This week, Summit County’s design-build team of Ecological Resource Consultants/Tezak Heavy Equipment (ERC/Tezak) continues major earthwork operations on the Swan River Restoration project site. As crews continue to excavate the new channel west towards Rock Island Road, they are encountering groundwater seeping out of the dredge gravels. This condition is visible in the photo below.
The photo below is from just around the bend, behind the machinery in the photo above.
From a stream restoration standpoint, this groundwater condition is excellent news for maintaining water in the channel once the project is complete, because it will result in a condition known as a “gaining stream” as opposed to a “losing stream.” Gaining streams intersect groundwater, which helps keep water in the channel more permanently. Losing streams sit above groundwater (year-round, or seasonally) and therefore “lose” their water through the channel bottom, into the ground. The existing condition within the project site is a mix of both, which is why the upstream end of the Swan River dries up seasonally as localized groundwater elevations drop.
However, digging into groundwater also presents water management challenges while construction is ongoing. As exposed groundwater (now surface water) passes through the restoration project site, it picks up fine-grained sediment, which causes downstream water in the Swan River to look silty. This silty condition is called turbidity. The photo below shows turbid water flowing through the new channel. Once work is complete, this water will be clear.
Yesterday, representatives from Summit County and ERC/Tezak met onsite with project partner representatives from Colorado Parks and Wildlife (CPW) to discuss the project status, as well as any impacts temporary turbidity conditions might have downstream from the project site. Based on coordination and communication with fisheries biologists and stream restoration experts, we understand that this temporary turbidity condition should have negligible impacts on downstream stream health. Fish and insect species living in the Swan River are well-adapted to handle short term turbidity, which is common seasonally, as well as when concentrated rainfall events, such as strong thunderstorms, pass through the area. During our site visit with CPW, we also witnessed mayflies hatching downstream of the project site, which is an excellent indicator of stream health. These “macroinvertibrate” insects are very sensitive to small changes in stream conditions and are an important food source for fish. For all of these reasons, we remain confident that though the water may look turbid while construction is occurring, the overall stream ecology remains healthy and good. Turbidity will likely be a regular occurrence while excavation is occurring onsite, but should improve when earthwork ceases at the end of each day and week.
The photo below the existing Swan River channel adjacent to Tiger Road. Crews have installed periodic check dams along the channel to help slow down flows and encourage sediment to "drop out" of the water as it flows downstream.
With channel construction moving ahead quickly, crews are optimistic that they can begin installing riffles, pools, and other habitat features this week. In addition, ERC/Tezak anticipates material export to recommence from the site starting next week (week of August 1st). Stay tuned for updates.
Work is scheduled to continue through November 2016, followed by a winter shut-down period, before recommencing in spring 2017. Additional information about Swan River Restoration Project is available at RestoreTheSwanRiver.com as well as on the Open Space and Trails Special Projects web page. If you have additional questions about the restoration project, you can contact Summit County Open Space and Trails Director Brian Lorch, or Open Space and Trails Resource Specialist Jason Lederer, or call 970.668.4060.