LITTLE SHADES CREEK RESTORATION PROJECT CWA Section 319(h) Nonpoint Source Implementation Grant Project Workplan #17 ADEM Contract #C

Transcription

1 LITTLE SHADES CREEK RESTORATION PROJECT CWA Section 319(h) Nonpoint Source Implementation Grant Project Workplan #17 ADEM Contract #C

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3 PARTNERS Alabama Department of Environmental Management Cawaco Resource Conservation & Development Council, Inc. Cahaba Clean Water Partnership Goodwyn Mills & Cawood, Inc. Jennings Environmental North State Environmental Alabama Cooperative Extension System North Carolina State Cooperative Extension System Alabama Department of Transportation City of Vestavia The Nature Conservancy Ashley Woods Homeowners Association Morgan Properties

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5 LITTLE SHADES CREEK RESTORATION PROJECT CWA Section 319(h) Nonpoint Source Implementation Grant Project Workplan #17 ADEM Contract #C Beginning Date: September 2, 2009 Ending Date: September 2, 2010 Discussion of Problem and Background: Little Shades Creek is a sub-watershed of the Shades Creek Watershed (HUC ) within the Cahaba River Basin. This project is located within the City of Vestavia, Jefferson County, Alabama. The Little Shades Creek Watershed has an area of almost eight square miles and is over 35% developed. Increased development and impervious surfaces has increased the volume and velocity of stormwater entering Little Shades Creek. This stormwater has created severe erosion near the Ashley Woods Subdivision. This increased erosion makes a significant stormwater contribution to the Cahaba River which is identified on the States 303(d) list as being impaired due to sediment. The Final Total Maximum Daily Load (TMDL) for the Cahaba River Watershed (ADEM, 2005) states that, major streambank instabilities were observed at... sites on Little Shades Creek... All of the unstable sites are in the vicinity of highly urbanized areas with high percentages of impervious land cover in the form of roads, parking lots, and roofs. Magnified peak runoff from these urban areas has caused irreversible changes in stream channel structure that will continue to evolve and discharge sediment. Goal: Implement components of the Final Total Maximum Daily Loads (TMDLs) for the Cahaba River Watershed (ADEM, 2005) by reducing contributions of sediment from Little Shades Creek to the Cahaba River. Objectives: 1. Control acceleration of erosion and reduce sedimentation by utilizing natural channel design techniques. 2. Install appropriate BMPs to remediate runoff from urban sources. 3. Provide education regarding nonpoint source pollution and effective stormwater management techniques. Methods: Natural stream channel design techniques will be implemented to improve stream and floodplain functions. Restoration efforts are expected to: Provide a stable stream channel that efficiently transports water and sediment delivered by the watershed while maintaining its dimension, pattern, and profile - neither degrading nor aggrading. Improve the water quality and aquatic habitat of the stream. Improve the floodplain functions of water storage and habitat. Reduce stormwater quality and quantity impacts to the stream by installing innovative stormwater best management practices. Help educate citizens about water quality protection, nonpoint source pollution, and natural stream channel design and restoration, using workshops and signage along the steam corridor. Deliverables and Outputs: 1. Restore approximately 1,900+/- feet of stream channel using natural channel design. 2. Enhancement of an existing constructed wetland. 3. A workshop to promote the use of natural channel design techniques as a management tool for improving water quality and aquatic habitat. 4. A workshop to promote the use of innovative stormwater runoff water quality and quantity best management practices. 5. Development of a watershed-based management plan for Little Shades Creek that incorporates applicable EPAs a-i Section 319 grant guideline components for an effective watershed management plan.

