Excessive in-stream water temperature is the most frequent water quality impairment in Southeastern Oregon, and concerns have arisen over the impact of water diversion for flood irrigation on summer in-stream temperature extremes. We recently completed a study designed to document: 1) the impact of flood irrigation on seasonal temperature dynamics of a meadow stream (Rosgen C class) in southeastern Oregon and 2) changes in groundwater depth in the surrounding meadow and seasonal in-stream discharge. We placed water thermistors (temperature recorders) within the channel upstream, downstream, and within the irrigated reach of the study stream and recorded hourly temperatures from June through August. Discharge was recorded at each water temperature station, and meteorological information was recorded at a weather station placed near the center of the meadow. Groundwater depth was monitored along 5 transects within the irrigated reach of the stream. Transects contained 10 wells with the first well located within 1m of the stream; subsequent wells were spaced at 15 m intervals along an azimuth running perpendicular to the stream. Wells were monitored bi-weekly from May through September. Pre-treatment (non-irrigated) data were recorded in 2002 and post-treatment data in 2004 (irrigated April – July 1). Growing season (June-August) air temperatures were similar between years and the groundwater table remained higher throughout the growing season with flood irrigation. Data analysis is ongoing, but preliminary results suggest that high early season discharge can be prolonged with flood irrigation and that flood irrigation helps buffer water temperature from the controlling influence of high ambient air temperatures.
Many small meadow streams in southeast Oregon are water quality impaired due to excessive summertime water temperatures, often associated with a lack of overhead cover (e.g., shade from woody vegetation). A lack of overhead cover is often associated with excessive browsing of streamside willows by both domestic livestock and wildlife species. We tested the feasibility of using artifical shading (cut western juniper) to ameliorate summer water temperature extremes on high elevation meadow streams. Our results suggest that artificial shading decreased maximum stream water temperature by 2oC and decreased the influence of air temperature on stream temperature fluctuations. This work indicates that shading can influence stream temperature dynamics and provides managers with a technique for reducing summer temperature extremes of high elevation meadow streams. Additionally, the frequency of browsing on streamside willows was greatly reduced with juniper cover (compared to open) suggesting that our treatments may allow for willow growth and expansion, providing a natural shade source over time.
Matney, C.A., C.S. Boyd, T.K. Stringham. (Accepted). Willow herbivory following application of artificial cover using felled juniper. Rangeland Ecology and Management
Matney, C.A. 2004. Placement of Felled Western Juniper Trees Over a Stream Channel: Effects on Water Temperature, Streamside Willow Shrubs, and Redband Trout. M.S. Thesis, Oregon State University, Corvallis.
Matney, C.A., C.S. Boyd, and T.K. Stringham. (in press). Using felled juniper to exclude willows from herbivory. In 2004 Progress Report. Eastern Oregon Agricultural Research Center, Burns, OR.