Quantifying the Benefits of Stream Restoration

Transcription

1 Quantifying the Benefits of Stream Restoration 10 th Annual GAFM Technical Conference, March 2016 Jarrod Karl, Hazen and Sawyer

2 Presentation Outline Benefits of Stream Restoration The Watershed Approach Regulatory Drivers for Stream Restoration Case Studies Rockville, MD Quantifying Benefits Charlotte, NC Out-of-Kind Mitigation Credits

3 Restoration Manipulation of the physical, chemical and/or biological characteristics of a site with the goal of returning natural or historic functions to a former or degraded aquatic resource.

4 Rosgen Restoration Priority Options

5 Why Restore Streams? Improve water quality Improve wildlife habitat/fisheries Stabilize streambanks to protect infrastructure Slow and store flood waters Mitigate for adverse impacts to Waters of the U.S.

6 Benefits of Stream Restoration Channel Improvements Prevented sediment during storm flow Nutrient processing at base flow Reconnection of stream and floodplain Improved instream and riparian habitat Glenora Tributary, Rockville, MD

7 Benefits of Stream Restoration Floodplain Improvements Floodplain processing of sediment and nutrients Increased floodplain access and storage Improved terrestrial and wetland habitat Educational and recreational opportunities (e.g., greenways)

8 Limitations of Stream Restoration Changes in watershed hydrology due to urbanization reduces effectiveness of stream only projects Functional improvement is limited in developed areas without other prevention and restoration measures

9 The Watershed Approach New ordinances help protect streams and water quality Existing impervious requires retrofits Developed watersheds will never recover without upland control measures and stream corridor restoration Regulatory sticks and carrots

10 Regulatory Requirements Quantifying the Benefits of Stream Restoration to the Chesapeake Bay

11 Chesapeake Bay TMDL Pollution diet for the bay Established December 29, 2010 Annual Limits 185.9M lbs of N (-25%) 12.9M lbs of P (-24%) 6.45B lbs of sediment (-20%) Fully Implemented by % Implemented by 2017 Stream restoration included as a way to earn load reduction credits

12 CBP Expert Panel Recommendations

13 CBP Expert Panel Recommendations Quantifies removal rates and credits for stream restoration projects Four protocols that may apply Prevented Sediment Nutrient Processing Floodplain Reconnection Regenerative Stormwater Conveyance

14 Protocol 1 Credit for Prevented Sediment During Storm Flow Pollutants of concern are sediment, TN & TP Method Calculate sediment loads using Rosgen s BANCS method (BEHI/NBS) Convert sediment load to nutrient load 1.05 lbs P/tn sediment 2.28 lbs N/tn sediment Estimate stream restoration efficiency (usually 50%)

15 Protocol 2 Credit for Instream and Riparian Nutrient Processing During Base Flow Pollutant of concern is TN Method Determine post-construction stream length that has been reconnected using BHR of 1.0 or less Determine dimensions of hyporheic box for each reach Multiply the hyporheic box mass by the unit denitrification rate (1.06 x 10-4 lbs/ton/day of sediment) Compute annual denitrification rate for the watershed

16 Protocol 3 Credit for Floodplain Reconnection Volume Pollutants of concern are sediment, TN & TP Method Estimate the floodplain connection volume in the floodplain area through detailed pre/post H&H modeling Use curves to estimate the N and P removal rate attributable to floodplain reconnection for the floodplain reconnection volume achieved Compute the annual T, P and TSS load delivered to the project Multiply the pollutant load by the project removal rate to define the reduction credit

17 Protocol 4 Credit for Dry Channel Regenerative Stormwater Conveyance (RSC) as an Upland Stormwater Retrofit Pollutants of concern are sediment, TN & TP Method Determine stormwater treatment volume Define removal rates using adjustor curves from retrofit guidance document

18 Case Study Upper Watts Branch, Rockville, MD Streams run through forest preserve Existing stormwater control measures in watershed do not adequately control channel protection volume Streams are in a state of disequilibrium Restoration is needed to correct morphology and stabilize the watershed

