Effects of construction on fluvial sediment, urban and suburban areas of Maryland

Abstract

The equivalent of many decades of natural or even agricultural erosion may take place during a single year from areas cleared for construction. Areas undergoing rapid development near Baltimore, Maryland, and Washington, D.C., lie on the Coastal Plain and Piedmont, with slopes generally of 1‐10% but sometimes of 20% and more. Soil is deep, and the annual precipitation of 42 inches (1100 mm) is evenly distributed, with high summer intensities. Average sediment yield is 200–500 t/mi2/yr (80–200 t/km2/yr), with predominantly wooded watersheds supplying sometimes even less. Intensive farming 50–80 years ago caused yields up to 1000 t/mi2/yr (400 t/km2/yr), but such high yields are no longer present owing to the continuous decline of farm acreage in the metropolitan periphery. Sediment concentrations from areas undergoing construction ranged from 3000 to over 150,000 ppm, whereas in natural or agricultural catchments the highest comparative concentration was 2000 ppm. In terms of annual values, yields from construction areas range from several thousand to a maximum of 140,000 t/mi2/yr (i.e., up to 55,000 t/km2/yr) from a small area. Total yield declines with increasing drainage area as a result of dilution from waters draining urban and other land not actually under construction. Observations demonstrate that sediment storage occurs on construction sites as well as in valley bottomlands. Actual yields from a given unit surface may be even larger than those derived from measurements in streams. Data on erosion from roadcuts in Georgia, when converted to soil loss per area, result in sediment yields similar to those from building sites: 50,000–150,000 t/mi2/yr (20,000–50,000 t/km2/yr), and local measurements indicate depths of erosion on roadcuts of 0.1–0.2 ft (3–6 cm) over time intervals of generally less than one year. Imposition of large quantities of sediment on streams previously carrying relatively small quantities of primarily suspended material produced deposition of channel bars, erosion of channel banks as a result of deposition within the channel, obstruction of flow and increased flooding, shifting configuration of the channel bottom, blanketing of bottom‐dwelling flora and fauna, alteration of the flora and fauna due to changes in light transmission and abrasive effects of, sediment, and alteration of species of fish due to changes produced in the flora and fauna upon which fish depend. Analysis of building permit records showed that: (1) 50% of construction sites were open for eight months, 60% for nine, and 25% for more than one year; (2) contrary to expectations, construction activity is practically constant throughout the year, with about 84% of all sites being open in any one month; (3) the average size of a construction site for one permit‐bearing building is 14,400 ft2 (1340 m2), a value that remained constant during the last decade. These findings, combined with statistics on highway construction, indicate that in four Maryland counties covering expanding metropolitan regions adjacent to Baltimore a...

Effects of antecedent hydrologic conditions, time dependence, and climate cycles on the suspended sediment load of the Salinas River, California

“…where Q SS (Q) is the constituent discharge (in this case suspended sediment) as a function of discharge, and f (Q) (Q) is a representation of the probability density function (pdf) of discharge 24 u n c o r r e c t e d , a c c e p t e d (Wolman and Miller, 1960;Wolman and Shick, 1967;Klonsky and Vogel, 2011). Effective discharge is the value of discharge that results in the maximum value of e(Q) for a given transport constituent.…”

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

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Characterization of Stream Meanders for Stream Restoration

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