by the Alaska DFG Habitat Biologist assigned to the project. Timing windows will be conditioned in the Alaska DFG issued Title 16 permit. The suggested timing windows are intended to ensure that instream activities do not adversely impact aquatic resources. 4. Upon the 6th and every successive 5th year anniversary of COD, JHI and Alaska DFG will meet to analyze the spawning habitat assessment and prescriptive gravel augmentation program and determine the necessity of continuing these actions for the next five years. 4/4/14 JHI Sweetheart Lake 3

4 References Aquatic Science, November 5, Fisheries Studies at Sweetheart Creek and Sweetheart Lake 2011/2012 Civil Science, September 22, Sweetheart Lake Hydroelectric Project, FERC No Hydrology Report LiDAR data for the Sweetheart Lake project site collected in 2012 by Aerometric, Anchorage, AK USFS Aerial photos 4/4/14 JHI Sweetheart Lake 4

5 Attachments: Figure 1 Spawning habitat study area. Figure 2 Spawning gravel injection location. Table 1 Project timeline. 4/4/14 JHI Sweetheart Lake 5

6 SWEETHEART CREEK PROPOSED TAILRACE SPAWNING HABITAT ASSESSMENT AREA SPAWNING HABITAT ASSESSMENT AREA 22-FT DEEP MACRO POOL 1 SWEETHEART CREEK - ANADROMOUS REACH SPAWNING HABITAT ASSESSMENT AREAS GRAPHIC SCALE (in feet) FIGURE 1 - SWEETHEART CREEK SPAWNING HABITAT ASSESSMENT AREAS

7 GRAPHIC PREPARED AND PROVIDED BY: ALL POINTS NORTH FIGURE 2 - SWEETHEART CREEK SPAWNING GRAVEL INJECTION LOCATION

8 Table 1 Spawning habitat assessment and maintenance timeline Year following COD Reach spawning habitat assessment & report Prescriptive spawning habitat maintenance Spawning gravel augmentation implementation Reassess approach revise as appropriate 0 Conduct baseline assessment of spawning habitat in the Anadromous Reach and provide report to Alaska DFG n/a n/a n/a 1 2 Conduct spawning habitat assessment and provide report to Alaska DFG n/a n/a n/a 3 Conduct spawning habitat assessment and provide report to Alaska DFG In cooperation with Alaska DFG, determine if prescriptive spawning habitat maintenance via gravel augmentation is required and determine details. If required conduct augmentation gravel injection during 2nd week of May for least impact to Steelhead and Pink salmon n/a & each successive 5th year Conduct spawning habitat assessment and provide report to Alaska DFG Conduct spawning habitat assessment and provide report to Alaska DFG Conduct spawning habitat assessment and provide report to Alaska DFG COD: Commercial Operations Date In cooperation with Alaska DFG, determine if prescriptive spawning habitat maintenance via gravel augmentation is required and determine details. In cooperation with Alaska DFG, determine if prescriptive spawning habitat maintenance via gravel augmentation is required and determine details. In cooperation with Alaska DFG, determine if prescriptive spawning habitat maintenance via gravel augmentation is required and determine details. If required conduct augmentation gravel injection during 2nd week of May for least impact to Steelhead and Pink salmon If required conduct augmentation gravel injection during 2nd week of May for least impact to Steelhead and Pink salmon If required conduct augmentation gravel injection during 2nd week of May for least impact to Steelhead and Pink salmon n/a n/a Meet with Alaska DFG to analyze and revise if necessary spawning habitat assessment and maintenance program FERC PDF (Unofficial) 4/8/ :44:20 PM

9 TECHNICAL MEMORANDUM Applied River and Wetland Restoration Founded 1983 Tech Memo Title: To: From: JHI Sweetheart Lake Hydropower Project Bypass Canyon Reach Habitat Suitability Assessment Duff Mitchell, Juneau Hydropower, Inc. Lon Mikkelsen, Inter Fluve, Inc. Date: April 7, 2014 PROJECT UNDERSTANDING Juneau Hydro, Inc. (JHI) is preparing a FERC license application for the Sweetheart Lake Hydroelectric Project (FERC No. P 13563). The project would divert flow from the outlet of Lower Sweetheart Lake (57 56'43.25"N; '12.57"W) through a 9621 foot tunnel and penstock to a power plant before returning flow through a tailrace to Sweetheart Creek at the barrier falls. This study evaluates river conditions and associated habitats required to maintain sustainable populations of various fish species along the Canyon Reach (Sweetheart Creek Bypass Reach) from the lake to upstream of the barrier falls near tidewater. Analysis of frequency of mobilization of spawning sized gravels was completed to evaluate the suitability of spawning habitats as one limiting factor necessary for a sustainable population of fish along the Canyon Reach. Analysis of frequency of mobilization of spawning sized gravels to the anadromous reach was considered. EXISTING DATA Dangerous and inaccessible steep canyons prevent access to the Canyon Reach. The report relied on existing data and imagery for this phase of study. A number of data and studies have been completed by others that were made available and used for this study including: LiDAR topography including the Canyon Reach Various aerial photos Overflight video Hydrology Report (Civil Science, 2013) Offices Nationwide 501 Portway Avenue, Suite 101, Hood Rivr, Oregon

