Brian Krasnoff HW 2
Part 1
According to the USGS the location for the Raritan River at Manville, NJ station is at
approximately 40.556 °N 74.58° W. And the reported drainage area is 490 square miles.
Using Digital Elevation Models accessed through the USGS’s National Map, I delineated the
watershed as seen below. The green point is the outlet which corresponds to the station at
the Raritan River in Manville, NJ. The area of this delineated watershed of 492 square miles
was found by using ArcGIS’s Define Projection tool, I was able to convert the polygon to the
Alber’s Equal Area Conic coordinate system so that the listed area on ArcGIS would be in
m^2 which is easily converted to mi^2.
USGS’s listed drainage area of 490 square miles and the area of the delineated watershed
of 492 square miles are extremely close to each other. This verifies that the delineated
watershed is very accurate and the slight discrepancy between the two values is either a
product of using not very precise data or by a slight variation in the outlet of the delineated
watershed from the actual station.
Part 2:
The 5 points I selected to use to find the average precipitation for the watershed are labeled
on this map.
1
2
3
4
5
After collecting the daily average precipitation at these 5 locations, I used ArcGIS’s Create
Thiessen Polygon tool to divide the shape into 5 polygons which will be used to calculate
the average.
Based on the weighted average gotten through the Thiessen Polygon method, I compiled
the data for Hydrologic year 2023 and 2024 and plotted them both together and separately
to easily compare the two years daily precipitation depth.
Average Daily Precipitation in HY2023 and
HY2024 (mm/day)
100
80
60
40
20
0
Average 2024 prcp (mm/day)
Average Daily Precipitation in
HY2023 (mm/day)
Average Daily Precipitation in
HY2024 (mm/day)
Cummalitve Precipatation (mm)
1600
1400
1200
1000
800
600
400
200
0
Cumulative 2023 prcp (mm/day)
Cumulative 2024 prcp (mm/day)
Comparing the twos as a whole, they totaled almost the exact same amount of
precipitation, approximately 1.4 meters. The biggest differences were when the biggest
1-Sep
1-Aug
1-Jul
1-Jun
1-May
1-Apr
1-Mar
1-Feb
1-Jan
1-Dec
90
80
70
60
50
40
30
20
10
0
1-Oct
1-Sep
1-Aug
1-Jul
1-Jun
1-May
1-Apr
1-Mar
1-Feb
1-Jan
1-Dec
1-Nov
1-Oct
90
80
70
60
50
40
30
20
10
0
1-Nov
Average 2023 prcp (mm/day)
storms occurred in each year. In HY2024, the biggest storms occurred in between late
November and early January. But in HY2023, there were less very large storms overall but
the biggest occurred between late June and early July.
Part 3:
The data was collected through NASA's Oak Ridge National Laboratory Distributed Active
Archive Center DAYMET system. To estimate the PET, I used the Hamon’s Equation as it was
the method that the DAYMET’s system had all of the required components to calculate. And
to average daily temperature, I simply took the arithmetic mean of the recorded maximum
temperature and the recorded minimum temperature.
mm/month
PET and Percipation by Month in mm in
HY2024
300
250
200
150
100
50
0
Months
PET(mm/month)
Precipitation(mm/month)
Between the months of November and April and in August, there was more precipitation
than PET which means there was a water surplus. This means that overall there is more
water entering the system than leaving so there will be a net groundwater recharge and
surface water storage will increase. In October, May and June, PET and Precipitation was
approximately equal. And only in July and September was there a water deficit, PET being
greater than Precipitation. This water deficit means that the atmosphere wants to take
more water from the ground than is coming in, so the soil will start to dry up.