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HomeMy WebLinkAboutAppendix III Land Cover Appendix III Land Cover in the French Broad River Basin Appendices Land Cover Land cover can be an important way to evaluate the effects of land use changes on water quality. Unfortunately, the tools and database to do this on a watershed scale are not yet available. The information below describes two different ways of presenting land cover in the French Broad River basin. Land cover information from the North Carolina Center for Geographic Information and Analysis (CGIA) is useful in providing a snapshot of land cover in the basin from 1993 to 1995. This information is also available in a GIS format so it can be manipulated to present amounts of the different land covers by subbasin or at the watershed scale. Land cover information from the National Resources Inventory (NRI) published by the Natural Resource Conservation Service (NRCS) is presented only at a larger scale (8-digit hydrologic unit), but the collection methods allow for between year comparisons. The two datasets cannot be compared to evaluate land cover data. This information is presented to provide a picture of the different land covers and some idea of change in land cover over time. In the future, it is hoped that land cover information like the GIS formatted dataset will be developed to make more meaningful assessments of the effects of land use changes on water quality. This dataset would also be useful in providing reliable and small-scale information on land cover changes that can be used in water quality monitoring, modeling and restoration efforts. Center for Geographic Information and Analysis (CGIA) Land Cover The North Carolina Corporate Geographic Database contains land cover information for the French Broad River basin based on satellite imagery from 1993-1995. CGIA developed 24 categories of statewide land cover information. For the purposes of this report, those categories have been condensed into five broader categories as described in the table below. The chart of the following page provides an illustration of the relative amount of land area that falls into each major cover type for the French Broad River basin. Land Cover Type Land Cover Description Urban Greater than 50 percent coverage by synthetic land cover (built-upon area) and municipal areas. Cultivated Cropland Areas that are covered by crops that are cultivated in a distinguishable pattern. Pasture/Managed Herbaceous Areas used for the production of grass and other forage crops and other managed areas such as golf courses and cemeteries. Also includes upland herbaceous areas not characteristic of riverine and estuarine environments. Forest/Wetland Includes salt and freshwater marshes, hardwood swamps, shrublands and all kinds of forested areas (such as needleleaf evergreens, deciduous hardwoods). Water Areas of open surface water, areas of exposed rock, and areas of sand or silt adjacent to tidal waters and lakes. A-III-1 1% Urban/Built-Up Areas 14% Pasture/Managed Herbaceous Land Cover 1% Cultivated Crop 1% Water 83% Forest/Wetland National Resources Inventory (NRI) Land Cover Trends Land cover information in this section is from the most current NRI, as developed by the NRCS (USDA-NRCS, June 2001). The NRI is a statistically based longitudinal survey that has been designed and implemented to assess conditions and trends of soil, water and related resources on the Nation’s nonfederal rural lands. The NRI provides results that are nationally and temporally consistent for four points in time -- 1982, 1987, 1992 and 1997. In general, NRI protocols and definitions remain fixed for each inventory year. However, part of the inventory process is that the previously recorded data are carefully reviewed as determinations are made for the new inventory year. For those cases where a protocol or definition needs to be modified, all historical data must be edited and reviewed on a point-by- point basis to make sure that data for all years are consistent and properly calibrated. The following excerpt from the Summary Report: 1997 National Resources Inventory provides guidance for use and interpretation of current NRI data: The 1997 NRI database has been designed for use in detecting significant changes in resource conditions relative to the years 1982, 1987, 1992 and 1997. All comparisons for two points in