Fluvial erosion, sedimentation, and hydraulic geometry in the contributing watershed of Old Woman Creek National Estuarine Research Reserve

"Natural stream flow and sediment load have affected Old Woman Creek and its estuary for eons. Recently, humans have superimposed their effect on the watershed. The future will bring even greater human modification including increased suburbanization and a new highway bridge across the National Estuarine Sanctuary. The primary objective of this study was to establish baseline sediment and discharge data to permit the monitoring of future change within the fluvial system. Eight cross-sectional profiles were monumented and surveyed for future erosion assessment. Nine other cross-sections were repeatedly surveyed while collecting discharge, sediment concentration, sediment yield, water depth, and stream velocity data. Analysis of these data led to formulation of mathematical relationships between a station's depth and discharge as well as sediment yield and discharge. Further analyses showed that the magnitude and variability of discharge during a particular storm was primarily a function of geomorphologic province, drainage area, estuary level, and human impact. A maximum of 153 cubic feet/second was recorded entering the estuary. The magnitude and variability of sediment concentration during a particular storm was a function primarily of human disturbance of the land and, secondarily, of soil erosion potential and channel composition. Large amounts of sediment were transported during brief periods of intense precipitation; on 2/25/85, 14.5 ounces/second were contributed to the estuary by the creek. A permanent stage recorder should be established to continuely monitor water contribution to the estuary from the creek."