Hydrologic Modeling, Vegetative Mapping & Runoff Management
1. Hydrologic Modeling
drainage patterns, categorize its stream segments and delineate its component sub basins.
First we must fill the DEM.
After filling in the given DEM with all of the local depressions filled in, we can identify the flow direction for each cell
Below is the Flow Direction Map.
Then we used the Basin tool on this flow direction map and created a map that gave each watershed a unique value.
The map can be seen below with the largest basin (The Nanticoke) outlined.
The next step was to use the flow accumulation tool to find the drainage paths, those can be seen in the map below.
Using this drainage path raster, we can identify the inferred streams, i.e. all of the cells that exceed a flow accumulation
threshold value of 15,000.
We then used the streamlink tool to create a network of streams that can be seen below.
Then we created a vector polyline layer of the stream links that can be seen below.
We then find the sub basin areas that drain into each of the identified streams in the network found above.
The Flow Accumulation tool can be used, as seen above, to find the drainage paths. However, we can also use a weight
map with flow accumulation to calculate accumulations of specific category cells, such as agricultural cells in the inferred stream
cells only. We first create a weighted map and then re-run the flow accumulation tool with this weighted map.
The weighted map can be seen below, and specifies cells where the land use is equal to 81 and 82.
The weigthed flow accumulation map can be seen below.
Next, we can calculate the percentage of runoff that originates from the agricultural cells in the inferred stream
cells only, this raster can be seen below.
To obtain a clearer visualization of the relative vulnerabilities of stream segments to agricultural runoff,
we can identify the cells with maximum values using a 5x5 neighborhood. This result can be seen below.
Using the satalite Landstat image that includes three layers, a Near-Infared layer, a Red layer and a Green layer,
we will create a Normalized Difference Vegitation Index. Calculating this raster, we need to use the standard NDVI formula.
(Near-Infared - RED)/(Near-Infared + RED)
Since vegitation absorbs visible Red and reflects Near Infared, this formula will provide a useful index of biomass
density, or our Normalized Difference Vegitation Index as can be seen below, the black areas of the graph represent no
vegitation and the areas with high vegitation are displayed in green.
We can then identify the open water features by isolating the cells in the Near-Infared layer that have a value less then
or equal to 120. Below is a map of all of the open water features.
Then to eliminate the stray cells or ponds, and isolate the Nanitoke River system itself, we use the Region Group tool
that will clump together cells that have neighboring cells, giving us just the Nanitoke River system that can be seen below.
This portion of the project identifies the appropriate stream protection buffers needed around the Nanitoke River system.
We will use weighted distance algorithms to create cost distance maps that we will use to establish our buffer zones.
First we must establish a buffer on the river system where vegitation is not dense. Areas with dense vegitation will intercept
much more runoff then those with little vegitation. To establish a buffer we must first create the cost distance map for the NDVI.
Next we need to establish a buffer on the river system considering the slope of the land. The steeper the slope of the land
the more susceptible it is to runoff. To establish a buffer we must first create the cost distance map for the slope.
Using these two cost distance maps, we can create a buffer map for the Nanitoke River system.
Below is a closeup of the vegitation buffer (buffer highlighted in red) to show how it is focused in areas with a low density of vegitation.
Below is the map of both buffers, with the slope buffer highlighted in purple, the vegitation buffer highlighted in
green, and areas with both buffers highlighted in red.
The Nanticoke River system is approximately 50 miles long and has the largest watershed in Delaware. This watershed
occupies about one-third of Delaware's land surface.This being said, it is a very important watershed to the ecosystem
of Delaware, its area of interconnected uplands, wetland and waters providing home to over 250 endangered plant and
animal species. This watershed has been a focus for protection mainly for the issues it is facing as well as its
abundance of rare fauna and flora along with its many other unique biological communities.
Approximately 43% of the land in the Nanticoke watershed is used for agriculture, such as animal production farms.
These animal production farms not only lead to pollutants in the water system but also the developed land has affected
the runoff experienced by the watershed. The developing urban areas in the Nanticoke watershed region have also
caused runoff. Development of this land has taken away vegetation that has intercepted runoff in the pass, causing a
raising issue for the watershed.
To protect the river, the state of Delaware has designated the Nanticoke River System as an “Exceptional Recreational
and Ecological Resource”, or ERES. With this designation, comes a commitment by the state of Delaware to increase
the treatment of incoming wastewater. The main focus for this process is the animal production farms, and educating
urban areas about proper septic system maintenance.
There is also in place, a Nanticoke Watershed Alliance. This alliance has representatives from industry, agriculture,
environmental, business, community, state, local and federal government organizations, all working together to protect
the Nanticoke watershed. One of their main programs is the development of agricultural buffers. This includes working
with farmers to plant flexible-width buffer strips of native grasses along their drainage ditches. The alliance also
performs water quality assessment throughout the year by collecting bi-weekly samples at six different sites. Monitoring
these and ensuring that they are meeting protocol is an essential way to improve life for the affected ecosystems.
After performing this analysis, there are some suggestions I could make to ensure that the Nanticoke river system does
not incur any further damage as well as improves in quality. First I would suggest a restriction on extensive further land
development, as well as an incentive program for land donation to the watershed alliance or the state of Delaware. This
will stop the watershed area from further development and loss of agriculture and hopefully slowly expand available
vegetative land available. Another suggestion is to put an emphasis on educating urban areas about monitoring their
contribution to the pollution in the area. While laws put in place can control the corporations, the surrounding urban
areas cannot be put on such restrictions. However, education is the best gateway to improving an issue among an urban
setting. The current monitoring done by the Nanticoke Watershed Alliance is a good tool in the maintenance of the
Nanticoke river system, but this strategy focuses more on targeting the sources of the problems.
The main cost of this strategy would be from the land incentives. I would propose that the state of Delaware apply for
an environmental conservation grant from the federal government to use for this purpose of the strategy. Educating the
urban areas about their impact on the watershed region and how to lessen it will have minimal costs and fundraising
done by various organizations such as the Nanticoke Watershed Alliance can cover those minimal costs.
Smithsonian Environmental Research Center
Nanticoke Restoration Work Group Restoration Plan 2012
Nanticoke Watershed Alliance
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