A watershed scale numerical model of the impact of land use change on bed material transport in suburban Maryland, USA

Abstract

We predict changes in bed elevation and grain size composition caused by urbanization from 1952 to 1996 in the channel network of the Good Hope Tributary watershed. We developed methods for predicting the influence of urbanization on (1) the 1.5‐year peak discharge, (2) the annual sediment supply to the network, and (3) sediment production caused by channel enlargement. The model was calibrated to reproduce bed material yield estimated from a sediment budget. Development caused channel width to increase by a factor of 1.7, and discharge, upland sediment supply, and bed material yield approximately doubled. The longitudinal profile became smoother, and the bed coarsened. After 1996, model boundary conditions were held constant and the simulation continued through 2042. The bed continued to coarsen, and the yield of bed material gradually declined. Sediment production did not approach a steady state value, suggesting that geomorphic recovery from urbanization may require more than 50 years.

A Sediment Budget for an Urbanizing Watershed, 1951‐1996, Montgomery County, Maryland, U.S.A.1

“… Fraction of the Good Hope Tributary Watershed Under Construction for 1951‐1996 (from Lewicki, 2005). …”

“…Lewicki (2005) mapped the locations of buried pre‐settlement soil horizons in four exposed river banks of the Good Hope Tributary (and of other watersheds nearby). At these locations, post‐settlement “Agricultural Age” deposits comprised 50, 40, 58, and 53% of the total height of eroding banks.…”

“…The relief ratio of the watershed, defined as the basin length (the straight‐line map distance between the mouth of the stream and the farthest point on the drainage divide) divided by the maximum relief, is 0.019. The bed of the Good Hope Tributary has an average gradient of 1.33% and it consists mostly of gravel sized sediment (Lewicki, 2005). The banks consist predominantly of sandy mud with <10% gravel (grain size terms are used following the Udden‐Wentworth scale; Lewis, 1984).…”

How urban stormwater regimes drive geomorphic degradation of receiving streams

“…Southern California (Brownlie and Taylor, 1981); Southern Ontario (Annable et al 2012)). More commonly, sediment supply remains elevated above background conditions, a result which has been demonstrated across several physiographic settings (Chin, 2006, Lewicki et al, 2007Pizzuto et al, 2000;Russell et al, 2017;Russell et al, 2019a;Smith and Wilcock, 2015). A more universal phenomenon is that bedload transport tends to increase in urban streams due to increased high flows driven by urban stormwater drainage (Bledsoe and Watson, 2001).…”

Numerical simulation of the impact of sediment supply and streamflow variations on channel grain sizes and Chinook salmon habitat in mountain drainage networks

“…The influence of sediment pulses or land‐use changes on channel morphology, as well as sediment delivery mechanisms to channels, have been numerically modeled (e.g. Lancaster et al ., , ; Lisle et al ., ; Cui et al ., ; Cui and Parker, ; Lewicki et al ., ; Patil et al ., ). Benda and Dunne (, ) developed a sediment routing model for mountain drainage networks to understand the effects of chronic, landslide and debris flow sediment sources.…”