Black Gore Creek 2013 Sediment Source Monitoring and TMDL Sediment Budget

Transcription

1 Black Gore Creek 2013 Sediment Source Monitoring and TMDL Sediment Budget Prepared for: Prepared By: -

2 I. Introduction The Black Gore Creek Total Maximum Daily Load (TMDL) was developed in collaboration with the Colorado Department of Transportation, the United States Department of Agriculture Forest Service-White River National Forest, 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. Each year these partners develop and implement strategies to restore stream health and remove 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. Sediment source monitoring is conducted annually as part of the implementation plan for the Black Gore Creek TMDL. Each year an inventory and assessment of the sedimentation and watershed conditions are evaluated to adaptively manage highway maintenance and restoration of the watershed. The purpose of this report is to quantify the sediment loading, and the effectiveness of BMPs and capital improvement projects at the watershed scale. The objectives of the sediment source monitoring are to: 1.) Quantify the Load Allocation and Sediment Source Budget. 2.) Develop recommendations for BMPs and watershed restoration projects. 3.) Evaluate if current practices are effective at maintaining, or restoring desired conditions for sediment to support beneficial uses. II. Adaptive Management Recommendations for ) Install and maintain temporary BMPs. -Save money in the budget for maintenance at the end of the fiscal year. -Sweep shoulders in June, or early May, to prevent transport of sediments. -Modify maintenance operations to start clean-out efforts in June, or immediately after snow melts to reduce sediment loading beyond the highway corridor. -Silt fencing under bridge to control side cast accumulation -Biodegradable rolls upslope from Center Median 181.2, 184.5, and Biodegradable rolls across Fill Slopes with significant side cast and uncontrolled sheet flow ( ), ( ), (WB ). -Conduct frequent clean-out of small basins after storm events. 2.) Repair failing culvert, gully forming at Fill Slope, and Valley Floor at ) Improve storm water routing at shoulder and BPS between and See concept plan for Erosion Control Basin expansion and storm outlet improvements near (RiverRestoration.org, 2011). 4.) Repair Fill Slope, improve drainage, and repair three gullies forming near MM Page 1-22-

3 5.) Restore storage capacity at the Basin of Last Resort. 6.) Improve storm water routing along the bike path and shoulder between New curb needs more day light drainages. The curb is buried in sediments and flow exceeds drainage capacity, causing overflow and rilling down the fill slope near ) Improve sediment basins between A series of small basins do not have adequate capacity. The bedrock outcrop near may be partially removed, with a run-down structure to create a larger basin. 8.) Improve storm water routing and improve sediment basins between WB ) Install sediment basins along BPS between and ) Improve drainage and concentrated flow from ECBs under bridge. 11.) Stabilize delta deposits at Valley Floor ) Continue monitoring the environmental affects of liquid deicers in conjunction with the Black Gore Creek sediment TMDL. -Maintenance practices have shifted from the use of traction sand to the use of chemical deicers. There was a 270% increase from 2012 to 2013 in the use of liquid deicers. III. Methods During warm weather and clear skies, RiverRestoration.org conducted the Sediment Source survey efforts between October 1st-3rd Nine sediment source categories were monitored, these include: Erosion Control Basins (ECB); Fill Slope Gullies (G); Valley Floors (VF); Photo Monitoring (PM); Bridge accumulation (BR); Center Median (CM); Cut Slopes (CS); Bike Path Swales (BPS); and Fill Slopes (). 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. IV. Summary of Monitoring Data Basin of Last Resort MM In-channel Erosion Control Basin, known as Basin of Last Resort at MM is surveyed at two locations. Cross section #1 shows approximately 4' of deposition Page 2-22-

4 occurred on the left side of the channel, and 1.65 across the channel between 2009 and Figure 1: Basin of Last Resort x-section #1 Basin of Last Resort X-Sec # Cross Section #2 is located approximately 70 feet upstream of cross section #1, near the mouth of the channel and upper 1/3 of the basin. Cross sections surveys show the basin is reaching capacity for sediment storage. Maintenance operations should foresight another large-scale clean out effort to restore storage capacity. Figure 2: Basin of Last Resort x-section #2 Basin of Last Resort X-sec # Page 3-22-

5 Photograph MM 182.8, from x-sec#2 looking upstream at mouth of channel. Photograph MM 182.8, from x-sec#2 looking downstream at in-channel Erosion Control Basin. Page 4-22-

6 Photograph MM 182.8, from left reference post looking across x-sec #2 Beaver Activity Reach at MM This reach is characterized by a Rosgen C4 classification, low gradient slope of 1.5%, meandering plan form, and gravel substrate. Resident beavers actively construct dams, typically in the same location every year. Cross section and longitudinal surveys of the channel show local deposition and scour from beaver dam activity and sediment aggradation behind the dams. Surveys show the channel can change up to 1.5' in bed elevation within a year, and lateral migration trends toward the toe of the fill slope. In 2013 there was no beaver activity within the surveyed reach, however a large beaver dam approximately 150 yards upstream had breached. Cross section surveys show up to 0.6 feet of deposition in Considering the magnitude of the breached beaver dam, it appears most sediments transported downstream of the surveyed reach. Page 5-22-

