USING A STREAMBED TEMPERATURE SENSOR ARRAY TO STUDY GROUNDWATER CONTRIBUTIONS IN A SMALL STREAM

Streambed temperature mapping has come to be seen as a useful tool for understanding the interactions between groundwater and surface water. Knowledge about these interactions can help public and private resource managers determine resource allocations and needs as well as being a tool for implementing resource development. In an effort to better understand groundwater contributions to Chadron Creek, a small stream in northwestern Nebraska, two in situ temperature sensor arrays were installed in separate 500m reaches of the stream. The arrays consisted of two sets of 50 HOBO Pendant Temperature Loggers that were installed at uniform distance and depth throughout both reaches. To maintain consistency across the data the sensors were also programmed such that they had the same start time, sampling interval and sampling period. The sensors were collected at the end of the 20 day collection period and the temperature data were analyzed to determine simple diurnal and seasonal statistics, such as mean and range. The results from these analyses reflect the expected pattern of suppressed diurnal temperature cycles in effluent reaches as compared to non-effluent reaches of the stream. This is a result of the constant temperature of the groundwater damping the penetration (into the streambed) of the temperature cycle that is heavily expressed in surface water. Effects of seasonal trends and events such as surface precipitation were also visible in the streambed temperature data. When mapped, the diurnal temperature ranges highlight the steady increases and decreases in temperature that represent gaining or losing reaches. The geographical and temporal extent of the arrays help to view these transitions on a larger scale while maintaining a relatively high sampling resolution. Utilizing in situ temperature sensor arrays appears to be a cost effective method for determining reaches of high exchange and ground water influence. Additional work is needed to understand the effects streambed heterogeneity and surficial features exert on streambed temperature variation in Chadron Creek when using single sensor arrays. Additionally, further efforts should be made to use a multi-sensor (vertical) array at the same site or in conjunction with a single sensor array.