Black Gore Creek Sediment Source Monitoring and TMDL Sediment Budget

Transcription

1 Black Gore Creek 2012 Sediment Source Monitoring and TMDL Sediment Budget Prepared for: The Eagle River Watershed Council Prepared By: RiverRestoration.org -

2 I. Introduction Interstate 70 is a major highway corridor for east-west transportation in Colorado. The highway is located in central Colorado with high mountain passes that cut through the Rocky Mountains. The study area is where Interstate-70 travels over Vail Pass in the Black Gore Creek Watershed. The Colorado Department of Transportation has an easement agreement with the United States Department of Agriculture, White River National Forest, to operate and maintain I-70 through the Black Gore Creek Watershed. Vail Pass experiences heavy snowstorms, high winds, and near whiteout conditions throughout the winter. These storm events are common starting in October and persisting until May every year. The Colorado Department of Transportation requires careful operations and maintenance to keep the highway safe and open. In order to keep Vail Pass open during these snow events, CDOT applies traction sand and deicers to the highway. An alternative is to temporarily close the highway when snow events are too extreme. On an average year, CDOT applies over 15,000 tons of traction sand to the highway corridor. It is estimated that over 180,000 tons of sediments have accumulated and are stored within the watershed (SCAP, 2005). The United States Department of Agriculture requires watershed health to be in Proper Functioning Condition as defined in the Forest Service Manual. The watershed condition policy requires implementation practices to maintain or improve watershed condition to sustain ecosystems, water quality and other attributes related to watershed processes. Black Gore Creek runs from the top of Vail Pass at 10,617 feet to the confluence with Gore Creek at 8,680 feet. Black Gore Creek was put on the 303(d) impaired wasters list by the State of Colorado in The designation was based on excess sediments in the channel impairing aquatic life beneficial uses. Sediments have filled pools, smothered gravels and cobbles, exacerbated bank erosion, and diminished aquatic habitats. A Total Maximum Daily Load was developed to define stream health indicators and targets for meeting aquatic life designated uses. As part of the adaptive management plan developed in the TMDL, annual sediment source monitoring is conducted. This report presents results from the 2012 monitoring efforts. The purpose of the study is to evaluate sediment sources in the watershed and quantify the load allocation from these sources to develop a sediment budget. The sediment budget presented herein quantifies a recommended sediment load for export during the summer-fall maintenance operations for In addition, areas are identified to assist with prioritizing projects for watershed restoration and best management practices to reduce sediment loading. The Total Maximum Daily Load was developed in collaboration with the Colorado Department of Transportation, the United States Department of Agriculture, the Eagle River Watershed Council, the Eagle River Water and Sanitation District, the Town of Vail, Eagle County, Colorado Department of Public Environmental Health, RiverRestoration.org, and interested citizens. The TMDL takes an adaptive management approach to evaluate watershed health and implement projects. Each year these partners develop and implement strategies to restore stream health and remove Page 1-29-

3 Black Gore Creek from the 303(d) impaired waters list. The long-term goal is to meet State designated aquatic life uses; as well as the USDA requirement to maintain robust health in national forest lands. II. Methods During a cold snap but clear break from snowstorms, RiverRestoration.org conducted the Sediment Source survey efforts on October 6th-8 th, Construction crews from the Colorado Department of Transportation were actively repairing two culverts near mile marker Heavy equipment traction marks indicated that sand removal from the shoulders and basins had recently occurred. Eight sediment source categories were monitored, these include: Erosion Control Basins (ECB); Fill Slope Gullies (FSG); Valley Floors (VF); Photo Monitoring (PM); Bridge accumulation (BR); Center Median (CM); Cut Slopes (CS); and Fill Slopes (FS). The longitudinal profile monitoring at MM186.5 was not conducted because thick ice prevented wading the channel. A detailed description of sediment source monitoring procedures is in the BGC Sediment Source Monitoring Field Guide (Total Maximum Daily Load, 2007). The mileage stationing used to identify reference points and locations were based on aerial photographs (digitized in 2006), as well as CDOT benchmarks and Interstate-70 mile markers along the highway. Reference points may vary +/-0.1 mile. III. Results Cross Section Surveys Cross section surveys show changes in topography within the Black Gore Creek channel, at fill slope gullies, and erosion control basins. These cross sections are monitored to show the aggradation or degradation that occurs over time. Three inchannel locations are monitored with cross section surveys; the Black Gore Creek channel at MM 186.5, upstream of the Gore Creek confluence near the Waste Water Treatment Plant, and the in-channel catchment basin at MM (Basin of Last Resort). During the 2012 monitoring efforts two Fill Slope Gullies were monitored at MM 187.5, and MM Fill slope gullies located at MM 186.8, 185.9, and were restored in 2011 and monitored with Photographs. In-channel Catchment Basin of Last Resort MM Two cross sections have been monitored at the Basin since In the fall of 2008 sediments were excavated from the in-channel catchment basin, the project was titled Basin of Last Resort. Cross section #1 is located approximately 30 feet upstream from the boulder grade control structure. Monitoring data shows an average of 1.25' of deposition between 2009 and 2011 on the left side of the channel. There is no change between 2011 and Page 2-29-

