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Earth and Environmental Sciences Home > Rappahannock Watershed Information > Research Projects > Soil and Drainage Survey of the Hazel Run Drainage Basin

Characteristics of the Hazel Run Drainage Basin

Rachel Hopkins, Junior Economics and Environmental Science Major

Based on the soil type, slope, topography, and vegetation of the Hazel Run drainage basin, storm runoff mostly often enters the channel through shallow subsurface storm flow (SSSF) and Dunne Overland flow. While SSSF may be the most frequent way that storm runoff enters the Hazel Run channel, Horton overland flow is also responsible for channeling some water into Hazel Run. Before understanding how future development will affect the Hazel Run drainage basin and adjacent areas, one must thoroughly understand these three processes of channeling runoff and understand the factors that control these processes.

Based on the included table of soil types in the Hazel Run drainage basin, the category, "S," which represents an area of Dunne overland flow and/or SSSF, is the most frequently appearing category of channel formation. Out of 28 different sections of area (according to soil type) on the map of the basin, these processes account about 40% of the movement of water into channels. According to Dunne and Leopold, SSSF usually occurs in "well drained, deep, and very permeable, and cover steep hillsides bordering a narrow valley floor" like the majority of soil contained in Hazel Run (273). During a rainstorm, water easily infiltrates in the upslope region and only slightly causes a rise in the water table at that point. Near the stream, however, water quickly infiltrates into the water table and causes the level of the channel to rise. According to the classification of soil types and processes of water movement listed in the attached table, this is the process that has the most effect of the Hazel Run channel.

diagram of runoff

Figure 1: Runoff Producing Areas of Hazel Run Drainage Basin.

Yellow = Infiltration and Low Erosion Potential
Brown = Horton Overland Flow
Blue = Dunne Overland Flow
Clear (White) = Infiltration and High Erosion Potential

In those areas of the Hazel Run Drainage basin that have a lot of construction, concrete, and blacktop (#46- Urban land-Udults complex), Horton overland flow (HOF) dominates the movement of water into the channel. Disturbances by humans such as construction and urbanization not only reduce the amount of vegetation anchoring the soil, but they also reduce the level of infiltration and water storage that can occur in those areas. As a result of decreased vegetation, infiltration capability, and storage capacity, areas of urbanization experience drastically increased and quickly occurring runoff in the form of Horton overland flow instead of SSSF or Dunne overland flow.

With this knowledge of how urbanization in an area can drastically alter the natural processes of water movement and how it can alter the level of runoff, it is easy to be pessimistic about future development in areas like Hazel Run drainage basin. Assuming that urbanization will continue to increase in Hazel Run and surrounding areas, HOF is likely to become more noticeable, if not the dominate process of water movement in Hazel Run. Consequences of this increased runoff and faster movement of water to the Hazel Run channel are not pretty. In 50 years Hazel Run could be experiencing damaging floods and high levels of erosion. Not only are these effects terrible in that they destroy the quality of the natural environment, but they pose problems for the economy as well. With increased erosion of the stream banks, the value of property in the area, especially waterfront property will be greatly reduced. Problems with flooding will call for the construction of more sewers and man-made drainage networks, all of which costs the area and the taxpayers a large amount of money. With decreased revenue from property taxes and increased costs for solutions to the flooding and erosion, the area of Hazel Run will be suffering economically as well as environmentally.

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