|
Technical Notes
<br />iiensive soil amendments to restore their intended
<br />tion.
<br />The second key implication of compaction relates
<br />to the objectives for local erosion and sediment control
<br />plans during construction. From a watershed stand-
<br />point, these plans should not only focus on preventing
<br />soil loss, but go further to prevent soil compaction. Any
<br />reduction in clearing, grading and construction access
<br />will provide a stormwater management benefit. Un-
<br />cleared and ungraded portions of the site represent an
<br />important "hydrologic reserve area," and erosion and
<br />sediment control plans should clearly demarcate the
<br />limits of disturbance over as much of the site as possible
<br />to retain these. Hydrologic reserves can include wet-
<br />lands, conservation areas, buffers, setbacks, open space,
<br />and even portions of individual lots. However, draw-
<br />ing the limits of disturbance on a plan is much easier
<br />than actually enforcing them in the field, so increased
<br />contractor training and fencing are essential. Commu-
<br />nities should also carefully reevaluate their current
<br />compaction requirements and grading standards to
<br />ensure that they only compact those areas of the site
<br />that are absolutely necessary, and otherwise promote
<br />the retention of undisturbed soils.
<br />The third implication of urban soil compaction is
<br />t severe soil compaction fundamentally alters the
<br />hydrology of a site, and makes many pervious areas
<br />function more like impervious ones. This suggests that
<br />engineers will need to explicitly incorporate the ef-
<br />fects of soil compaction into their models that predict
<br />the changes in runoff as a result of development. The
<br />challenge is that while it is relatively easy to predict the
<br />increase in bulk density caused by construction, it is
<br />much harder to predict precisely how much this in-
<br />crease in bulk density will increase the runoff coeffi-
<br />cient or curve numbers for pervious areas. More re-
<br />search is urgently needed to characterize runoff from
<br />lawns and landscaped areas on compacted urban soils.
<br />Until better data are available, it seems prudent to
<br />model the runoff from pervious areas differently. For
<br />example, it may be advisable to adjust runoff coeffi-
<br />cients upwards for compacted pervious areas (by ap-
<br />proximately 0.1 to 0.15) or, when using the NRCS TR-
<br />55 model, to automatically shift curve numbers (CN)
<br />upward by at least one hydrological soil group (HSG)
<br />when a site is cleared (i.e., if the original pervious area
<br />was a B soil, model it as if it were a C soil). An even
<br />larger shift is probably justified if the area is planned to
<br />e an athletic field or a new lawn.
<br />In summary, watershed managers should bear in
<br />mind that the quality of soils is inextricably linked to
<br />the quality and quantity of water. Greater efforts to
<br />prevent or reduce the compaction of soil quality that
<br />results from construction are an important element of
<br />any urban watershed protection strategy. —TRS
<br />Editor's Note: Thanks are extended to Chris Smith and
<br />David Friedman, who supplied data and information
<br />for this technical note.
<br />Contact: Chris Smith: 732 - 246 -1171 ext 175.
<br />References
<br />Bethlenfalvay, G. and R. Linderman. 1992. "Mycor-
<br />rhizae in Sustainable Agriculture." ASA Special
<br />Publication No. 54. American Society of
<br />Agronomy. Madison, WI.
<br />Craul, P. 1994. "Urban Soils: An Overview and Their
<br />Future." pp 115 -125 in The Landscape Below
<br />Ground. Proceedings of International Workshop
<br />on Tree Root Development in Urban Soils. Inter-
<br />national Society of Arboriculture. Champaign,
<br />Illinois.
<br />Friedman, D. 1998. Personal communication. District
<br />Director. Ocean County Soil Conservation Dis-
<br />trict. Forked River, N.J.
<br />Legg, A. R. Bannerman, and J. Panuska. 1996. "Varia-
<br />tion in the Relation of Rainfall to Runoff from
<br />Residential Lawns in Madison, Wisconsin, July
<br />and August, 1995." U.S. Geological Survey Water
<br />Resources Investigation Report 96 -4194. With
<br />the Wisconsin Department of Natural Resources.
<br />Madison, WI.
<br />Lichter, J. and P. Lindsay. 1994. "Soil Compaction and
<br />Site Construction: Assessment and Case Studies."
<br />pp. 126 -130 in The Landscape Below Ground.
<br />Proceedings of International Workshop on Tree
<br />Root Development in Urban Soils. International
<br />Society of Arboriculture. Champaign, Illinois.
<br />Morris, L. and R. Lowery. 1988. Influence of Site
<br />Preparations on Soil Conditions Affecting Stand
<br />Establishment and Tree Growth." Southern Jour-
<br />nal of Applied Forestry. 12(3): 170 -178.
<br />Pitt, R. 1992. Small Storm Hydrology. SLAMM Docu-
<br />mentation.
<br />Randrup, T. 1998. "Soil Compaction and Construction
<br />Sites." pp. 146 -154 in The Landscape Below
<br />Ground. II. Proceedings of International Work-
<br />shop on Tree Root Development in Urban Soils.
<br />International Society of Arboriculture. Champaign,
<br />Illinois.
<br />Schueler, T. 1995. "The Peculiarities of Perviousness."
<br />Watershed Protection Techniques. 2(1): 233 -238.
<br />Smith, C. 1999. Soil Compaction Findings and Inter-
<br />pretation. Natural Resources Conservation Ser-
<br />vice.
<br />Wignosta, M., S. Burges, and J. Meena. 1994. "Model-
<br />ing and Monitoring to Predict Spatial and Tempo-
<br />ral Hydrological Characteristics in Small
<br />Catchments." Water Resources Series Technical
<br />Report #137. University of Washington. Dept. of
<br />Civil Engineering. Seattle, WA.
<br />Watershed Protection Techniques Vol. 3, No. 2 January 2000
<br />
|