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Geographic Information Systems

Tanyard Branch Watershed Assessment

The Tanyard Branch, located in Easton, Talbot County, MD is a small watershed that drains into the Tred Avon River.

The Center for Environment and Society (CES) and the GIS Program at Washington College, in partnership with the Midshore Riverkeeper Conservancy (MRC) and Aloft Aerial Photography, conducted an assessment of this watershed for agricultural BMP implementation opportunities, which include assessments of urban neighborhoods, upland and developed areas, stream corridors, and a mix of commercial and publicly owned properties for stormwater management. The primary goals of this project were to understand the nature of the water quality issues for the watershed and to design and implement an improvement plan for water quality. The following webpage contains a bevy of products that mark the beginning of this project including aerial video, GIS analysis and an interactive online map of the watershed.

Our data is also available at ArcGIS Online.

Tanyard Watershed


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Deliverables

Figure 1: Watershed Boundary
This map shows the outline of the watershed boundary which is calculated to contain 910.78 acres.

Figure 2: Digital Elevation Model (DEM)
To complete this analysis we utilized the 1/9 Arc Second DEM USGS (3 meter resolution) data clipped to the Tanyard Watershed Boundary. The vertical accuracy of this data is +/- 8 inches and is a derivative product of the LIDAR data acquired by the Maryland Department of Natural Resources. The low elevation was 0.05 meters and the highest point was 24.55 meters

Figure 3: Watershed Delineation
Using the GIS data from DEM found in Figure 2, this data was then converted to a flow length map using ArcMap tools. By examining the hydrologic flow lines from the origination point we traced the outline of the watershed boundary. To assist in the delineation of this analysis the Tanyard Stormwater System was added to this map so it could be seen where manmade stormwater lines impacted the natural flow of water. The boundary was adjusted accordingly.

Figure 4: Tree Canopy
This layer was digitized by a using a visual assessment of aerial imagery from several sources such as county imagery from 2004 and 2008, and Near IR imagery from USDA NAIP, along with multispectral imagery from Digital Globe WorldView II. The tree canopy coverage attributed to be one of three types: deciduous, evergreen or mixed. Once the digitizing was complete, the data was clipped to the Tanyard Branch Watershed Boundary; then each type of canopy coverage was analyzed to determine acreage and percentage of watershed covered.

Figure 5: Impervious Surface
The impervious surfaces layer was digitized using a visual assessment of the aerial imagery, and was classified into eight separate categories. Once the digitizing was complete, the data was clipped to the Tanyard Branch Watershed Boundary; then each type of impervious surface was analyzed to determine acreage and percentage of watershed covered.

Figure 6: Building Outlines
The Talbot County GIS Buildings data were clipped to the Tanyard Watershed Boundary. The data was then divided into three types: commercial, no building and residential. The building land cover was then analyzed by determining the amount of acres covered by each type of building and then using that statistic to determine the percentage of watershed those types of buildings covered.

Figure 7: Land Use – Parcels
Using GIS data obtained from Talbot County the parcels were classified into ten categories. The data was clipped to the Tanyard Branch Watershed Boundary and then each type of parcel was analyzed to determine acreage and percentage of watershed covered.

Figure 8: Land Use – Structures
Using the parcel data obtained from Talbot County as a base map the staff utilized the American Planning Association Land Based Classification Standard to classify each parcel for Activity, Function, Structure, Site, and Ownership. This map shows the structure analysis.

Figure 9: Aspect
To determine Aspect the staff utilized 1/9 Arc second DEM USGS (3 meter resolution) data clipped to the Tanyard Watershed Boundary. The DEM data was then converted to an aspect analysis using ArcMap tools.

Figure 10: Slope
To determine Slope the staff utilized 1/9 Arc second DEM USGS (3 meter resolution) data clipped to the Tanyard Watershed Boundary. The DEM data was then converted to a slope analysis using ArcMap tools.

Figure 11: Hillshade
To determine Hillshade the staff utilized 1/9 Arc second DEM USGS (3 meter resolution) data clipped to the Tanyard Watershed Boundary. The DEM data was then converted to a hillshade analysis using ArcMap tools.

Figure 12: Residential Grass Evaluation
Using Talbot County parcels as a base all residential parcels were identified. The each parcel was visually examined and rated by comparing the brightness of the grass by using leaf-off aerial imagery and also by using WorldView II multispectral imagery. When the area was attributed it received a “Green Factor” score which was a number from 0-3 that categorized the brightness of the grass from dull (0) to very bright (3). The data was then clipped to the Tanyard Branch Watershed Boundary; and the coverage of the green grass was analyzed to determine acreage and percentage of watershed covered.

Figure 13: Wetlands
This data was received from the Maryland Department of Natural Resources and was clipped to the watershed boundary.

Figure 14: Soil Type
Using the boundary of the watershed as an Area of Interest (AOI), the staff clipped the NRCS soils data from the NRCS web soil survey site. The various types and acreages of various soils were then determined.

Figure 15: Hydric Soils
Using the boundary of the watershed as an Area of Interest (AOI), the staff clipped the NRCS soils data from the NRCS web soil survey site. This map shows whether the soils are hydric, partially hydric, or not hydric.

Figure 16: Soil Drainage
Using the boundary of the watershed as an Area of Interest (AOI), the staff clipped the NRCS soils data from the NRCS web soil survey site.

Figure 17: Ponding Frequency
Using the boundary of the watershed as an Area of Interest (AOI), the staff clipped the NRCS soils data from the NRCS web soil survey site. This map shows the ponding frequency.

Figure 18: Runoff Potential
Using the boundary of the watershed as an Area of Interest (AOI), the staff clipped the NRCS soils data from the NRCS web soil survey site. This map shows the soil runoff potential.