4 Figure 1: Basin of Last Resort x-section #1 Basin of Last Resort X-Sec # Photograph MM x-sec # Page 3-29-

5 Photograph MM x-sec # After Sediment Removal Project Photograph MM x-sec # Page 4-29-

6 Cross Section #2 is located approximately 70 feet upstream of cross section #1, near the upstream 1/3 of the Basin. Significant deposition occurred between 2009 and The cross section shows that sediments are near the grade elevation pre-removal of sediment. The cross section shows there may have been scour of sediments between 2011 and The left 1/3 of the channel shows an average of 1.0 of scour, the middle shows 0.75 of scour and there is no change to the right 1/3 of channel. Figure 2: Basin of Last Resort x-section #2 Basin of Last Resort X-sec # Photograph MM x-sec # Page 5-29-

7 Photograph MM x-sec # Photograph MM x-sec # Page 6-29-

8 Beaver Activity Reach MM This reach is characterized by extensive beaver activity in a moderate gradient channel with low sinuosity meandering plan form and gravel substrate. Cross section and longitudinal surveys of the channel at MM show local deposition and scour, and lateral migration changes in the channel from beaver dam activity. Surveys show the channel can change up to 1.5' in bed elevation within a year and the channel may be migrating to the right. The beavers construct their dams at the relatively the same location every year. Cross sections #1 is located approximately 50 feet upstream of a beaver dam. Sand and fine sediment are deposited on native gravels. In 2008 the beaver dam was not active. This reach shows about 0.5 feet of deposition depending on beaver activity. Figure 3: MM186.5 Beaver Activity Reach x-sec #1 MM Beaver Activity Reach X-Sec # Cross section #2 is located 6 feet upstream of a beaver dam. Thick ice had formed in 2012 and the survey was unable to pick up data within the channel. Figure 4: MM Beaver Activity Reach x-sec #2 MM Beaver Activity Reach X-sec # Page 7-29-

9 Cross Section #3 is located approximately 125 feet downstream of a beaver dam and 110 upstream of a beaver dam. Both of the beaver dams were active in The cross section shows an average of 0.5 of sediments transport through the section depending on the construction of the downstream beaver dam. The cross section shows a side channel is forming on river right. Figure 5: MM Beaver Activity Reach x-sec #3 MM Beaver Activity Reach X-sec # Channel Survey Upstream Confluence at Waste Water Treatment Plant (WWTP) Cross section #1 is located upstream of the confluence with Gore Creek. The cross section shows degradation of the main channel and cutting of a side channel between 2004 and No changes have occurred between 2008 and Figure 6: WWTP x-sec #1 WWTP X-Sec #1 Elevation Station Page 8-29-

10 Cross section #2 is located near the Waste Water Treatment Plant building. The cross section survey shows degradation of the main channel between 2004 and The survey and field observations show sediment deposition to the floodplain bench. Over the past few years no morphological changes to the channel have been surveyed, however field observations have noted significant algal growth over in this step gradient reach. Figure 7: WWTP x-sec #2 WWTP X-Sec # Photograph of algae growth in main channel Page 9-29-

