Riparian Buffers: Percent Forested, Percent Under Conservation Management
What is this?
Riparian buffers are lands adjacent to streams where vegetation is strongly influenced by the presence of water. This indicator reports the percentage of the riparian buffer zone (30 meters (98 feet) on each side of stream) that is forested for each county and the entire Triangle region. The percentage of riparian buffers that are managed for conservation and open space is also reported.
Why is this important?
Riparian buffers serve a crucial role in maintaining good water quality. Buffers help prevent sediment, nitrogen, phosphorous, pesticides and other pollutants in storm water runoff from reaching a stream. The woody debris and leaf litter produced by vegetative buffers also provide a major source of energy and nutrients for in-stream communities. Overhanging vegetation helps keep streams cool, which can be very important for cold-water fish species such as trout.
Heavily vegetated buffers help maintain stable stream banks and protect downstream property from flooding. Buffers allow groundwater to be recharged and sedimentation to be deposited building stream banks. When buffers are degraded by reducing or removing vegetation there are many consequences. In addition to altered wildlife and fish populations, property damage from flooding and erosion, loss of valuable agricultural lands, and increased water temperatures, degraded buffers can cause increased sedimentation, decreased dissolved oxygen, and cause significant reductions in aquatic stream life.
Riparian buffers are the zone of vegetation adjacent to streams, rivers, creeks or wetlands where vegetation is strongly influenced by the presence of water. They are also called vegetated buffer zones and are evidence of wise land use management (best management practices). photo source: http://www.epa.gov/nrmrl/pubs/600R05118/600R05118.pdf
What does this measure show?
Chatham, Lee, and Orange County have the highest percentages of forested riparian buffer and all three are above the Triangle average (Figure 1). Wake County has the lowest percentage of forested buffer, only 62%. The Triangle region as a whole has 68% of riparian buffers in forest cover.
In the Triangle, 11.6% of riparian buffers are protected in land which is managed for conservation and open space purposes.
The Neuse River Basin Rules require 50-foot riparian buffers. Ideally, the region should be striving for completely forested buffers. Figure 1. This graph represents the percentage of the total area within the riparian buffer zone (30 m on either side of a stream) that is forested.
Limitations & Further Research
The biggest limitation with this analysis is that the land cover layer we used has a resolution of 30 meters (approximately 100 feet); finer resolution data for the entire Triangle are not available. Many agencies and governments have buffer requirements smaller than 100 feet, but the resolution of the land cover layer prohibits an analysis at a finer scale. The National Land Cover Dataset is not able to distinguish between forested with understory intact and tree cover. The degree of forestation may not directly correspond to the quality of buffer.
When the 2006 National Land Cover Dataset is available, this indicator should be calculated again, to make a comparison between 2001 and 2006. There is currently a layer available for 1992, but direct comparisons are not recommended because they were mapped with different methods and slightly different classifications.
Author Ginevra Ryman, Duke University :: 2010 April 23 Reviewers Tom Davis, Water Resources Coordinator, Orange County :: Amy Pickle, Duke University Technical Notes
Where the data came from: Land cover data was from the National Land Cover 2001 Dataset (Homer et al. 2004). Stream data was from the Statewide 24K hydrography layer from NC OneMap . Lands managed for conservation and open space were from NC OneMap .
How measured: The total area of riparian buffer was divided by the total area of forested riparian buffer, to give the percent covered in forest. This was done for each county, and the entire Triangle region.
Analyses performed: All geographic information system layers were clipped to the six county Triangle region. Buffers were created using the ‘Buffer’ tool, with a distance of 30 meters, side type = full, end type = round, dissolve = all. The result was converted to a raster with resolution 30m. The land cover was reclassified so that deciduous forest, evergreen forest, mixed forest, woody wetlands, and herbaceous wetlands were considered ‘forested.’ The forested layer was then extracted by the buffer, and the percentage of forested buffer was calculated for each county, and the entire region.
Fresh Water Supply :: Water Use
Water Pollution :: Miles of Impaired Streams :: Riparian Buffers :: Major Dischargers :: Groundwater
Case Studies :: Jordan Lake Rules :: Falls Lake Rules
Riparian Buffers: Percent Forested, Percent Under Conservation Management
Riparian buffers are lands adjacent to streams where vegetation is strongly influenced by the presence of water. This indicator reports the percentage of the riparian buffer zone (30 meters (98 feet) on each side of stream) that is forested for each county and the entire Triangle region. The percentage of riparian buffers that are managed for conservation and open space is also reported.
Why is this important?
Riparian buffers serve a crucial role in maintaining good water quality. Buffers help prevent sediment, nitrogen, phosphorous, pesticides and other pollutants in storm water runoff from reaching a stream. The woody debris and leaf litter produced by vegetative buffers also provide a major source of energy and nutrients for in-stream communities. Overhanging vegetation helps keep streams cool, which can be very important for cold-water fish species such as trout.
