RELATING WATER TEMPERATURE-DERIVED FLOW PRESENCE/ABSENCE TO COLLUVIAL VALLEY SECTIONS IN A HEADWATER STREAM

The causes and dynamics of the discontinuous expansion and contraction of stream networks are not well understood and can be difficult to predict. However, some factors that might control stream expansion and contraction are precipitation, subsurface storage, and critical zone structure. The purpose of this study was to determine the effect of colluvial deposits in stream valleys on surface flow presence. This study took place in the 50 ha McDonald Hollow catchment in the Valley and Ridge physiographic province in southwest Virginia. To address this question, we first mapped colluvial deposits in the stream network. Colluvial deposits were mapped throughout the stream network using a digital elevation model (DEM). Thirty temperature sensors were installed throughout the 2.14 km stream network and set to record temperature every 10 minutes. Sensors were placed in areas of permanent surface flow, fluctuating surface flow, and above the stream. One way to potentially remotely detect water presence in a stream is through the analysis of water temperature fluctuations throughout the stream network. These data were used to determine if a particular point in the stream network had present or absent surface flow each day by using a set deviation of the temperature from a sensor with known permanent flow absence/presence. The sensor locations and the status of their presence or absence of flow at a particular time were compared to the locations of colluvial deposits in the watershed. Patterns in the areas where stream contraction occurs and locations of colluvial deposits suggest that colluvial deposits may cause an absence of surface flow in streams. Furthermore, the large temperature fluctuations of the sensors that were in areas without surface flow compared to those that were in areas with surface flow suggests that temperature sensors can be used to detect flow presence.