10 FISH HABITAT REQUIREMENTS AND LIMITING FACTORS Fish species documented in the system include Dolly varden (S. malma), Rainbow trout (O. mykiss). Dolly varden are present in the lake, above the study reach, likely a population that established itself during the last ice age. Rainbow trout were introduced to the Sweetheart Lake in 1953 and Additionally, there is an artificial supplementation program for sockeye that is managed for regional residents harvest of adults below the barrier falls by the Douglas Island Pink and Chum (DIPAC) hatchery. Additional detail about the past and future management of this species can be found in the Fisheries Study Report (Aquatic Sciences, 2012). Historical stocking of rainbow (O. mykiss) has created a small population that forages on the stocked sockeye juveniles. Additional detail can be found in the JHI fisheries report (Aquatic Sciences, 2012). Criteria for some habitat necessary for sustainable populations of salmonids can be found in Table 1. In evaluating the potential fisheries resources in the reach, the following functions have been considered: Provision of spawning habitat Provision of rearing habitat Provision of holding habitat during juvenile or adult migration The absence or significant limitation of one or more of these functions would prevent a self sustaining wild origin population from becoming established in the project reach. Based on the available data, analyses were completed to determine if spawning sized sediments are likely to exist and able to persist long enough to be usable by resident fish for spawning (see Hydraulics & spawning gravel mobility section). The study reach likely provides temporary rearing and some limited spawning habitat at low discharges. Due to the confined nature of the channel in the canyon, it is unlikely that adult or juveniles would find adequate flood refuge habitat to persist in the reach during high flows. This reach is sediment supply limited, and due to the characteristics of the watershed, sediment supply comes from the side slopes, and the channel is an expression of bedrock and colluvial material supplied from adjacent hillslope processes (see Geomorphology & Sediment Supply section). The mechanism for fish access to the reach appears largely in the upstream to downstream direction, due to the barrier falls at the bottom of the reach. This lack of upstream fish passage helps explain why populations of salmonids with anadromous life history strategies have not established in the reach. Generally, the study area is a transport reach, in terms of sediment and fish species. Juveniles and adults that migrate downstream from the lake into the canyon may opportunistically find rearing or holding habitat, and potentially some limited spawning habitat. 2 of 7

11 Table 1. Water depth, velocity and substrate size criteria for anadromous and other salmonid spawning (from Bjorn & Riser, 1991). However due to the absence or significantly limitation of the three primary functions (spawning, rearing, migration), it is unlikely that any wild origin, self sustaining populations of resident or anadromous species exist in the study reach. Furthermore, it is unlikely for there to be wild origin populations of adult salmonids that have site fidelity within the canyon, due to lack of fish passage, spawning habitats and sufficient flood refuge habitat during flood flows. Any fish use in the reach is by juveniles or adults from the lake and upstream system during the low flow period. GEOMORPHOLOGY AND SEDIMENT SUPPLY Generally, sediment supply to the canyon reach is very low and is driven by episodic slope failures adjacent to the channel. Sediment supply within the study reach appears to be sourced from small steep ravines and drainages with additional colluvial sources from bedrock and canyon walls. Material composition has not been sampled but based on photographic observation, glacial till and bedrock colluvium appears to be the most likely parent material. The Hydrology Report (Civil Science, 2013) lists watershed drainage area tributary to the barrier falls location of Sweetheart Creek as 36.0 square miles and 34.7 square miles at the outlet of Lower Sweetheart Lake outlet. Sediment delivered by the 34.7 square miles tributary to the lake is trapped and detained in the lake. Flows from the lake carry no sediment into the Canyon Reach. The Canyon Reach conveys full run off flows, but is limited in sediment supply to landslide colluvium from the remaining 1.3 square mile area of watershed. This limited sediment supply, combined with the confined valley and steep slopes of the Canyon Reach create high energy conditions that are efficient in transporting any sediment through the reach to tidewater. Channel bed conditions suggest that there is very low sediment supply, and or that it is driven by episodic slope failures. These conditions are poorly suited for the deposition of appropriately sized gravel sources that fish could successfully and sustainably spawn in. HYDRAULICS AND SPAWNING GRAVEL MOBILITY The mobility of spawning sized gravels was analyzed using existing stream flow hydrology and a hydraulic model prepared by Inter Fluve based on existing LiDAR topography. The results of the hydraulic model were used to estimate the size of particle at the threshold of mobility and associated stream flows. The following paragraphs detail this analysis. 3 of 7

