EVALUATING THE SLOPE-AREA METHOD TO ACCURATELY IDENTIFY STREAM CHANNEL HEADS IN THREE PHYSIOGRAPHIC REGIONS

Estimation of stream channel heads is an important task since ephemeral channels play a significant role in the transport of sediment and materials to perennial streams. The slope-area method utilizes digital elevation model (DEM) and related information to develop slope-area threshold relationships used to estimate the position of channel heads in the watershed. A total of 162 stream channel heads were mapped across the three physiographic regions of Alabama, including the Southwestern Appalachians (51), Piedmont/Ridge and Valley (61), and Coastal Plains (51). Using Geographic Information System and DEM, the local slope and drainage area for each mapped channel head was calculated and region-specific models were developed and evaluated. Results demonstrated the local slope and drainage area had an inverse and strong correlation in the Piedmont/Ridge and Valley region (r(2) = 0.71) and the Southwestern Appalachian region (r(2) = 0.61). Among three physiographic regions, the weakest correlation was observed in the Coastal Plain region (r(2) = 0.45). By comparing the locations of modeled channel heads to those located in the field, calculated reliability and sensitivity indices indicated model accuracy and reliance were weak to moderate. However, the slope-area method helped define the upstream boundaries of a more detailed channel network than that derived from the 1:24,000-scale National Hydrography Dataset, which is commonly used for planning and regulatory purposes.