An Evaluation of Forested
Buffers in the Murderkill Watershed

By Mike Krumrine, Environmental Scientist

Tributary Action Team (TAT) members for the Murderkill Watershed are currently working with DNREC to develop Pollution Control Strategies to decrease nutrient loading in the Murderkill Watershed as part of their effort to meet the Total Maximum Daily Load (TMDL) requirements and to improve and protect the water quality in the watershed.  One recommendation advocated by the team is the implementation of forested riparian buffers.  These buffers are small strips of permanently forested land adjacent to streams, lakes, or wetlands providing a transition zone between the water resource and human land use.  They offer multiple benefits including improved water quality, flood control, erosion reduction, and increased bank stabilization.  To assist the team, DNREC conducted an analysis of the current status of forested riparian buffers along waterways within the watershed using Geographic Information Systems (GIS) software.

Stream reaches in the Murderkill Watershed that either lack forested riparian buffers, or have only narrow forested riparian buffers were identified using ESRI’s ArcGIS software.  The analysis included the use of multiple layers of data including 1997 forest cover data from the Delaware Natural Heritage and Endangered Species Program, hydrography data from the U.S. Geological Survey (USGS), 2002 wetlands maps from the Delaware Statewide Wetlands Mapping Project (SWMP), and public lands data from DNREC’s 2004 Outdoor Resources Inventory (ORI).  Since the forest cover data was somewhat outdated, 2002 aerial photos were also used to help update some of the data as needed.

The GIS software was used to identify 100 foot buffer areas around rivers, streams, and tax ditches, and 50 foot buffer areas around freshwater wetlands (Figure 1).  Tidal wetland areas were considered unsuitable for the establishment of forested buffers and were removed from the analysis.  Tidal portions of the river and any tidal tributaries were included in the analysis.   Buffers around tidal areas were considered adequate if the wetlands extended at least 100 feet from the edge of the water.   For non-tidal areas, buffers were considered adequate if the entire designated buffer areas consisted of forested lands.   Stream sections within the watershed were categorized into three groups according to the status of the adjacent forested riparian buffers:

1. 1) adequate forested buffers along both stream banks
2. 2) deficient forested buffers along either one or both stream banks
3. 3) no forested buffers along either stream bank.

Since the establishment of additional forested riparian buffers has a greater likelihood of being implemented on public lands than on privately owned lands the analysis was broken out for both publicly owned and private lands.

Within the Murderkill Watershed there are approximately 230 miles of waterways excluding ponds and reservoirs.  The study found that out of 230 miles of rivers, streams, and tax ditches, only 130 miles (57%) are adequately buffered along both stream banks.   67 miles (29%) have deficient buffers along either one or both of the stream banks, and 33 miles (14%) have no stream buffers along either stream bank (Figure 1).

Figure 1 (Download the 2.3 MB PDF version or the 1.0 MB SWF version for greater detail.)

Within the Murderkill Watershed only 26 miles (11%) of rivers, streams, and tax ditches flow through publicly owned lands.  Waterways in public ownership fared much better than those in privately owned lands.  Within public lands, 21 miles (81%) are adequately buffered along both stream banks, 4 miles (15%) have deficient buffers along either one or both of the stream banks, and only 1 mile (4%) had no forested buffer along either stream bank (Figure 2).

Figure 2 (Download the 2.2 MB PDF version or the 1.0 MB SWF version for greater detail.)

Overall, most of the tidal portions of the watershed and the main stem of the Murderkill River are adequately buffered.  The areas in most need of attention are the agricultural tax ditches, many of which have no forested riparian buffers.  The analysis also emphasizes the importance of working in cooperation with private landowners, since a majority of the waterways flow through privately owned lands.  43% of the waterways within the Murderkill Watershed are not adequately protected by forested riparian buffers that are capable of reducing the loading of excess nutrients and sediment.