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Applications of LIDAR Data in the McPherson Watershed, Fort Bragg, North

Carolina 

Beth M. Wrege and Michelle CienekU.S. Geological Survey

Raleigh, N.C.

The U.S. Geological Survey (USGS) is working with Fort Bragg, N.C., in the development of a Stormwater Pollution Prevention Plan and with the development of a watershed-management plan. This effort will enable Fort Bragg to develop best management practices for reducing surface-water pollutants in the Little and Cape Fear Rivers. Eight subwatersheds intercept Fort Bragg’s cantonment area, including the McPherson watershed. The cantonment area quarters the majority of the troops stationed at Fort Bragg and contains the majority of the Base’s industrial activities and is therefore an area of potential high stormwater pollution impact. Approximately 603 acres, or 15 percent of the 4,026 acres (6.29 square miles) in the McPherson watershed, drain the cantonment area.

In order to develop best management practices and effectively manage their watersheds, Fort Bragg must have information on surface elevation, drainage basins, stormwater-conveyance systems, streamflow, and current manmade and natural features within the watersheds. Once relevant data sets are obtained and compiled in a digital format within a Geographical Information System, they can provide a base from which to address watershed-management questions. To analyze these data efficiently and accurately, the data need to be translated into a scale that reflects the detail necessary to interpret hydrologic conditions within small watersheds.

The highest resolution continuous-surface elevation data set currently available for Fort Bragg is the USGS National Elevation Dataset. However, the resolution of 30-meters of this dataset proves is too coarse for working with watersheds at this scale. Existing vector elevation data also were considered for use within the GIS. The current highest resolution elevation contours available for Fort Bragg have a 2-foot contour interval but lack elevation tags and connectivity. These digital contours are applicable to engineering purposes but lack the needed portability for effective use in a GIS.

For this pilot study, to generate high resolution surface data, Light Interferometric Distance and Ranging (LIDAR) data were used. These data, which were collected in August 1998 by Earthdata, Inc., (1) were ortho-rectified and tagged at 5-meter intervals. A LIDAR-based surface-elevation map of the McPherson watershed was created as a pilot study for watershed assessment at Fort Bragg. The LIDAR point data were examined at 10-meter, 5-meter, 1-meter, and 2-foot interval resolutions, and the 5-meter interval was selected for use in the watershed analysis. Arc/Info (1) software was used to create a digital elevation model with a 5-meter cell size. The 5-meter data were used to create elevation contours, flow direction and flow accumulation grids, subbasin delineation, and a 3-D surface map.

The pilot study demonstrates one approach to subwatershed data management. These spatial data can be effectively used as part of Fort Bragg’s stormwater-management plan, or the watershed-management plan. The advantages obtained from using LIDAR in this study include a data set with digital elevations that allows for control of topographic intervals, control of map units, tagged topography, and overlay ability. The new elevation data layer can be combined with existing data sets to better define watersheds and calculate the effects of sedimentation and rainfall runoff. Model runs based on these data can be used to determine and target high-risk areas susceptible to surface-water runoff and erosion. In addition, the LIDAR data can be used to document topographic change within Fort Bragg.

Periodic surveys using LIDAR data can assist resource managers in understanding long-term resource trends and in estimating the effects of watershed-management efforts, erosion-control devices, and best management practices. The LIDAR data also can be used following a hurricane, a major storm event, or other significant event to effectively assess the storm’s impact and to measure erosion. The McPherson watershed pilot study demonstrates the feasibility for using LIDAR data for watershed analysis.

(1) The use of firm, trade, or brand names in this document is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Study Area Existing DataGIS and Data Layers

LIDAR

Comparison

Microstation DXF data are available in a readable format

The USGS has data in several scales: 1:250,000, 1:100,000, and 1:24,000 are readily available for the Fort Bragg Area

LimitationsThe LIDAR files are large

Data are preprocessed

Interval validity is limited

ApplicationsWatershed delineation

Stormwater mapping

Best Management Practice development

Overlay of data layers

SuggestionsTrack metadata

Existing data has ground-control

AdvantagesControl of topographic intervals

Control of units

Ease of change

Tagged topography

Data acquisition timing

Applications: LIDAR data can be used to delineate watersheds, create contours, and general resource management

Applications of LIDAR Data in the McPherson Watershed, Fort Bragg, North Carolina Beth M. Wrege and Michelle Cienek Water Resources Program USGS, Raleigh, NC

McPherson Creek Watershed• LIDAR is an acronym for Light Interferometric Distance and Ranging

•LIDAR data is collected by aerial topographic surveys that measure elevation using lasers.

• The first LIDAR lasers existed in the 1970’s but lacked applicability until the development of accurate Global Positioning System units, powerful and inexpensive computers and public availability of LIDAR systems.

•LIDAR is an active sensor that works by pulsing a laser pulse at a rate of 2,000 to 5,000 times per second. It measures each pulse’s return time to map surface features.

• The vertical precision of LIDAR data is stated to be +/- 6 inches of reality.

• LIDAR produces a point coverage with elevation for each point.

BenchmarkSurveyed

Elevation (m)LIDAR

Elevation (m)Difference

Elevation (m)

3-t-2-1 117.7000 117.2083 0.4917field 117.7168 118.1530 0.4362moon 104.7750 100.2962 4.4788cass 106.0948 104.6875 1.407363e 3-4 117.8367 117.9875 0.1508grub 111.6726 111.5019 0.1707bank 109.3165 109.7691 0.4526long 88.0903 87.5043 0.585963e 3-5 95.0359 95.0036 0.0323pratt 80.8147 78.2788 2.535963e 3-6 81.3146 80.1403 1.1743gorm 78.8731 78.9344 0.0613range24 85.5574 85.9650 0.4076bm "gun" 73.1490 73.3416 0.1926pope 59.1983 59.1511 0.0472water 51.8800 53.9290 2.0490bm fire 61.6245 61.8385 0.2140pts 15 mac 56.1116 54.2018 1.9097

0.9332Average Difference:

Comparison of Elevations in McPherson Watershed

Average Difference: ± 1 meter

• Applications of Advanced LIDAR for DEM Applications, Micheal S. Renslow, http://www.sbgmaps.com/lidar_apps.htm

• Inertial Measurement and LIDAR Meet Digital Ortho Photography: A Sensor Fusion Boon for GIS, Robert G. Kletzli and John L. Peterson

• http://www.arcdataonline.com/library/userconf/proc98/PROCEED/TO600/PAP597/P597.HTM

3-D View

Contours

Overlay

Watershed

Fort Bragg Cantonment Area