![]() ![]() The department offices are located at 915 Spring Street, Friday Harbor, WA 98250. San Juan County’s Public Works Department constructs and maintains county roads, designs and constructs storm water facilities, and plans and contracts for solid waste services. Krista Davis, Stormwater Engineering Technician, (360) 370-0533Ībout San Juan County’s Public Works Department New trees will be added along the drainage and trail to replace those removed by the construction. The project will remove seven mid-sized trees (5 crabapple, 1 apple, and 1 red alder) currently growing over a sanitary sewer main and in the path of the new drainage swale. All work is being conducted within the County road right of way and easement. The drainage will be planted with native vegetation, including trees, shrubs, and grasses. In addition to the drainage, the parallel parking along the road will be improved and a gravel trail and bridge crossings will be installed to provide safe pedestrian access to the Farmers Market. The project is funded by a grant from the Department of Ecology and the County’s Clean Water Utility. The Lopez Village Stormwater Improvement Project will upgrade the eroding ditch along the east side of Village Road and improve storm water quality and manage flooding. The Department of Environmental Stewardship and Project Manager Krista Davis would like to thank the Lopez community for their patience and support throughout the planning, design, and construction of the new stormwater channel. The road is currently open to the public. Tree and shrub planting will commence in early spring. In the meantime, a temporary divider will be installed to maintain the integrity of the trail over the wintertime. The new parking area will be chip sealed next year so the gravel walking trail will be more defined. Crews plan to clean up and prepare to leave the project site.Crews will install the vortex weirs and split rail cedar fence.The new bridge has been installed and rock lining has been completed. This new channel is a major improvement for stormwater conveyance and capacity in Lopez Village. The Public Works crew has completed the new stormwater channel which is currently in-use and performing well - especially during recent rains. In the context of stormwater controls to improve water quality, a grassed swale is a vegetated, open-channel management practice that treats and reduces stormwater flows for a specified water quality volume. December 5, 2022– San Juan County Public Works is pleased to provide the public with updates on the Lopez Village Stormwater Improvement Project. This being said, regardless of soil type, you'd want to maintain as much tree'd vegetation as possible and use a long armed shovel and small compaction equipment. Given the overall vertical drop and slope of the hill, I would assume that you would assume that you would want to disturb as little as possible on the slope to maintain slope stability. Outside the scope of the storm sewer, constructability may be an issue. Placing perforated pipe at the bottom of the slope may be something you would want to look at in more depth and also consult a geotechnical engineer as this added moisture may be a cause of toe failure down the road. Considering a single section of HDPE or Cobra Lock PVC may be an option to consider. It may be beneficial to consider pipe materials as well in this case due to 1) higher velocities and 2) Given the slope, there may be a possibility for our pipe joints to separate. As cvg has said your best best would be to size your pipe smaller to ensure full flowing conditions with some kind of energy dissipation located at the downstream end if required. I live in a rather hilly region and have completed several of these types of designs. RE: Stormwater Conveyance Down a Steep Slope danenviro (Civil/Environmental) I have seen these used with some success as down drains on large slopes and carrying larger flows than what you have. ![]() You might be better off with a concrete lined ditch, shotcrete or broomed finish and maybe step it. With this slope a larger pipe will not flow full and will not help with dissipating much energy. Usually I require at least 15 or 18 inch outlet pipe to keep clogging down to a minimum. With either 6 or 10 you will have to screen the inlet to keep the trash out or it will plug. With this slope you could get by with a much smaller one, maybe 6 inch or smaller if you can keep it flowing full. To burn off more energy you might consider using a smaller pipe. In addition, constructing a manhole on this steep a slope will be very difficult. However, if you wish to construct a drain with drop manholes - assuming a 4 foot drop, you would have 20 manholes or 1 every 12 feet. Well, you have very low flows and not a huge hill. ![]()
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