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Assignment #4 There is no link
to these files, due to a space issue.
Final Project:
Concentration of
Surface Nitrates in Aquifer Recharging Cave Systems
My final project
looks at defining watersheds that collect Cattle manure during flashflood
events and deposit it in sink holes that recharge local aquifers.
During my
exploration and mapping of caves in central
Is manure from ranching in the karst region of central
When is manure on
range land a problem to aquifer contamination?
When it becomes concentrated and nitrates are injected directly into
the aquifer.
This happens on arid range land where cow pies do not break down
(long residence time).
Then heavy precipitation
events float cow pies to arroyos.
The arroyos drain into sinkholes in Karst
topography.
The sinkholes are drained by cave system which recharges aquifer.
Nitrates leach from cow pies in the cave and contaminate the
aquifer.
GIS WORK:
Objective:
Calculate the amount of manure being transported into a specific cave.
Phase 1is to determine
the area of drainage basin that feeds manure into a specific cave system. This
is what this GIS project is about. See the future work section of this web site
for what’s next. The first thing I had to do was determine my study area ( Figure 1& 2)
Figure 1: Study
area in central
Figure 2: Close-up
of study area and area of interest
Step 1 of
calculating drainage basin area,
Get DEM of study area.
Figure 3: DEM of
my study area.
Step2:
Create flow direction map. (Figure 3)
I overlaid the flow direction grid with a
stream grid.
I chose NOT to
“burn in” or fill spurious pits in the DEM because many of the drainage basins
are closed basins in a low relief topographic setting.
Figure 3: Flow
directions in area of interest.
I overlaid an air
photo with my stream network to check for accuracy, it seems to match fairly
well. The air photo was georeferenced against the road network(Figure
4).
Figure 4:
Step 3:
Create drainage basins (Figure 5)
Sink holes with cave systems have also been
added.
Figure 5: Drainage
basins have been created and the stream network and caves have been overlaid.
Seeing which
drainage basins are connected to a cave system I can figure out which basins are contributing manure to a cave system.
Step 4
Calculate area of
drainage basins flowing into cave system. I selected the contributing drainage
basins and used a VBA script to calculate the area of each basin. There were 7
contributing basins. See Figure 6
.78 sq miles
.26
.72
.61
.23
.06
.02
----------------
2.68 sq miles
Drained into cave
system
Figure 6: Here are
the selected drainage basins with their areas.
Future work
Calculate cow pies per sq mile
Volume of manure per sq mile
Percentage of cow pies entering cave system
Volume of manure entering cave system
Amount of nitrate entering aquifer
Data sources:
RGIS – data
USGS seamless –
DEM
ESRI, arcscripts, VBA script author-Guoyun
Zhou