time should be made using the new 1997 NRI database. Comparisons made using data previously published for the 1982, 1987 or 1992 NRI may provide erroneous results because of changes in statistical estimation protocols, and because all data collected prior to 1997 were simultaneously reviewed (edited) as 1997 NRI data were collected. The following table summarizes acreage and percentage of land cover from the 1997 NRI for the major watersheds within the basin, as defined by the USGS 8-digit hydrologic units, and compares the coverages to 1982 land cover. Definitions of the different land cover types are also presented. A-III-2 MAJOR WATERSHED AREAS Upper French Pigeon Nolichucky % Broad River River River 1997 TOTALS 1982 TOTALS change Acres Acres Acres Acres % of Acres % of since LAND COVER (1000s) % (1000s) % (1000s) % (1000s)TOTAL (1000s) TOTAL 1982 Cult. Crop 36.8 3.5 1.6 0.5 0.0 0.0 38.4 2.1 61.9 3.4 -38.0 Uncult. Crop 13.3 1.3 3.5 1.0 2.0 0.5 18.8 1.0 34.5 1.9 -45.5 Pasture 148.6 14.1 39.6 11.2 29.0 7.3 217.2 12.0 235.2 13.0 -7.7 Forest 484.2 46.0 117.6 33.2 243.8 61.3 845.6 46.9 905.1 50.2 -6.6 Urban & Built-Up 141.6 13.5 30.6 8.6 23.4 5.9 195.6 10.8 105.6 5.9 85.2 Federal 184.1 17.5 152.7 43.1 79.5 20.0 416.3 23.1 401.2 22.2 3.8 Other 44.1 4.2 8.3 2.3 19.9 5.0 72.3 4.0 60.7 3.4 19.1 Totals 1052.7 100.0 353.9 100.0 397.6 100.0 1804.2 100.0 1804.2 100.0 % of Total Basin 58.3 19.6 22.0 100.0 SUBBASINS 04-03-01 04-03-02 04-03-05 04-03-06 04-03-03 04-03-04 04-03-07 8-Digit Hydraulic Units 06010105 06010106 06010108 * Watershed areas as defined by the 8-Digit Hydraulic Units do not necessarily coincide with subbasin titles used by DWQ. Source: USDA, Soil Conservation Service - 1982 and 1997 NRI Type Description Cultivated Cropland Harvestable crops including row crops, small-grain and hay crops, nursery and orchard crops, and other specialty crops. Uncultivated Cropland Summer fallow or other cropland not planted. Pastureland Includes land that has a vegetative cover of grasses, legumes and/or forbs, regardless of whether or not it is being grazed by livestock. Forestland At least 10 percent stocked (a canopy cover of leaves and branches of 25 percent or greater) by single-stemmed trees of any size which will be at least 4 meters at maturity, and land bearing evidence of natural regeneration of tree cover. The minimum area for classification of forestland is 1 acre, and the area must be at least 1,000 feet wide. Urban and Built-up Areas Includes airports, playgrounds with permanent structures, cemeteries, public administration sites, commercial sites, railroad yards, construction sites, residences, golf courses, sanitary landfills, industrial sites, sewage treatment plants, institutional sites, water control structure spillways and parking lots. Includes highways, railroads and other transportation facilities if surrounded by other urban and built-up areas. Tracts of less than 10 acres that are completely surrounded by urban and built-up lands. Other Rural Transportation: Consists of all highways, roads, railroads and associated rights- of-way outside urban and built-up areas; private roads to farmsteads; logging roads; and other private roads (but not field lanes). Small Water Areas: Waterbodies less than 40 acres; streams less than 0.5 mile wide. Census Water: Large waterbodies consisting of lakes and estuaries greater than 40 acres and rivers greater than 0.5 mile in width. Minor Land: Lands that do not fall into one of the other categories. Source: USDA, Soil Conservation Service - 1982 and 1997 NRI A-III-3 Data from 1982 are also provided for a comparison of change over 15 years. During this period, urban and built-up land cover increased by 90,000 acres. Uncultivated cropland and pastureland decreased by 34,000 acres. Forest and cultivated cropland cover significantly decreased by 60,000 and 24,000 acres, respectively. Most land cover change is accounted for in the Upper French Broad River hydrologic unit that includes rapidly growing areas in Buncombe and Henderson counties. Below is a graph that presents changes in land cover between 1982 and 1997. -38.0 -45.5 -7.7 -6.6 85.2 3.8 19.1 -80.0 -60.0 -40.0 -20.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0 Cult. Crop Uncult. Crop Pasture Forest Urban & Built-up Federal Other Land Cover Type La n d C o v e r C h a n g e s ( % ) Source: USDA-NRCS, NRI, updated June 2001 A-III-4