6 1. Restore approximately 1,900+/- feet of stream channel using natural channel design The Little Shades Creek Enhancement project in Vestavia Hills, Alabama, is funded by a Clean Water Act Section 319 grant administered by USEPA, ADEM, and the Cawaco RC&D Council. The goals are to improve water quality, habitat, and stream stability in 1,500 linear feet of Little Shades Creek and provide a demonstration of urban natural channel design stream enhancement and stormwater management. Little Shades Creek is a sub-watershed of the Shades Creek Watershed (HUC ) within the Cahaba River Basin. The project is located in the in the Ashley Woods subdivision in the City of Vestavia Hills in Jefferson County, Alabama. The watershed at the project site has a drainage area of almost eight square miles and is over 35% developed. The existing conditions of the stream reach were found to be impaired due to severe streambank erosion, mid-channel sediment bars in areas of overwide channel bottom, lack of deep-rooted native riparian vegetation on some streambanks, non-native invasive plants, lack of in-stream habitats, and stormwater discharges from adjacent parking lots and streets. The stream bed material consists of gravel/cobble overlaying bedrock. Project constraints include sewer lines crossing under the streambed, a greenway trail along the left bank, bridges upstream and downstream, and several stormwater outflow pipes and channels. Figure 1 shows typical existing conditions. Figure 1 Photos of existing conditions before enhancement (September 2009) The enhancement project initiated in January, 2010, includes the following elements: Channel realignment to provide a naturally stable meander pattern reducing stress on tight bends; Channel re-shaping to create a stable bankfull channel, floodplain benches on both sides, and stable terrace slopes on both sides; Installation of 11 in-stream boulder and log vane structures to direct flow away from streambanks, improve bedload sediment transport, provide grade control, and improve fish habitat; Streambank stabilization with native grass seeding, straw, temporary matting, and a brush mattress to reduce streambank erosion while permanent vegetation becomes established; Re-grading and stabilization of 10 stormwater outfall channels to minimize impacts of stormwater runoff from both sides of the stream project; Planting of native riparian trees, shrubs, and wetland plants to provide permanent streambank stability, shade and food for aquatic habitat improvements, and improved aesthetics.

7 Implementation began January 26, 2010, with mobilization and establishment of the staging area. Construction was completed March 5, with planting completed March 12, Project construction proceeded in 200-ft segments from downstream to upstream. After each segment was completed, exposed streambanks were stabilized with straw and coir erosion control matting to prevent potential erosion during rainfall events. Each project element is described below. Channel realignment consisted of excavating a new channel thalweg and low-flow channel following a sinuous path of repeating meanders down through the valley. Meander bends were created with low radius of curvature (approximately 70 to 90 ft) to minimize near-bank stress on the outside meanders during high flows. Channel re-shaping consisted of creating stable channel cross-sections for riffles, runs, pools, and glides with bankfull benches at 2.0 ft above low-flow water surface. This configuration provides for effective sediment transport and reduced shear stress during abovebankfull flows. Figure 2 shows the realigned and re-shaped channel during low flow and bankfull flow conditions (March 10, 2010). Figure 2 Realigned and re-shaped channel during low flow and bankfull flow conditions This project includes 7 boulder vanes and 4 log vanes structures to direct flow away from streambanks, improve bedload sediment transport, provide grade control, and improve fish habitat. The vanes are located on the outside banks of meander bends and are keyed into the bankfull benches to prevent scouring around the ends. Each constructed meander bend has two vanes in series to maximize bank protection. All but one of the boulder vanes include j-hooks to provide grade control, promote scour pools for habitat, and enhance sediment transport through the middle of the channel. The most downstream boulder vane is a short vane without a j-hook positioned to protect the left bank bench created from fill material. The most upstream log vane includes a boulder j-hook similar to the boulder vanes. The other log vanes do not include j-hooks and are positioned to protect bank stability during high flows.

8 Typical boulder vane lengths are ft with 4-5% arm slopes and offset angles of approximately 25 degrees from the streambank. The log vanes are shorter (30-40 ft) with lower slopes (2-4%). The vane arm boulders are sealed by chinking small rocks into gaps and placing a woven filter cloth upstream of the boulders. The upstream area between the boulders and stream bank is backfilled with cobbles and gravels to prevent flow from passing under or between the boulders. The vane arms are anchored into the streambank with sill boulders buried 5-10 feet into the bank to prevent cutting around the structure during high flows. For log vanes, there are 2-3 logs buried behind and below the header log for stability. The log vane arms are sealed by nailing a woven filter cloth to the upstream side of the vane arm log and draping it over the backer log. The upstream area between the logs and stream bank is backfilled with cobbles and gravels to prevent flow from passing under or between the logs. The vane arms are anchored into the streambank with 10-ft long root wads placed perpendicular to the stream bank just downstream of the log vane root wad to prevent cutting around the structure during high flows. Under the top log is a ledge on the downstream side to provide fish cover. Figures 3 and 4 show boulder and log vanes, respectively. Figure 3 Photos of boulder j-hook vanes under construction and during high flow directing flow away from streambank Figure 4 Photos of log vanes showing typical slope and angle and submersion in low flow to prevent rapid decomposition

