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

Abstract

Despite widespread interest, few sediment budgets are available to document patterns of erosion and sedimentation in developing watersheds. We assess the sediment budget for the Good Hope Tributary, a small watershed (4.05 km2) in Montgomery County, Maryland, from 1951‐1996. Lacking monitoring data spanning the period of interest, we rely on a variety of indirect and stratigraphic methods. Using regression equations relating sediment yield to construction, we estimated an upland sediment production of 5,700 m3 between 1951 and 1996. Regression equations indicate that channel cross‐sectional area is correlated with the extent of development; these relationships, when combined with historical land use data, suggest that upland sediment yield was augmented by 6,400 m3 produced by enlargement of first‐order and second‐order stream channels. We used dendrochronology to estimate that 4,000 m3 of sediment was stored on the floodplain from 1951‐1996. The sediment yield from the watershed, obtained by summing upstream contributions, totals 8,100 m3 of sediment, or 135 tons/km2/year. These results indicate that upland erosion, channel enlargement, and floodplain storage are all significant components of the sediment budget of our study area, and all three are approximately equal in magnitude. Erosion of “legacy” floodplain sediments originally deposited during poor agricultural practices of the 19th and early 20th Centuries has likely contributed between 0 and 20% of the total sediment yield, indicating that these remobilized deposits are not a dominant component of the sediment yield of our study area.

Impact of Climate and Land Use Change on Streamflow and Sediment Yield in a Snow‐Dominated Semiarid Mountainous Watershed

“…Our study projected the mean daily sediment load at the Big Cottonwood Creek site to increase 1.4 tons/day (≈3.8 t/km 2 /yr) in 2040s to 1.7 t/day (≈4.9 tons/km 2 /yr) in 2090s. The predicted sediment yields per watershed area are consistent with the results reported by Allmendinger et al (), which vary from 0.2 t/km 2 /yr in the Colorado River to 6.3 × 10 3 tons/km 2 /yr in Tributary at Gwynns Falls, Maryland. The predicted increase in sediment yield has implications for river and floodplain managers, as increased maintenance of waterways will be required in areas prone to deposition.…”

Closing the Gap Between Watershed Modeling, Sediment Budgeting, and Stream Restoration

“…Alluvial floodplains typically become recognizable features along second-or third-order channels [Allmendinger et al, 2007]. Variations in the actual limits are strongly influenced by the history of upland sediment supply, watershed hydrology, valley profile, bedrock control, and artificial structures, including dams [Jain et al, 2008].…”

Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA

“…In response to this incongruity, some have argued that increased stormwater runoff from urbanization, possibly in combination with a decrease in upland sediment supply, is the cause of widespread modern channel incision and stream bank erosion [18,26,42,43]. As with associating the coincidence in the timing of agriculture with high sediment yields, linking incision and bank erosion with either stormwater runoff or reduced sediment supply is done by association with upstream, contemporaneous land use.…”