19 Case Study Upper Watts Branch, Rockville, MD Stream Restoration Tributary 1 Tributary 2 Main Stem Outfall Stabilization Outfall 1 Outfall 2 Outfall 3

20 Case Study Protocol 1 Upper Watts Branch, Rockville, MD

21 Case Study Protocol 1 Upper Watts Branch, Rockville, MD

22 Case Study Protocol 2 Upper Watts Branch, Rockville, MD

23 Case Study Protocol 2 Upper Watts Branch, Rockville, MD

24 Case Study Protocol 2 Upper Watts Branch, Rockville, MD Total for Protocols 1 & 2 N = 2,119 lbs/yr P = 1.7 lbs/yr Sediment = 3,224.7 lbs/yr

25 Regulatory Incentives Out-of-Kind Mitigation for Functional Improvement in Developed Areas

26 Compensatory Mitigation Permits required for impacts to Waters of the United States Section 10 Section 404 Mitigation required for significant adverse impacts to WOUS In-kind (preferred) Out-of-kind (case-bycase)

27 Edwards Branch Credits based on length of stream influenced by SCM How much influence? Credits earned by SCM Condition ( Stream Condition ( Good/Fair Bugs; or Water Quality Improvement

28 Edwards Branch Overall WQ improvement based on TSS reduction, since sediment is a major cause of impairment in the watershed Success based on meeting the TSS criterion of 600 lbs/acre/year or all of the SCMs meeting performance expectations

29 A New Charlotte Method Way to relate SCM performance to stream functional improvement Based on sediment relationship between SCMs and streams Borrows from Edwards Branch s focus on annual watershed TSS load as an indicator of watershed health TSS used as a surrogate for H&H benefits and total pollutant reduction Considers each SCM s performance, position in the watershed and influence on receiving waters Simple, easily calculated, and easily understood

30 A New Charlotte Method 1. Determine annual TSS load reduction for each SCM in lbs/yr using Simple Method. L P P R C A Where: L Annual mass of pollutant export lbs/yr P Annual precipitation in/yr P Correction factor for storms not producing runoff R Runoff coefficient C Average concentration of pollutant mg/l A Drainage area acres

31 A New Charlotte Method 2. Determine the unit annual stream bank erosion rate reduction (lbs/lf/yr) of the proposed stream restoration using the BANCS model. Improvement between existing and proposed. Assumes moderate to very low erosion for restored stream. Using proposed stream restoration encourages headwater SCMs

32 A New Charlotte Method 3. Express the benefit of the SCM in units of stream length (lf) using the following equation: Positive SCM Impacts Annual TSS Load Reduction of SCM / Unit Annual Stream Bank Erosion Rate / / Condition: SMUs generated by SCMs cannot exceed the number of SMUs generated by stream improvements.

33 Case Study Monteith Park

34 Case Study Monteith Park Credit Type Size Total Credits Stream Restoration 3,297 3,297 Stream Enhancement Stormwater 5 SCMs 3,474 6,948

35 Case Study Monteith Park Five Bioretention SCMs installed at existing outfalls Total treatable drainage area of 18.9 acres Annual TSS load reduction of 8303 lbs/yr Unit annual erosion rate reduction of lbs/lf/yr for Monteith Creek Stream mitigation credit equivalent of 3,876 SMUs

36 Maintenance Partnership Short-term maintenance (5 years) of stream and SCMs provided by mitigation provider Long-term maintenance provided by Town of Huntersville Provide annual load reductions to waters in their jurisdiction Local relationship with the neighborhood HOA

37 Summary Stream restoration provides numerous benefits Developed areas benefit from a combination of stream restoration and upland stormwater controls Regulatory sticks and carrots are both needed for watershed recovery in developed areas Stream restoration can be used to help meet regulatory sticks such as the Chesapeake Bay TMDL Alternative/out-of-kind mitigation scenarios can provide a carrot for integrating stormwater controls and stream restoration

38 Thank You Charlotte Mecklenburg Storm Water Services Water and Land Solutions Georgia Association of Floodplain Management