9 Streambank stabilization consisted of seeding with a riparian grass mix, applying straw for temporary erosion control, applying temporary biodegradeable coir matting, and installing a brush mattress in an area of high stress for added bank protection. Figure 5 shows the brush mattress installation. Figure 5 Photos of brush mattress installation using live cuttings of dormant silky willow and silky dogwood anchored in soil and covered with straw and chicken wire to proect the cuttings until root establishment in spring and summer The 10 stormwater outfalls on both sides of the stream ranged from short, steep channels to long, flat conveyances. The steep channels were lined with boulder steps to prevent erosion. The flat channels were converted to bio-swales by lining the bottom with sandy soil and coir matting. These were planted with wetland plants to promote retention, infiltration, and filtering of stormwater runoff. Some of the bio-swales have step-pools at the ends to drop water down into the stream. Figure 6 shows typical stormwater outfalls. Figure 6 Photos of stormwater outfalls including a flat bio-swale with a step-pool drop structure at the end and a steep cascading boulder lined channel

10 Riparian planting included native trees, shrubs, and wetland plants to provide permanent streambank stability, shade and food for aquatic habitat improvements, and improved aesthetics. Plants were installed in zones depending on wetness as shown in Figure 7. Figure 7 Photos of vegetation including wetland plugs, bare-root seedlings, and container shrubs and trees 2. Enhancement of an existing constructed wetland The City of Vestavia is currently working with Goodwyn Mills and Cawood, Inc. to design, repair and expand existing wetland. 3. A workshop to promote the use of natural channel design techniques as a management tool for improving water quality and aquatic habitat 4. A workshop to promote the use of innovative stormwater runoff water quality and quantity best management practices Two workshops were held in conjunction with the Little Shade Creek Stream Restoration project, Stream Restoration Construction on February11, 2010 and Vegetation for Stream and Floodplain Restoration on March9, These hands-on workshops offered natural resource professionals and local stakeholders an opportunity to learn more about stream enhancement and restoration on an urban stream. Continuing Education Units from Auburn University were offered for each training. The field activities for the Restoration Construction workshop included channel and floodplain grading; in-stream boulder and log structure placement for flow direction, grade control, and habitat enhancement; Stream bank stabilization using root wads, erosion control matting, and vegetation; Stormwater treatment and conveyance using bio-swales and bio-retention. 25 participants met at the field site for lectures and demonstrations by stream restoration design and construction professionals (Alabama Cooperative Extension System, North Carolina State Cooperative Extension System and North State Environmental.) The workshop participants included representatives from local and state government, non-profit organizations, local business, and private industry.

11 Figure 8 Photos from the Construction Workshop

12 30 participants were part of the Vegetation for Stream and Floodplain Restoration workshop. The field activities for this workshop included:,riparian tree and shrub selection and planting; Bioengineering for stream bank stabilization; and Invasive plant management for Streamside Forests. The workshop participants included representatives from localand state government, nonprofit organizations, local business, and private industry. Evaluations from workshop participants were positive. Figure 9 Photos from the Vegetation Workshop

13 5. Development of a watershed-based management plan for Little Shades Creek that incorporates applicable EPAs a-i Section 319 grant guideline components for an effective watershed management plan. A draft of the watershed management plan was submitted to the Alabama Department of Environmental Management October, A final draft is currently being completed. 6. Other March 8-15, 2009 Immediately after construction, a large rain event tested the site. The area received an average rainfall between 6-8 inches. No major erosion or maintenance issues were discovered. Figure 10 National Weather Service Rainfall Totals March 8-15, 2010