Snake March Flow and Water Quality Monitoring

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Owner: California Department of Fish and Game
Location:
 Galt, California
Funding Source:  The Nature Conservancy
Completion Date: Ongoing

Stilling well and water level logger at Snake Marsh.

The Nature Conservancy (Conservancy), as a partner of the Cosumnes River Preserve (CRP), has hired Davids Engineering to provide engineering hydrology and field services including flow and water quality monitoring for Snake Marsh, a 160-acre freshwater perennial wetland on CRP land. Snake Marsh is named for the giant garter snake (GGS, Thamnophis gigas), a state and federal threatened species that lives there, along with a host of other wetland species. GGS is an aquatic snake and requires aquatic habitat throughout its active season, typically April through October.

The water supply for Snake Marsh is highly altered, and during summer months it is completely dependent on agricultural runoff from irrigation and aquaculture. Water depths vary seasonally, from about 1 meter or less in the summer to several meters during winter or spring floods. Perennial ponds at the marsh become isolated in the summer, fragmenting and isolating the snake population. There is concern that during dry years, ponds could go completely dry, stranding and potentially starving large portions of the population. Better understanding of the hydrology of the marsh could allow for better assessment of risks to the GGS, as well as the development of management responses to improve habitat conditions.

In addition to water quantity concerns, there is concern that water quality at the marsh could pose a threat to fish and other species upon which the GGS preys. In particular, the presence of invasive plant species, whose growth is supported by nutrients in inflows to the marsh, may lead to depletion of dissolved oxygen. Better understanding of water quality in the marsh and for the inflows to the marsh could also inform management responses to improve habitat conditions.

Based on existing knowledge of the hydrology and ecology of the Snake Marsh, the following objectives were identified:

  • Characterize late spring to early fall surface water hydrology, with particular emphasis on inflows originating as irrigation runoff and aquaculture discharge.
  • Characterize how actual surface hydrology affects marsh water levels.
  • Increase understanding of marsh water quality as it relates to GGS health and invasive plant growth through strategic sampling of important water quality parameters.

In order to satisfy the objectives, Davids Engineering is developing a surface water balance for the marsh through extensive monitoring of inflows to the marsh and water levels in perennial ponds that represent critical GGS habitat. Additionally, Davids Engineering is conducting periodic water quality monitoring to evaluate threats to the GGS food supply in the ponds.  As an added component, Davids Engineering has trained TNC staff in the collection of flow measurement data using standard stream gaging procedures as well as collecting water quality samples and performing laboratory analysis of the samples.

Western Pond Turtles at Snake Marsh.

The primary method of flow monitoring for the project consists of periodic measurements of inflows to the marsh using a SonTek FlowTracker acoustic Doppler velocimeter, coupled with continuous monitoring of water levels at strategic locations including perennial ponds and inflow locations. Additionally, various sensors have been deployed to monitor the presence and duration of tailwater inflows to the marsh as well as operation of a groundwater well used to irrigate fields draining to the marsh. Water quality samples are being collected and analyzed for multiple parameters using a combination of field and laboratory tests.