Factors Controlling Hydrologic Permanence of Headwater Streams

Headwater streams compose the majority of stream miles within most drainages. Interest in monitoring headwater streams is increasing because these streams are vital linkages between upland land use and downstream water bodies. However, traditional stream assessment tools are often unsuitable because many headwater streams are prone to natural drying. Our objective was to identify physical characteristics of headwater reaches that are indicative of hydrologic permanence, a critical first step in applying a stream assessment. We surveyed 61 reaches along 17 headwater streams (< 2.6 km2) across 4 forests in Indiana, Kentucky and Ohio. Reaches varied in hydrologic permanence over the 2-year study. Exploratory data analysis (CART and discriminant analysis) was used to identify physical parameters for classifying reaches by hydrologic permanence. Drainage area was a consistent parameter discriminating permanence categories and consistently separated ephemeral from perennial and intermittent reaches. Secondary parameters that distinguished intermittent from ephemeral and perennial reaches included bankfull width, maximum pool depth, and channel entrenchment. These factors represent basin and reach scales, suggesting that hydrologic permanence in stream networks should be investigated in a hierarchical context. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.