7 Figure 3: Black Gore Creek Channel at MM x-sec #1 MM Beaver Activity Reach X-Sec # Figure 4: Black Gore Creek Channel at MM x-sec #2 MM Beaver Activity Reach X-sec # Figure 5: Black Gore Creek Channel at MM x-sec #3 MM Beaver Activity Reach X-sec # Page 6-22-

8 Photograph MM 186.5, from top of fill slope looking down at beaver activity reach. Valley Floor 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 commenced in The east pipe drains the WB shoulder. The narrow WB shoulder has two small subsurface basins, which fill after storm events. A delta formed at the outlet of the pipes on the valley floor. In 2006, restoration efforts stabilized the delta deposit and the gully at the outlet of the east storm pipe. Timber structures were constructed to hold the delta deposits and to stabilize the gully channel. An additional timber structure was constructed at the floodplain bench to detain sediments that were excavated out of the Black Gore Creek Channel. Restoration of the east culvert storm pipe, fill slope, and repair of the gully structures are recommended for 2014 capital improvement projects. Cross section surveys show hill slope slumping of the fill slope and head cutting at the outlet of the pipe. Storm flow has eroded under the cross logs and de-stabilized the timber structures in the gully channel across the valley floor. Page 7-22-

9 Figure 6: VF x-sec #1 Gully Stabilization Project VF MM187.5# /pre-restoration 2006/post-restoration Figure 7: VF x-sec #2 Gully Stabilization Project VF MM 187.5# /pre-restoration 2006/post-restoration Page 8-22-

10 Photograph VF MM 187.5, looking up at gully and culvert. Photograph VF 187.5, looking down gully towards Black Gore Creek. Page 9-22-

11 Fill Slope Surveys The Colorado Department of Transportation repaired failing culverts down the fill slopes at MM 186.8, MM and MM No cross section surveys were conducted at the repaired culverts, however these were monitored with photographs. In 2012, a new cross section survey was established on the fill slope at MM Fill Slope culvert at MM is failing. Cross section surveys show slumping of the slope and head cutting at the culvert outlet. Figure 8: Fill Slope Gully MM187.5#1 Fill Slope Gully MM187.5 x-sec# Figure 9: Fill Slope Gully MM187.5#1 Fill Slope Gully MM187.5 x-sec# Page

12 Photographs looking up at Fill Slope culvert at MM Photograph looking down Fill Slope from X-section #2 Page

13 Sediment transport down the fill slopes 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 # Rills/ % veg cover WB WB WB WB WB /80 0/80 0/80 0/85 Needs weed control 0/80 0/80 0/80 0/85 Needs weed control 2/70 0/70 0/70 6/65 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 6/65 Heavy side cast accumulation 0/80-0/70 0/75 Heavy side cast accumulation. 4/80 2/80 3/75 9/70 Rilling behind EC logs. Heavy side cast accumulation. Deposits on bench and at toe of slope. 0/70 7/75 5/75 4/75 Rilling and heavy side cast. Page

14 /70 Gully 0/75 5/65 Fill slope repaired, however heavy sidecast material at top of slope. New curb routes storm water to bike path swale and basin at Curb is over loaded and needs additional drainage. Heavy rilling behind curb. 4/ /75 EC logs control sediments. 2/ /80 EC logs control sediments 3/ /75 Rilling behind EC logs. Need for repair/replace maintenance. 9/70 15/75 7/85 4/75 Rilling behind EC logs. Need for repair/replace maintenance. 13/70 0 9/80 0/80 EC logs control sediments. 6/ /80 EC logs control sediments. 2/ /55 Rilling and heavy side cast sedimentation /75 0/85 0 See Gully survey Large shoulder recommended for sediment basin and drainage improvements /65 0/70 12/70 4/70 EC logs partially buried with sediments. Page

15 Photograph looking towards and EC log in need of repair. Photograph looking towards at rilling and heavy side cast. Page

16 Single Depth Measurements Bridges and Valley Floors are measured with a sediment probe at reference locations. 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 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 No No sediments at post. Thick willow growth. BR Yes Yes Yes Yes Sediments at post are likely from sidecast material transported from drainage outfall at ECBs under bridge. VF No Yes No No No sediments are at the post, however there are delta deposits upslope of post at toe of fill slope. VF Yes No No No No new sediments at post. Vegetation has established on deposits. VF Yes 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 G culvert repair project. Page

17 Table 3 Center Median Surveys Location Notes CM CM CM CM Heavy and course sedimentation. EC logs need repair Smothered vegetation. Can't find invert of culvert Significant side cast. Median reconstructed Sediment deposition at invert. Photograph looking at culvert and course sediment at CM Page

