Development of an Index to Prioritize Riparian Buffer Restoration 
Efforts in the Cooks Creek Watershed,
Pennsylvania

 

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Introduction

Cooks Creek Watershed is approximately 34-square miles in size.  It is located in Upper Bucks County, Pennsylvania.  The land use/land cover within the watershed is dominated by agriculture and deciduous forest.  Recently however, there has been a marked increased in residential development within the watershed.  Cooks Creek is a 4th-order stream and is designated as a ˇ°Class Aˇ± Wild Trout Stream by the Pennsylvania Fish and Boat Commission.

     View of Cattle Ranch within the Cooks Creek Watershed

The project was sponsored by the Bucks County Chapter of Trout Unlimited and funded by the PA-DEP Growing Greener Program.  The objectives of the project were to evaluate riparian corridor integrity, identify land parcels with degraded riparian buffers, prioritize ˇ°degradedˇ± riparian land parcels, and engage priority landowners in conservation and restoration efforts.  The riparian buffer restoration portion of the project was part of a larger effort that included 600 feet of stream restoration and the implementation of an environmental education curriculum with a nearby high school.

 

Riparian Restoration Prioritization Index

 

The riparian restoration prioritization index provides the basis for the priority ranking of each parcel.   There are 400 riparian parcels in the Cooks Creek Watershed.  Of those 400 riparian parcels, 161 parcels are 600 feet or longer in length.   By looking at these 161 parcels, 80 percent of the riparian area was covered.  The 161 parcels were narrowed down to those parcels with less than 75 feet of natural vegetation buffer.  The remaining parcels will be evaluated according to the riparian restoration prioritization index.  The riparian restoration prioritization index is as follows:

     GIS Delineation of Drainage Areas to Riparian Buffers 
     within Selected Land Parcels

 

Riparian Restoration Prioritization Index (RRPI)

(1-(BW/(BW+8)) * (1/(SO * 10)) * LUR * DA

SO = Stream Order

Stream order was considered due to its importance to water quality.  Stream order was determined by visual inspection of USGS 7.5 minute quadrangle maps. The degradation of streambanks or leaching of pollutants from overland runoff within first order drainages is assumed to be more damaging to water quality than similar processes occurring along a fourth order stream.  Therefore, first order streams were given higher sub index scores than higher order streams. The value of each stream order used in the RRPI is as follows:

 

  • First Order                   = 10.00
  • Second Order             =   5.00
  • Third Order                  =   3.33
  • Fourth Order                =   2.50

LUR = Land Use Rank

The land use ranking is based on total phosphorus loading rates of different land uses.  The land use was chosen based on the dominant land use in the drainage area.  These loading rates were chosen from unit area phosphorus loadings summarized by Reckhow et al., 1980. The ranking are as follows:

 

       Aerial Photograph Showing a Land Parcel with a 
       Denuded Riparian Buffer

Rank              Land Use                                 Total Phosphorus Loading

1.                        Low-Density Residential               0.19 kg/ha/yr

2.                        Pasture                                           0.25 kg/ha/yr

3.                        Industrial                                        0.75 kg/ha/yr

4.                        High-Density Residential              0.83 kg/ha/yr

5.                        Commercial                                    1.18 kg/ha/yr

6.                        Crops                                             2.24 kg/ha/yr

DA = Drainage Area

The drainage area is the area draining to a particular stream segment.  Drainage area was determined by delineating the drainage areas from a USGS topographic map in ArcView.  The area of each drainage unit was calculated using MILA Utilities in ArcView.  The area was then converted to square miles for the index.  This variable is combined in the index with land use rank.  This is intended to be a measure of the pollutant load reaching the stream.

BW = Buffer Width

Buffer width is a critical factor in determining the need for restoration at each parcel due to the pollutant removal potential of riparian buffers. Wider buffers provide more sediment and nutrient removal capability than narrow buffers, but the marginal value of a buffer decreases with increasing buffer width.