AWRI Information Services Center
York Creek Management Plan - Critical Areas
5. Critical Areas
An early step in determining the type and location of implementation activities is the delineation of critical areas within the watershed. Critical areas are defined as those geographic areas of the watershed that have the greatest potential to deliver the greatest quantities of pollutants. In order to determine which areas could be described as such, AWRI assembled and generated numerous data and map layers. These layers included topographic information, proximity to the stream, current land use, flooding frequency, and the soil K factor. (The K factor is the susceptibility of a soil to sheet and rill erosion, as determined by the county soil survey.) Two examples of the data analyzed, the flooding frequency and the potential for sheet and rill erosion, are shown in Figures 17-18.
Using the varied information in numerous combinations, AWRI determined critical areas for the watershed. These areas were determined by first establishing a 200 foot buffer along either bank of the stream and tributaries. Flooding frequency is another factor related to the proximity to the stream, and this information, as determined by the soil survey, was included.
In addition, the impact of Alpine Avenue was considered. The Alpine Avenue corridor is one of the fastest growing commercial areas in Kent County, if not the state. Using IDRISI GIS, AWRI generated a 600 foot wide strip on either side of the avenue, and considered all areas within the buffer as critical areas. The depth was selected to accommodate future commercial setbacks along the avenue, which history has shown to be significant contributors of sediment to the stream system. Also, stormwater from the pavement is directly conveyed to the stream, and the degree of imperviousness along the corridor warrants the consideration of the entire corridor as a critical area.
A map overlay method was then used with the IDRISI GIS to combine those areas that are not currently built up and have a high potential for sheet and rill erosion. This combined data layer was then merged with the flooding information and the buffer areas for the final delineation of critical areas (Figure 19).
The rapid rate of development within the watershed became particularly apparent in the determination of critical areas. After the critical areas had been determined, the permit application process began at the City of Walker regarding a high density residential development proposed for the former Greenridge Country Club golf course. Stormwater runoff from this area will enter the Alpine-Walker Drain. Since the drain is probably the most fragile area of the stream system, any developments that contribute additional water to it are to be considered critical areas, regardless of location. It is important for local units of government to keep the stated goals of this plan in mind when reviewing proposed developments, particularly those in critical areas.
AWRI compiled or generated additional information that was not relied on for determination of critical areas, but might be used by local planners in making land use decisions. An example of this is information on prime farmland soils (Figure 20). This information might be compared with current land use, allowing local officials and township residents to determine those areas that are best suited for their current use, and those areas which might be better candidates for land use changes.
Figure 17. Flooding Frequency - York Creek Watershed
Figure 18. Sheet and Rill Erosion Potential - York Creek Watershed
Figure 19. Critical Areas - York Creek Watershed
Figure 20. Prime Farmland Soils - York Creek Watershed
Page last modified January 19, 2011