18 Erosion Control Basin Surveys Visual observations of the storage capacity and sedimentation at Erosion Control Basins are used to indicate the load allocation from Cut Slopes and Bike Path Swales. Maintenance operations had not cleaned out basins prior to the 2013 survey. Table 4 Erosion Control Basin Survey I-70 East Bound Sedimentation Distance to storm water control Notes Clean /23 Full Full 0.1 Small and not adequate capacity. Potential to expand basin upslope and pave shoulder to route sediments. At bridge location Full 0.2 Located east of chain station, potential to expand basin Full 0.5 Small basin Full 1.0 Uncontrolled from Bridge at to culvert Full 0.3 Small basin with large shoulder and potential to expand Full - 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 0.1 Not adequate capacity Clean - Clean between , large shoulder. Page

19 187.4 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. I-70 West Bound Clean Clean - Reverse drainage to ECB at Full 0.1 Limited capacity Full 0.1 Subsurface basin Full 0.25 Two subsurface Full Full 0.2 Series of small basins. Limited capacity Full Full 0.2 Not adequate capacity Full 0.1 Subsurface Full 0.2 Subsurface Full Clean - Adequate capacity, two basins Clean - Small basin. Room for expansion Full Full 0.3 Small basins are full and flat grade. Significant side cast accumulation. Page

20 Bike Path Swales Full 1.0 New curb routes storm water to basin Full 0.3 Room to improve and expand basin in conjunction with shoulder and drainage improvements near Three gullies upslope forming between highway and bike path swale near need repair Clean - 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 Need for sediment basins upslope to control culvert drainage from highway to bike path swale. Photograph is looking upslope near MM Page

21 Photograph shows example of one of the three gullies forming down MM fill slope between I-70 and the bike path. Photograph to the left is looking upslope near 187.5, and right is looking down at EC basin near Area is recommended for drainage and basin capacity expansion. Page

22 V. Sediment Source Load Allocation and Budget Data collected from the 2013 sediment source monitoring efforts were used to input parameters to calculate the Load Allocation. 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). The Sediment Budget was approximately the same between 2012 and The percent fines and the d(50) monitored by the Forest Service show a trend toward improvement, which is reflected in the Channel Bed Storage in the Load Allocation. The loading from Accumulation Under Bridges decreased between 2012 and 2013; due to riparian growth retaining sediments. The category with increased loading is the Fill Slope Gullies; the three new gullies forming between show degradation and sediment transport. The largest contributor in sediment loading is the Cut Slopes along the highway. The limited space for adequate Erosion Control Basin capacity, coupled with the need for more periodic maintenance operations, have contributed to the high sediment load in the budget. Table 5 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 Storage 3 1,570 1,005 Fill Slope Gullies 1, Fill Slopes 1, ,245 Valley Floors 2 1,100 1,100 Cut Slopes 1 2,760 2,870 Accumulation Under Bridges Increased erosion of native slopes Bike path swales 1,2 1, Center Medians Increased Bank Erosion Other 1,2,3 0 0 Sediment Sources TOTAL LA 12,391 12,424 BGC Transport Capacity (TC) 8,600 8,600 BGC Assimilative Capacity (AC) - - Page

23 Exported Sediment Load 1,2,3 13,699 4,987 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 2013, and assumptions in the TMDL. ***Imported and exported load estimates for 2013 reported by CDOT (BGC FY 2013). V. Summary and Discussion Many of the erosion control basins do not have adequate capacity due to the limited space along the highway corridor. There is a need to increase maintenance operations for more regular clean-out of the small ECBs. Periodic maintenance along the highway will help keep sediments from transporting beyond the highway corridor and save money in the long-term associated with larger watershed restoration projects. Periodic maintenance is recommended: 1.) During late May, or immediately after snowmelt; 2.) During late summer after storm events, 3.) During the fall to restore capacity for winter operations. The Basin of Last Resort has filled quickly, likely due to the fill slope failure and culvert blow-outs that occurred immediately after restoring capacity in The Basin of Last Resort is near capacity and planning should foresight restoration within the next few years. Repair at MM is recommended as a priority project. Immediate action is recommended to prevent large scale failure of the fill slope culvert and a slug of sediments from entering Black Gore Creek. Alternatives for the repair at MM should consider: Repair of the Fill Slope culvert(s) Drainage improvements and ECB expansion off the shoulder Expand capacity for WB erosion control. The subsurface basins are too small. Is there potential to route drainage to sediment basin on shoulder? Repair gully stabilization structures on the Valley Floor. Installing temporary BMPs such as erosion control logs, silt fences and drainage improvements are affective at keeping sediments from transporting into the channel; however these require proper installation and annual repair/replacement. For example, the silt fencing under the bridge at was affective at retaining side cast sediment but after two years these were buried completely and now need to be replaced. Erosion control logs that were placed at parallel horizontal intervals across the fill slope were more effective then a single line at the top of the slope. A single line at the top of the slope was buried relatively quickly. Section II Adaptive Management Recommendations (page 1-2) summarizes recommendations for maintenance and restoration projects for summer-fall in Page