Lake Seventeen and Little Suction Creek Project Environmental Assessment
Meeting Agenda 1. Project Location and Watershed Area 7. Preliminary Alternatives (4) 2. Project Background 8. Environmental Investigations 3. Current Design Facts 9. Final Product 4. Existing Conditions 10. Outreach 5. Purpose and Need 11. Discussion 6. Previous Investigations
Project Location and Overall Watershed Area Lake 17 Watershed ~19 mi 2 Little Suction Creek Diversion Little Suction Creek Watershed above diversion ~47 mi 2
Rehabilitation project in Fort Belknap Project • Constructed in 1930’s Background • Built by CCC- Indian Division • System has become cultural and historic resource • Dam was damaged during a storm event on September 25, 1986 • Current state of disrepair with multiple breach events and inadequate repairs Repairs Needed to Rehabilitate Dam • New principal spillway conduit • Concrete riser • Rock plunge pool • One-foot lift on the dam for overtop protection
Lak ake 17 Dam General Characteristics Design Fac acts • Lake 17 is created from a curved earthen embankment • The dam is 16.0 feet high, with a top width of 16.0 feet and a top of dam elevation of 3025.50’ • Its outlet works include a riser/barrel principal spillway and earthen auxiliary spillway • The length of the dam at the failure elevation of 3023.1’ is ~750 feet • The valley width for a distance downstream at the failure elevation is ~450 feet • The average valley floor elevation is 3,005.0’ • The existing principal spillway configuration has a flow capacity of 50 cfs when the pool level is at the crest of the auxiliary spillway • When the pool level rises to the top of the embankment, the principal spillway capacity increases to 106 cfs • The auxiliary spillway is a vegetated open channel
Breach at the Little Suction Creek Diversion Outlet Pipe Protruding on the Dam at Lake 17 Existing Conditions Prompting Concern
Purpose and Need Statement � To enhance and utilize Lake 17 Reservoir for the benefit of the Fort Belknap Community.
2017 Watershed & Flood Prevention Operation Proposal Guidance 2014 Clean Water Act 404 Application 2014 Bureau of Indian Affairs Historic Preservation Office Findings & Report Previous 2013 Operation & Maintenance Agreements Investigations, 2012 NRCS Lake 17 Dam Plan and Little Suction Creek Diversion Drawing Reports, & 2012 Breach Summary Report Surveys 2010 NRCS Biological Assessment 1987 Downstream Hazard Assessments by Bureau of Reclamation 1967 Water Resources Survey 1965 Geology and Hydrology Survey by the BIA
TWO YEAR MINIMUM SUSTAINABILITY Year 1 Cylcle Days Utilization ET Loss Net Loss/Gain NET VOLUME 0 18.1 83.3 32.6 -32.6 0 18.1 83.3 32.6 -32.6 0 18.1 104.2 11.7 -11.7 15 62.5 114.6 -43.0 43.0 46 325.7 135.4 -327.2 327.2 76 683.8 145.8 -695.6 2164.5 107 654.7 166.7 -687.4 2898.5 2-Year 138 314.7 208.3 -389.0 2600.1 168 62.5 187.5 -116.0 2327.1 183 42.3 187.5 -95.8 2306.9 Minimum 0 18.1 145.8 -29.9 2241.1 El. = 3018.0 0 18.1 104.2 11.7 2199.4 Sustained Flow Year 2 Cylcle Days Utilization ET Loss Net Loss/Gain NET VOLUME 0 18.1 83.3 166.6 2032.8 0 18.1 83.3 166.6 2032.8 0 18.1 104.2 145.7 2053.7 15 62.5 114.6 91.0 2108.4 46 325.7 135.4 -193.2 2392.5 76 683.8 145.8 -561.6 4229.9 107 654.7 166.7 -553.4 4591.4 138 314.7 208.3 -255.0 4293.0 168 62.5 187.5 18.0 4020.0 183 42.3 187.5 38.2 3999.8 0 0.0 145.8 122.2 3915.8 El. = 3020.3 0 0.0 104.2 163.8 3874.2
Alternative #1: No Action Preliminary – Dam will breach. Downstream channel will headcut the Alternatives reservoir and so it reverts back into a prairie pothole. Existing diversion breach will widen until the natural character of an intermittent stream channel is restored. Alternative #3: Rehabilitate Dam & Decommission Diversion – Dam rehabilitation following NRCS plans. Diversion decommissioned and footprint restored to a natural intermittent stream channel.
Alternative #4: Preliminary Rehabilitate Dam & Diversion – Alternatives Dam rehabilitation following NRCS plans. Diversion rehabilitation following NRCS plans. Alternative #2 : Initially Considered But Determined ELIMINATED Not to Meet the Project Purpose: Decommission Dam & Diversion – Dam decommissioned and footprint restored to a natural prairie pothole. Diversion decommissioned and footprint restored to a natural intermittent stream channel.