11 Valley Floor Gully at MM There are two storm water pipes that discharge onto the valley floor at The west pipe is clogged with sediments and has been inactive since monitoring commerced in The east pipe drains the WB shoulder. The narrow shoulder limits the capacity of erosion control basins; there are two small subsurface basins up gradient of the storm water pipe inlet at the WB shoulder. These basins are often full during the monitoring efforts. Delta deposits and the gully formed at the outlet of the active storm pipe was stabilized in Crib structures were built at cross section #2 to stabilize the delta. Cross logs (check dams) were constructed at cross section #1 for grade control of the gully. Additional crib structures were constructed at the floodplain bench to retain sediments that were excavated out of the channel. Cross section #1 shows gully degradation. Two cross logs were not keyed subgrade deep enough to provide grade control. The cross section shows sediments are transporting through the gully with local scour and deposition. Figure 8: VF x-sec #1 Gully Stabilization Project VF MM187.5 X-sec # PreProject 2006-PostProject Cross section #2 shows the gully channel is filling with sediments. Downstream of the cross section the grade control structures are head-cutting. Figure 9: VF x-sec #2 Gully Stabilization Project VF MM187.5 x-sec # PreProject 2006-Post Project Page

12 Photograph showing deposit in BGC channel at MM The left photograph shows the head-cutting of the grade control structures. The right photograph is looking down gradient at x-sec #2 showing sediment deposition. Page

13 Fill Slope Gullies The Colorado Department of Transportation repaired failing culverts down the fill slopes at MM 186.8, MM and MM Cross section surveys were not conducted at these repaired gullies because construction crews were actively restoring the slopes. A new monitoring station was established on the fill slope at MM Two cross sections were surveyed to monitor the failure of the culvert on the fill slope. This station was selected because the outlet of the pipe is head-cutting at the toe of the fill slope and the surface of the slope appears to be slumping. Photographs shows before repair project 2010 at Fill Slope Gully MM Photographs shows after repair project 2012 at Fill Slope Gully MM Page

14 Photograph shows before repair project in 2010 at FSG MM Photograph shows after repair project in 2012 at FSG MM Page

15 Photographs are looking down slope before repair project 2010 at FSG MM Photograph is looking down slope after repair project 2012 at FSG MM Page

16 Fill Slope Surveys Fill Slope surveys are monitored by visual observation of the sedimentation of the fill slope, vegetation cover, and rilling at the top of the slope. Heavy rilling with smothered vegetation cover indicates uncontrolled storm water that transports sediments down the fill slopes. Table 1. Fill Slope Surveys Location Notes # Rills per 25 / % veg cover # Rills /% veg cover # Rills/ % veg cover FS WB FS WB FS WB FS WB FS WB FS EB FS EB FS EB 0/80 0/80 0/80 0/80 0/80 0/80 2/70 0/70 0/70 Heavy sedimentation down fill slope. Beaver dam reach and aggraded channel. New paved shoulder and swale effective at routing sediments, however basin is small and not adequate capacity. 0/80-0/80 0/80-0/70 Shoulder recently graded and no rilling, however heavy sedimentation on slope. 4/80 2/80 3/75 Deposits at toe of slope. 0/70 7/75 5/75 11/70 Gully 0/75 Fill slope repaired, however heavy sidecast material at Page

17 top of slope. New curb routes storm water to bike path swale and basin at FS EB FS EB FS EB FS EB FS EB FS EB FS EB FS EB FS EB 4/ EC logs at top of slope. Repaved bike path. Sheet flow drains to swale and not down slope. 2/ EC logs at top of slope. Repaved bike path. Sheet flow drains to swale and not down slope. 3/ EC logs at top of slope. Repaved bike path. Sheet flow drains to swale and not down slope. 9/70 15/75 7/85 13/70 0 9/80 6/ EC logs installed at top of slope. 2/ EC logs installed at top of slope behind jersey barrier. 0/75 0/85 0 EB shoulder and bike path drain to large basins at /65 0/70 12/70 EC logs partially buried with sediments. Page

18 Photograph shows BMPs installed at Fill Slope MM Curb routes storm water to culvert minimizing sheet flow down fill slope. Erosion control logs minimize sediments from transporting down slope into Black Gore Creek. Photograph shows example of no BMPs installed at Fill Slope MM Page

19 Single Depth Surveys The depth of sediment is measured at reference posts at Bridges and Valley Floors. Deposits at posts are assumed to be transporting sediments through the watershed and used as an indicator in the load allocation for the TMDL budget. Table 2 Single Depth Measurement Surveys Location Notes Sediments at Post BR Yes Yes No Significant riling and accumulation under bridge. A small drainage is transporting sediments through the floodplain bench, however no significant deposition is at the reference post. BR Yes Yes Yes Sediments at post are likely from side-cast material. BR Yes Yes Yes Sediments at post are likely from side-cast material transported from drainage outfall at ECBs under bridge. VF No Yes No No sediments are at the post, however there are three delta deposits upslope of post at toe of fill slope. VF Yes No No No new sediments at post. Vegetation has established on deposits. VF Yes Yes Yes Post is buried and could not be found. The flow path meanders through the deposit; flow has shifted from toe of fill slope to center of valley floor. This post is located down gradient of FSG culvert repair project. Page