Heavily vegetated buffers help maintain stable stream banks and protect downstream property from flooding. Buffers allow groundwater to be recharged and sedimentation to be deposited building stream banks. When buffers are degraded by reducing or removing vegetation there are many consequences. In addition to altered wildlife and fish populations, property damage from flooding and erosion, loss of valuable agricultural lands, and increased water temperatures, degraded buffers can cause increased sedimentation, decreased dissolved oxygen, and cause significant reductions in aquatic stream life.
The trees form a riparian buffer along both sides of this stream.
photo source: http://www.nrcs.usda.gov/NEWS/images/iabufferlarge.jpg
Riparian buffers are the zone of vegetation adjacent to streams, rivers, creeks or wetlands where vegetation is strongly influenced by the presence of water. They are also called vegetated buffer zones and are evidence of wise land use management (best management practices).
photo source: http://www.epa.gov/nrmrl/pubs/600R05118/600R05118.pdf
What does this measure show?
Chatham, Lee, and Orange County have the highest percentages of forested riparian buffer and all three are above the Triangle average (Figure 1). Wake County has the lowest percentage of forested buffer, only 62%. The Triangle region as a whole has 68% of riparian buffers in forest cover.
In the Triangle, 11.6% of riparian buffers are protected in land which is managed for conservation and open space purposes.
The Neuse River Basin Rules require 50-foot riparian buffers. Ideally, the region should be striving for completely forested buffers.
Figure 1. This graph represents the percentage of the total area within the riparian buffer zone (30 m on either side of a stream) that is forested.
Limitations & Further Research
The biggest limitation with this analysis is that the land cover layer we used has a resolution of 30 meters (approximately 100 feet); finer resolution data for the entire Triangle are not available. Many agencies and governments have buffer requirements smaller than 100 feet, but the resolution of the land cover layer prohibits an analysis at a finer scale. The National Land Cover Dataset is not able to distinguish between forested with understory intact and tree cover. The degree of forestation may not directly correspond to the quality of buffer.
When the 2006 National Land Cover Dataset is available, this indicator should be calculated again, to make a comparison between 2001 and 2006. There is currently a layer available for 1992, but direct comparisons are not recommended because they were mapped with different methods and slightly different classifications.
Author Ginevra Ryman, Duke University :: 2010 April 23
Reviewers Tom Davis, Water Resources Coordinator, Orange County :: Amy Pickle, Duke University
Technical Notes
Where the data came from: Land cover data was from the National Land Cover 2001 Dataset (Homer et al. 2004). Stream data was from the Statewide 24K hydrography layer from NC OneMap . Lands managed for conservation and open space were from NC OneMap .
How measured: The total area of riparian buffer was divided by the total area of forested riparian buffer, to give the percent covered in forest. This was done for each county, and the entire Triangle region.
Analyses performed: All geographic information system layers were clipped to the six county Triangle region. Buffers were created using the ‘Buffer’ tool, with a distance of 30 meters, side type = full, end type = round, dissolve = all. The result was converted to a raster with resolution 30m. The land cover was reclassified so that deciduous forest, evergreen forest, mixed forest, woody wetlands, and herbaceous wetlands were considered ‘forested.’ The forested layer was then extracted by the buffer, and the percentage of forested buffer was calculated for each county, and the entire region.
References
Homer, C. C. Huang, L. Yang, B. Wylie and M. Coan. 2004. Development of a 2001 National Landcover Database for the United States. Photogrammetric Engineering and Remote Sensing, Vol. 70, No. 7, July 2004, pp. 829-840.
North Carolina Center for Geographic Information and Analysis, 20060210, Statewide 24K hydrography (polys): North Carolina Center for Geographic Information and Analysis, Raleigh, NC .
NC Center for Geographic Information and Analysis, 20020228, onemap_prod.SDEADMIN.lmcos: NC Center for Geographic Information and Analysis, Raleigh, North Carolina .
Neuse River Buffer Rules: 15A NCAC 02B .0233 NEUSE RIVER BASIN: NUTRIENT SENSITIVE WATERS MANAGEMENT STRATEGY: PROTECTION AND MAINTENANCE OF EXISTING RIPARIAN BUFFERS
http://reports.oah.state.nc.us/ncac/title%2015a%20-%20environment%20and%20natural%20resources/chapter%2002%20-%20environmental%20management/subchapter%20b/15a%20ncac%2002b%20.0233.html
Water Indicators
Fresh Water Supply :: Water Use
Water Pollution :: Miles of Impaired Streams :: Riparian Buffers :: Major Dischargers :: Groundwater
Case Studies :: Jordan Lake Rules :: Falls Lake Rules