Total Construction Cost = $0 Annual O&M Cost = $0 Annual Net Economic Benefit for Irrigation Based on DNRC $30 per Acre-Foot = $0 Annual Net Economic Benefit for Stock Water Based on $1 Alternative #1 Gain per Calf = $650 – No Action Lake 17 Storage Volume = 351 Acre-Feet Potential Water Available for Irrigation Based on 19.99” of Water Required for Alfalfa = 0 Acres Potential Water Available for Livestock Based on NRCS 25 gallons per Day for Cow-Calf Pairs = 12,534 Cow-Calf Pairs *Max Cow-Calf Pairs for Grazing Acreage = 650
Wildlife Habitat Rated Overall Poor to Fair - Vegetated Wetland Habitat = 123 Acres - Open Water Habitat = 54 Acres - Shoreline Distance = 4.3 Miles - Potential to adversely affect 817 ac of habitat for 10 species of concern Alternative #1 – No Action Recreation Potential Rated Poor - Migratory Species Critical Habitat (Bird Watching) = Poor - Wildlife Corridors (Hunting) = Poor - Maximum Ponding Depth (Fishing) = 3.5 Feet
ELIMINATED Total Construction Cost = $340,817 Annual O&M Cost = $0 Alternative #2 : Annual Net Economic Benefit for Irrigation Based on DNRC $30 per Acre-Foot = $0 Initially Annual Net Economic Benefit for Stock Water Based on $1 Considered But Gain per Calf = $650 Determined Not Lake 17 Storage Volume = 351 Acre-Feet to Meet the Potential Water Available for Irrigation Based on 19.99” of Water Required for Alfalfa = 0 Acres Project Purpose: Potential Water Available for Livestock Based on NRCS 25 gallons per Day for Cow-Calf Pairs = 12,534 Cow-Calf Pairs Decommission *Max Cow-Calf Pairs for Grazing Acreage = 650 Dam & Diversion
Alternative That Wildlife Habitat Rated Overall Poor to Fair Was Initially - Vegetated Wetland Habitat = 123 Acres Considered But - Open Water Habitat = 54 Acres - Shoreline Distance = 4.3 Miles Determined Not - Potential to adversely affect 817 ac of habitat for 10 species of concern Recreation Potential Rated Poor to Meet the - Migratory Species Critical Habitat (Bird Watching) = Poor - Wildlife Corridors (Hunting) = Poor Project Purpose: - Maximum Ponding Depth (Fishing) = 3.5 Feet Decommission Dam & Diversion
Total Construction Cost = $1,238,281 Annual O&M Cost = $13,373 (1% of Dam Construction Cost + $15.00 O&M Costs per Acre of Irrigation) Annual Net Economic Benefit for Irrigation Based on DNRC $30 per Acre-Foot = $4,424 Annual Net Economic Benefit for Stock Water Based on $1 Alternative #3 – Gain per Calf = $650 Rehabilitate Dam & Decommission Lake 17 Storage Volume = 934 Acre-Feet Potential Water Available for Irrigation Based on 19.99” of Diversion Water Required for Alfalfa = 147 Acres Potential Water Available for Livestock Based on NRCS 25 gallons per Day for Cow-Calf Pairs = 33,353 Cow-Calf Pairs *Max Cow-Calf Pairs for Grazing Acreage = 650
Wildlife Habitat Rated Overall Fair to Good - Vegetated Wetland Habitat = 72 Acres - Open Water Habitat = 279 Acres - Shoreline Distance = 9.1 Miles - Potential to adversely affect 643 ac of habitat for 10 Alternative #3 – species of concern Rehabilitate Dam & Decommission Recreation Potential Rated Fair to Good - Migratory Species Critical Habitat (Bird Watching) = Fair Diversion - Wildlife Corridors (Hunting) = Fair - Maximum Ponding Depth (Fishing) = 6.0 Feet
Total Construction Cost = $1,998,176 Annual O&M Cost = $29,071 (1% of Dam & Diversion Construction Costs + $15.00 O&M Costs per Acre of Irrigation) Annual Net Economic Benefit for Irrigation Based on DNRC $30 per Acre-Foot = $60,570 Alternative #4 – Annual Net Economic Benefit for Stock Water Based on $1 Gain per Calf = $650 Rehabilitate Dam & Diversion Lake 17 Storage Volume = 4,038 Acre-Feet Potential Water Available for Irrigation Based on 19.99” of Water Required for Alfalfa = 606 Acres *457 Acres can be Sustained, but Agricultural Means & Methods Could Improve Potential Potential Water Available for Livestock Based on NRCS 25 gallons per Day for Cow-Calf Pairs = 72,098 Cow-Calf Pairs *Max Cow-Calf Pairs for Grazing Acreage = 650
Wildlife Habitat Rated Overall Good - Vegetated Wetland Habitat = 254 Acres - Open Water Habitat = 740 Acres - Shoreline Distance = 20 Miles Alternative #4 – Rehabilitate Recreation Potential Rated Good Dam & Diversion - Migratory Species Critical Habitat (Bird Watching) = Good - Wildlife Corridors (Hunting) = Good - Maximum Ponding Depth (Fishing) = 12.0 Feet
Wetland Determination (CWA 404 jurisdictional determination & 401 EPA regulations) THPO Consultation T&E species Environmental Economics/Socioeconomics/Income Investigations Recreation uses (Improve and conserve public recreations Required and public fish & wildlife) Land Access Permissions & Land Ownership for Improvements Irrigation Uses, Water rights, applicability to Water Compact, and agricultural water management Cumulative Impacts
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