20 Photographs show the Valley Floor deposit at MM Page

21 Center Medians Center Medians are measured by a topographic survey 10, 20, and 30 upslope of the culvert invert. Depth probes of sediment are also taken at the invert and used as an indicator for the load allocation in the TMDL budget. Table 3 Center Median Surveys Location Notes Sediments at Invert CM No sediments at invert of culvert. CM Smothered vegetation. Can't find invert of culvert. CM Significant side cast. Median reconstructed. Can t find culvert invert. CM Trace Sediment deposition at invert. Erosion Control Basin Surveys Visual observations of the sedimentation at Erosion Control Basins are used to indicate the load allocation from Cut Slopes and Bike Path Swales. The 2012 clean-out efforts were conducted prior to the sediment source monitoring. Table 4 Erosion Control Basin Survey I-70 EB Sedimentation Distance to storm water control Notes Clean /23 Clean Clean - Small and not adequate capacity. Potential to expand basin upslope and pave shoulder to route sediments Full 0.4 Located east of chain station, potential to expand basin Full 0.2 Recently graded shoulder and Page

22 cleaned out basin Full 1.0 Shoulder recently cleaned and graded but basin is full. Culverts at 183.4, 183.8, Uncontrolled from Bridge at to culvert Full 0.3 Small basin with large shoulder and potential to expand Clean - Recently cleaned, however limited capacity. Trees at top of slope are dead and recently removed. Room to expand basin capacity Full 0.1 Not adequate capacity Full Full 0.2 Room to expand basin size Full 0.1 Not adequate capacity Clean - Not adequate capacity Removed? Full 0.2 Two small basins, not adequate capacity Full 0.9 Three basins with room for expansion Full 0.2 Not controlled from to Sediments upslope of Black Lakes are not counted in the load allocation for BGC. Sediments are stored in Black Lakes, unless sediments at invert are monitored indicating transport out of the lake. Page

23 I-70 WB Clean Clean - Reverse drainage to ECB at Full 0.1 Limited capacity Full 0.1 Subsurface basin Clean - Two subsurface Clean Full 0.2 Wood debris and sand fill basin. Another small basin at is small and full Clean Clean - Not adequate capacity Full 0.1 Subsurface Full 0.2 Subsurface Clean Clean - Adequate capacity, two basins Clean - Small basin. Room for expansion Full Full 0.3 Two small basins are completely buried. Recently graded, berm on shoulder help control sheet flow down fill slope. Page

24 Bike Path Swales Full 1.0 New curb routes storm water to basin. No rills or sheet flow down fill slope Full 0.3 Room to improve and expand basin Full 0.4 Large basin with adequate size Clean - *0.6 Basin is clean down slope of culvert repair project. *Uncontrolled from the spillway at Black Lakes no2 to the culvert at Photographs show example of culverts transporting sediment to the bike path swale with no control between MM Page

