Meacham Creek Groundwater Model Development and Phase I Modeling

In summer 2011, the Umatilla Tribe completed a large channel restoration project along a one-mile (1.6 km) reach of Meacham Creek in Oregon using PCSRF and BPA funding. Meacham Creek is an important steelhead and salmon spawning tributary to the Umatilla River. This restoration effort included levee and dike removal, channel realignment (re-meandering), reshaping the adjacent floodplain, addition of large woody debris and rock for habitat complexity, and re-establishment of vegetation with the specific objective of increasing floodplain connectivity and hyporheic exchange.

Under this post monitoring project, the effectiveness of the restoration work on surface and groundwater temperature and hydrology was conducted. A main feature of the monitoring work was the installation of groundwater wells with recording level and temperature loggers deployed in them, and deployment of surface water temperature loggers to document hydrological and water temperature at the restoration site before and after the restoration project (see Figures 1&2 in the report). The PCSRF funding provided funding for database development; conceptual groundwater model development and revision; groundwater model development, implementation, and revision; and Phase I GW model reporting. BPA funding was used for other tasks.

Key project findings:

1. Channel restoration along Meacham Creek has altered hyporheic residence time distribution by increasing heterogeneity and gross hyporheic exchange has also increased.
2. Post-restoration hyporheic exchange likely has an increased effect on stream temperature. Furthermore, hyporheic zone temperature heterogeneity has increased as function channel realignment and concomitant shifts in hydrology.
3. Aquatic habitat has benefitted mainly from an increase in sites of hyporheic upwelling along the restored reach and the formation of spring-fed alcoves as the channel adjusts over time.

The primary benefits to ESA-listed summer steelhead and bull trout, spring Chinook salmon, and other resident fish are likely increased temperature heterogeneity as a result of shifts in hyporheic hydrology from floodplain-channel restoration actions that occurred in the project area that resulted in an increase of intermediate length flow paths (~10 – 30 day residence time) and increased hyporheic exchange. These shifts in hydrology likely increased overall temperature heterogeneity and the presence of thermal refugia. Newly formed upwelling spring sites and increased alcove habitat following 2011 restoration have resulted in increased quality and quantity of fish holding and rearing habitat. Formation of spring-fed alcoves adds to both physical and temperature habitat heterogeneity and creates obvious habitat for all life stages of salmonids in all seasons. While surface water is not technically cooled, water buffered to its mean daily temperature is relatively cool compared to peak daytime temperatures. Similarly in wintertime, buffered and lagged water will be relatively warm and form a thermal refuge from cold winter water temperature.