Appendix III Land Cover

Appendix III

Land Cover
in the
Roanoke River Basin
Appendix III – Land Cover 213

214 Appendix III – Land Cover

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 Roanoke 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
Roanoke 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 following chart
provides an illustration of the relative amount of land area that falls into each major cover type
for the Roanoke 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.

Appendix III – Land Cover 215

12 % Cultivated Crop
11 % Pasture/Managed
Herbaceous Land Cover
3 % Water
1% Urban/
Built-Up Areas
73 % Forest/Wetland
Percentages within Major Land Cover Categories in the Roanoke River Basin

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.

216 Appendix III – Land Cover

%
change
Acres Acres Acres Acres Acres Acres % of Acres % of since
LAND COVER (1000s) % (1000s) % (1000s) % (1000s) % (1000s) % (1000s) TOTAL (1000s) TOTAL 1982
Cult. Crop 81.6 14.7 58.1 12.2 22.1 11.3 21.0 13.1 198.2 24.3 381.0 17.3 478.7 21.6 -20.4
Uncult. Crop 29.3 5.3 10.1 2.1 2.1 1.1 5.5 3.4 0.0 0.0 47.0 2.1 24.8 1.1 89.5
Pasture 28.5 5.1 27.8 5.8 15.0 7.7 4.9 3.1 11.6 1.4 87.8 4.0 111.8 5.0 -21.5
Forest 318.5 57.2 329.8 69.3 110.9 56.7 90.6 56.4 520.3 63.8 1370.1 62.1 1377.4 62.1 -0.5
Urban & Built-Up 55.0 9.9 18.6 3.9 8.2 4.2 14.4 9.0 33.4 4.1 129.6 5.9 54.9 2.5 136.1
Federal 0.0 0.0 0.0 0.0 14.0 7.2 0.0 0.0 6.2 0.8 20.2 0.9 14.8 0.7 36.5
Other 43.9 7.9 31.4 6.6 23.4 12.0 24.2 15.1 46.3 5.7 169.2 7.7 154.2 7.0 9.7
Totals 556.8 100.0 475.8 100.0 195.7 100.0 160.6 100.0 816.0 100.0 2204.9 100.0 2216.6 100.0
% of Total Basin 25.3 21.6 8.9 7.3 37.0 100.0
SUBBASINS 03-02-01 03-02-02 03-02-03 03-02-04 03-02-08 03-02-09
03-02-05 03-02-06
8-Digit
Hydraulic Units
Source: USDA, Soil Conservation Service - 1982 and 1997 NRI
* = Watershed areas as defined by the 8-Digit Hydraulic Units do not necessarily coincide with subbasin titles used by DWQ.
03010103 03010104 03010106 03010107
Upper Dan Lower Dan Middle Roanoke
MAJOR WATERSHED AREAS
Roanoke Rapids Lower Roanoke
1997 TOTALSRiver 1982 TOTALSRiverRiverRiverRiver
03-02-03
03-02-07
03-02-08 03-02-10
03-02-06

03010102

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
Appendix III – Land Cover 217
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 74,700 acres. Uncultivated croplands increased by
22,200 acres while cultivated cropland decreased by 97,700 acres. Forest and pastureland cover
significantly decreased by 7,000 and 24,000 acres, respectively. Most land cover change is
accounted for in the Lower Roanoke River hydrologic unit that includes rapidly growing areas in
Warren County. Below is a graph that presents changes in land cover between 1982 and 1997.

Source: USDA-NRCS, NRI, updated June 2001
Land Cover Type
Cult. Crop Uncult. Crop Pasture Forest Urban & Built-up Federal Other
La
n
d

C
o
v
e
r

C
h
a
n
g
e

(
%
)
-40
-20
0
20
40
60
80
100
120
140
160
-20.4
89.5
-21.5
-0.5
136.1
36.5
9.7
218 Appendix III – Land Cover