25 IV. Sediment Source Load Allocation and Budget Data collected from the monitoring efforts are used to calculate a load allocation from the identified sediment sources in the watershed. A detailed description of calculations used in the Load Allocation for the Sediment Budget is in the Black Gore Creek Total Maximum Daily Load report (Appendix C, Total Maximum Daily Load, 2007). Watershed sediment sources have significantly decreased since the repair of the culverts at MM 186.8, 186.9, 187.1, and These repair projects at the failed culverts monitor zero degradation at the gullies, which is reflected as a zero load allocation for the FSG watershed source category. The Fill Slopes load allocation has also decreased with the implementation of coir roll BMPs at the top of the slope, and curbs to route the sheet flow to a storm drain. The Native Slope, Channel Banks, and Center Medians did not change. The Cut Slopes and the Bike Path Swales are the two sediment source categories monitored with an increase in the load allocation for Most of the basins were full. Many of the sediment basins are small and do not have the capacity to provide adequate storage. The Center Medians show a decrease in the load allocation most likely from vegetation establishment and coir logs controlling storm water up gradient. The Valley Floors and Bridges load allocation did not change from the previous year. The total sediment load allocation from all of the identified watershed sources is 8,725 tons. The transport capacity of the Black Gore Creek channel is estimated to be 8,600 tons per year. The total exported load of sediments for the spring-fall of 2012 was 13,699 tons. The recommended sediment export load for the 2013 season is the TMDL minimum of 6,400 tons. The Colorado Department of Transportation has shifted maintenance practices from the use of traction sand to the use of chemical deicers. In 2012, only 342 tons of traction sand was applied; 166,327 gallons of liquid deicer, and 4,322 tons of solid deicer were applied. The environmental effects of chemical deicers should be evaluated in conjunction with the Black Gore Creek sediment TMDL. Salt and chemical deicers enter the watershed through storm water, side cast, snow stockpiles, and seepage. The accumulation can pose risks to trees; decreasing the health and increasing the infestation of bark beetle and disease, and stress during drought. These studies will help CDOT implement a strategic plan to avoid the overuse of all materials and balance the use of sand, salt, and chemical deicers. Understanding the cumulative affects of sand, salt, and chemical deicers to the Black Gore Creek Watershed will help develop specific stewardship to reduce the environmental impacts, as well as continue to maintain a safe winter highway. Chemical deicers may also contribute to the mobilization of trace metals from the road and soil. Some chemical deicers contain substantial amounts of organic matter and phosphorus which may reduce the oxygen in Black Gore Creek. The decrease in oxygen could lead to an increase in the growth of algae. An increase in algae growth has been observed in the Black Gore Creek channel (see example photograph on page 9 of this report). Page

26 Table 5 DRAFT Black Gore Creek Load Allocation and Sediment Budget SOURCE CATEGORY ZONES LA (Tons/Year) LA (Tons/Year) Applied Traction Sand Sand Stockpile Erosion Slope Mass Wasting Natural Background Black Lakes Channel Bed Active Storage 3 1, Fill Slope Gullies 1,2 0 0 Fill Slopes 1, Valley Floors 2 1, Cut Slopes 1 2, Accumulation Under Bridges Increased erosion of native slopes Bike path swales 1, Center Medians Increased Bank Erosion Other 1,2,3 0 0 Sediment Sources TOTAL LA 22,982 8,725 BGC Transport Capacity (TC) 8,600 8,600 BGC Assimilative Capacity (AC) 0 Exported Sediment Load 1,2,3 20,077 13,699 Recommended Exported Load for ,2,3 6,400 6,400 * The recommended exported load shall always be equal to, or greater than 6,400 tons/year ** Load allocations are estimates based on source monitoring data collected in 2012, and Page

27 assumptions in the TMDL. ***Imported and exported load estimates for 2012 reported by CDOT in December, 2012 (BGC FY 2012). ****Monitoring results for the % fine sediments from the United States Forest Service used in the Channel Bed storage was assumed to not change between 2011 and V. Best Management Practice Recommendations Best Management Practices that should be implemented annually are the installation of silt fences, and erosion control logs at the top of fill slopes and under bridges. These simple BMPs significantly reduce the loading of sediments into the channel. Modifying maintenance operations to start clean-out efforts in June, or immediately after snow melt would also significantly reduce sediment loading into the watershed. Multiple clean-out efforts throughout the summer are necessary for maintaining capacity of small Erosion Control Basins. Projects recommended for evaluation for the 2013 year are: 1. Improve storm water routing and expand sediment basins between EB shoulder and BPS. The bedrock outcrop near may be partially removed, or a run-down structure constructed, to create a basin with adequate capacity. The curbs installed in 2012 at the fill slope side of the bike path have greatly reduced sheet flow and transport of sediments down the fill slope. However, the basins do not have the capacity to detain the storm water sediments. 2. Improve storm water routing at EB shoulder and BPS between and See concept plan for ECB expansion and storm outlet improvements near (RiverRestoration.org, 2011). 3. Improve storm water routing and expand sediment basins between WB. 4. Improve storm water routing and expand sediment basins between EB. 5. Stabilize delta deposits at Valley Floor See concept plan report (RiverRestoration.org, 2011) 6. Install catchment basins at BPS between and Continue to install annual BMPs at Fill Slopes and under Bridges. Page

28 Photograph shows basin at MM In previous years this basin has been cleaned and has good capacity, however with the improved drainage it may have filled more rapidly. Photograph is looking upslope at shoulder near MM Page

29 Photograph is looking at EB shoulder and small basin near MM Photograph shows small basin near MM Page

30 Photograph is looking at basin near MM Page