2008 BES Annual Meeting Presentation and Poster Abstracts
Quantification of Hydraulic Conductivity of Streambeds throughout the Gwynns Falls Watershed and Surrounding Area
Co-Authors: Peter Lapa-Lilly, Sarah Poole, Claire Welty
Abstract: The objective of this work was to compile a dataset of streambed hydraulic conductivity values, along with the base-of-banks width, width of water present, depth of water and streambed thickness, in order to calculate “streambed conductance," which is an input parameter required by the MODFLOW groundwater model. Hydraulic conductivity values of streambeds within and around the Gwynns Falls watershed were measured in situ using a falling head permeameter, at an average depth of 8.7 cm below the bed surface. Over 100 measurements were taken at 42 sites during a three-week period in July 2008. The study area spanned 603 km^2 and covered a gradient of urbanization from the rural areas surrounding the upper Gwynns Falls to the highly urban downtown Baltimore region. Hydraulic conductivity was measured three times across the stream channel at each site and averaged to a single value to account for spatial variability. Results were then corrected to a water temperature of 20°C. The data were log-normally distributed, ranging from 1.41 x 10^-3 cm/sec to 5.62 x 10 ^2 cm/sec with a mean value of 1.31 x 10^-2 cm/sec and standard deviation of 9.10 x 10^-3 cm/sec. Average depth of bed material above bedrock was found to be 37.8 cm, with a range of 9.50 cm – 94.5 cm and a standard deviation of 22.5 cm. A variety of streams was sampled, including minor tributaries near the headwaters and several main stem branches.