Stream temperatures in the Driftless Area
The Driftless Region is blessed with an exceptional coldwater fishery (native brook trout and non-native brown trout). Based on statistical modeling, it has been predicted that over the next 50 years brook trout will virtually disappear from the region and areal extent of brown trout will decrease significantly. However, these predictions do not account for potentially significant increases in groundwater recharge and hence in baseflow as a result of likely increases in fall through spring precipitation and potential decreases in winter frost. Nor do they account for the fact that baseflow in the Driftless Region is due mainly to thousands of springs, many of which are supply streams with relatively small drainage areas (e.g., less than 10 km2). Empirical evidence suggests that flow from these springs as well as from in-channel seeps persists at anomalously high rates during droughts, such as the severe drought of 2012.
We are conducting field studies and modeling to investigate the factors affecting the spatial distribution of springflow and diffuse groundwater discharge to streams in the Driftless Region. The major factors appear to be landuse and stratigraphy. We are collecting continuous streamflow and water temperature data at a number of locations in the watersheds that begin at a particular headland. We are also constructing a groundwater model of the region. Based on the data and modeling we expect to be able to develop accurate predictors of baseflow for the entire Driftless Area.
We have found that the spatial variation in baseflow at 12 locations correlates very strongly with fraction of watershed in hillside. The next step is to obtain better information on the local stratigraphy.
This project will provide a better understanding of the factors controlling the spatial distribution of baseflow and stream temperatures in the D.A., and provide more accurate information on the likely changes in stream temperatures in the D.A. due to climate change.