12 Inter Fluve prepared a one dimension hydraulic model of Sweetheart Creek through the Canyon Reach from tidewater to the Lower Sweetheart Lake. The US Army Corps of Engineer s River Analysis System, HEC RAS, one dimensional open channel hydraulic model was used. HEC RAS is the industry standard for one dimensional river modeling. Results are included in the Appendix. The model represents stream geometry with cross sections spaced along the study reach. Model sections were extracted from LiDAR topographic data using a routine in AutoCAD CIVIL3D Each cross section is divided into left overbank, channel and right overbank areas. Based on observations by project engineer and surveyor Max Schillinger (pers comm) the creek extends to the base of the canyon walls with no defined flood terraces. Thus, the break point between channel and overbank areas was approximately set at the toe of canyon walls. Model geometry includes spacing between adjacent cross sections. Hydraulic resistance is estimated using the Manning s n coefficient. Values of channel Manning s n was approximated as and overbank areas approximated as 0.07 based on professional opinion for steep rocky reaches. Stream flows were analyzed and reported by Civil Science (2013). Although return period flood event discharges were not identified from the available analyses, the range of flows reported were accounted for in the HEC RAS model by including: 3, 10, 25, 50, 100, 400, 600, 800, 1000, 2000, and 3617 cfs. Model boundary conditions were set at critical depth at both upstream and downstream ends. HEC RAS results for tractive force (shear) were used to complete an incipient motion particle size analysis to estimate size of particle at the threshold of mobility. Larger particles are expected to remain in place, while smaller particles are expected to be mobilized. Spawning sized gravels for resident trout are 3 inch and smaller. Based on the incipient motion particle size analysis, 0.75 psf shear will mobilize a 2.9 inch particle. Comparison of the 0.75 psf shear value against a lower bound profile plot of shear from HEC RAS results over a range of discharges indicates that: Downstream of station 73+00, there are small areas of stream with shear less than 0.75 psf at 100 cfs flows. For 400 cfs and higher flows, shear exceeds 0.75 psf and would mobilize spawning sized gravels. Upstream of station 73+00, there are small areas of stream with shear stress less than 0.75 psf for 400 and 600 cfs. For 800 cfs and higher flows, shear exceeds 0.75 psf and would mobilize spawning sized gravels. 4 of 7

13 From this hydraulic and sediment mobility analysis, approximately 400 cfs flow will mobilize spawning sized gravels. Examining annual and monthly flow duration curves shown in Figure 12 from Civil Science s Hydrology Report (2013) indicates that on an annual basis: 400cfs is exceeded about 37% of time; 600 cfs about 20% of time, and 800 cfs about 10% of time. Monthly flow durations during fish use months of May through October all have greater flows. By month, 400 cfs is exceeded 90% of the time in July and 97% of the time in September. Spawning gravels will not persist in place for the optimal 2 to 5 year time frame to serve as spawning habitats. However, after hydropower operations commence, the Canyon Reach flows will be reduced to 3cfs plus the natural accretion of the Canyon Reach which represents 3% of the historical gaged flow of Sweetheart Creek (Civil Science s Hydrology Report (2013). Lower bound values of shear generated by the HEC RAS model during higher discharge events were further evaluated. 7.8 inch sized particles would be mobilized at 800 cfs for the steeper reach downstream of station For 1000 cfs, 5.8 inch particles would be mobilized along the reach upstream of Most model cross section along the Canyon Reach have higher to significantly higher values of shear as well as during higher stream flows and will mobilize larger particles. This illustrates the severe conditions of large sized sediments through put along the Canyon Reach at its current range of flows.. Sediment flows will mobilize spawning sized gravels at the lower end of the size spectrum after hydropower operations commence to the anadromous reach of the Sweetheart Creek, albeit at a slower pace dictated by high rain events which affect the accretion of the Canyon Reach. Since its likely that most of the anadromous species spawning occurs lower down in the intertidal area of Sweetheart Creek, the reduction in mobilization of future spawning gravels will have a minimal to no effect on the spawning gravel volume in the intertidal area. The anticipated lower controlled cfs of 300 to 486 cfs of the expected hydropower operations will also reduce the flushing and removal of spawning gravel from the intertidal area that has been historically occurring with high volume cfs flood events. SUMMARY Hydraulic and sediment mobility calculations show that spawning sized gravels are expected to be mobilized frequently during the spawning season for Dolly Varden. The Canyon Reach may provide some limited spawning, rearing and downstream migration habitat to adults migrating downstream from the lake or any juveniles that wash over the lake outlet. Due to the absence or limitation of the three primary functions (spawning, rearing, migration), it is very unlikely that a wild origin population of resident or anadromous species would be self sustaining in the bypass canyon reach. Figure 25B in Aquatic Resource Report (Aquatic Science, 2013) shows that a small area of spawning sized gravel located within a hydraulically sheltered area below the future tailrace return and macro pool 2. It is likely that this volume and size of sediment can be delivered from the Canyon Reach with its reduced hydrology and when this coincides with geologic events in the canyon reach that would supply sediment. 5 of 7

14 REFERENCES Aquatic Science, November 5, Aquatic Resource Studies at Sweetheart Creek and Sweetheart Lake 2011/2012 Aquatic Science, November 5, Fisheries Studies at Sweetheart Creek and Sweetheart Lake 2011/2012 Civil Science, September 22, Sweetheart Lake Hydroelectric Project, FERC No Hydrology Report LiDAR data for the Sweetheart Lake project site collected in 2012 by Aerometric, Anchorage, AK P.Y. Julien, Erosion and Sedimentation US Army Corps of Engineers, River Analysis System (HEC RAS), version USFS Aerial photos 6 of 7

15 APPENDIX HEC RAS model results Incipient motion particle size calculations

16 FERC PDF (Unofficial) 4/8/ :44:20 PM

17

18 Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend WS 3617cfs WS 2000cfs WS 1000cfs WS 800cfs WS 600cfs WS 400cfs WS 100cfs WS 50cfs WS 25cfs WS 10cfs WS 3cfs Ground Main Channel Distance (ft) Elevation (ft) *

19 Shear Chan (lb/sq ft) Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend Shear Chan 3617cfs Shear Chan 2000cfs Shear Chan 1000cfs Shear Chan 800cfs Shear Chan 600cfs Shear Chan 400cfs Shear Chan 25cfs Shear Chan 100cfs Shear Chan 10cfs Shear Chan 50cfs Shear Chan 3cfs FERC PDF (Unofficial) 4/8/ :44:20 PM Main Channel Distance (ft)

20 Shear Chan (lb/sq ft) Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend Shear Chan 3617cfs Shear Chan 2000cfs Shear Chan 1000cfs Shear Chan 800cfs Shear Chan 600cfs Shear Chan 400cfs Shear Chan 25cfs Shear Chan 100cfs Shear Chan 10cfs Shear Chan 50cfs Shear Chan 3cfs FERC PDF (Unofficial) 4/8/ :44:20 PM Main Channel Distance (ft)

21 Tractive Force (Shear, psf) Sweetheart Creek Tractive force and mobile sediment sizes Tidewater Lake River Station (ft) 3cfs 50cfs 100cfs 400cfs 600cfs 800cfs 1000cfs 2000cfs 3167cfs Ds(3.0in) Ds(6.0in) Ds(12in) Ds(18in) Ds(24in) FERC PDF (Unofficial) 4/8/ :44:20 PM

22 Shear Chan (lb/sq ft) Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend Shear Chan 100cfs FERC PDF (Unofficial) 4/8/ :44:20 PM Main Channel Distance (ft)

23 Shear Chan (lb/sq ft) Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend Shear Chan 400cfs FERC PDF (Unofficial) 4/8/ :44:20 PM Main Channel Distance (ft)

24 Shear Chan (lb/sq ft) Sweetheart_Creek Plan: Sweetheart_Ex1 3/12/2014 Sweetheart Ck Thalweg Legend Shear Chan 600cfs FERC PDF (Unofficial) 4/8/ :44:20 PM Main Channel Distance (ft)

25 Shields Incipient Motion Particle Size analysis Ds = To (SG 1)* Gw * T* SG = 2.65 specific gravity of sediment GW = 62.4 unit weight of water, pcf T* = 0.03 dimensionless Shield's number for Gravel/cobble material To Mobile Particle Size, Ds (psf) (ft) (in) (mm)

26 Document Content(s) JHI Spawning Habitat Assess-Maint FERC Final IFI PDF JHI Bypass Reach Tech Memo FERC Final PDF