2. Drainage Basin:
● Choconut Lake Drainage Basin
located in Susquehanna County,
PA
● Area: 1313 Acres;
57.2 x 106 Square Feet
● The lake area is 36 acres
3.
4. Digital Elevation Model
● A DEM was created in
arcGIS from lidar points
● Highest Elevation is at the
top of the basin at 1830 ft
● Lowest Elevation is at the
bottom of the basin at 1230
ft.
5. GIS Modeled Drainage Basins
● DEM→Fill→Flow
Direction→Flow
Accumulation→Basins
● The drainage basin was
underestimated when hand
drawn
● The estimated drainage
area was kept for
calculations
6. Soils
● 30 different soil types/slopes
● The major soil type taken for
calculations:
○ Volusia Silt Loam
○ Approximately 35% of area
7. Universal Soil Loss Equation
T=RKLSCP
T - Soil Loss [Ton/Acre/Yr]
R - Rainfall Factor
K - Soil Erodibility Factor
LS - Slope Length and Gradient Factor
C - Cropping Management Factor
P - Conservation Practice Factor
8. R - Rainfall Factor
● R Factor: Nature of the rainfall
(frequency, intensity,
seasonality)
● R = 175
○ From Fig.1 Rainfall and Erosivity
index
9. K - Soil Erodibility
● Soil characteristics (infiltration,
susceptibility to detachment and
transport)
● Soil condition:
○ Volusia Silt Loam - 8.5% (110.7 acres)
○ Poor drainage/low permeability soil
○ Medium textured soil
● K = 0.32
○ From Table B-1 Characteristics of
Pennsylvania Soils
10. LS - Slope Length and Steepness Factor (GIS)
Using GIS:
● Moore and Burch Equation
○ Uses rasters of flow accumulation, slope,
and the cell resolution with the
appropriate unit conversion factors
○ Input to raster calculator:
■ (Power((("FlowAcc" *
92.46745509) / 22.13),0.4)) *
(Power((Sin("Slope_Degree" *
0.01745 / 0.0896)),1.4))
○ LS Factor = 348
■ Extremely high
■ Mean = 3.76 which is the
reasonable number to be taken
14. LS - Slope Length and Steepness Factor
● Double check LS
● Estimated using average flow length and slope
within the basin
○ Max Slope = 44.6 %
○ Mean Slope = 6.7 %
○ Longest Flow Length = 21,435 ft
○ Mean Flow Length = 11, 853 ft
● Because the average flow length is so high, it
was reduced to an estimate of Length = 2,000
ft for the sake of using Figure 3-3.
● LS = 3.6 (compared to the mean GIS value of
3.76)
15. C - Cropping Management Factor
● Ratio of soil loss from an area with
a given cover and management
relative to that from an identical
area in continuous fallow and tilled
land.
● No crops beyond hay fields that
aren’t seeded - all agricultural
fields are no longer managed and
have been left to pasture
● 75% Tall Trees, 80% ground cover
● C = 0.012
○ Table 9.1 Cover
Management C Factors for
Permanent Pasture
16. P - Conservation Management Practices
● No strip cropping/no
conservation practices
being used
● P = 1.0
17. T - Predicted Soil Loss
T = RKLSCP
T = (175)*(0.32)*(3.6)*(0.012)*(1.0) = 2.4 tonnes/acre/yr
Annual Soil loss from watershed
2.4 * 21327.67 acres = 51,595.9 tonnes/yr
18. Difference between Soil Loss &
Sediment Yield
● Sediment yield: amount of
sediment reaching or passing a
point of interest in a given period
of time (tonnes/yr)
○ Y = 11.8(Q*q)0.56KLSCP
○ Sedimentation occurs when eroded
material that is being transported
by water, settles out of the water
column onto the surface, as the
water flow slows.
● Soil Loss (Erosion): the natural
process that displaces upper
layer soil
19. Drainage Area SDR
● SDR (Sediment Delivery Ratio) = The sediment
delivered at a location in the stream system to
the overall erosion from the drainage above
that point.
Drainage Area SDR’s:
● Renfro SDR Equation:
where A = drainage area in km 2
log(SDR) = 1.7935-0.14191 log(A)
● Vanoni SDR Equation:
where A = drainage area in square miles
SDR = 0.42A-0.125
● USDA SC SDR Model:
where A = drainage area in square miles
SDR = 0.51A-0.11
What affects SDR’s?
● Drainage area, slope, relief-length ratio, runoff-
rainfall factors, land use/land cover and
sediment particle size.
● Relief Ratio (RR) -a number calculated to describe
the grade of a river or stream; difference in
elevation between the river's source and the river's
mouth divided by the total length of the river or
stream. This gives the average drop in elevation per
unit length of river
○ High relief ratio basins with fine-textured
soil-->higher SDR’s
○ Low relief ratio basins with coarse
texture-->lower SDR’s
21. Reservoir Sediment Trapping
● Reservoir = large natural or
artificial lake used as a source of
water supply or sediment
trapment
● For this project, a natural lake
was used for the reservoir
trapment
○ 36 acres = 1.568 x 107 ft2
○ Approximate depth 50’
22. Catchment Area
● Because the lake is not at the outlet of the
drainage basin, not all flow will be caught.
● A new catchment area needs to be
determined.
● A flow direction model was created in GIS
○ A polygon estimating the area of
catchment for the lake was drawn
based on flow direction
● The catchment area is: 420 acres of which
36 acres is the lake.
https://i.pinimg.com/originals/fa/db/29/fadb29a2edd39757f1a2b4ef7083215f.jpg (picture link)
No paved roads, no more than 5 residential lots
-C factor is conservative (prob more than 80% ground cover)
This picture was taken standing on a bridge as the inlet and shows sediment buildup -- it used to be a wetland and the peninsula at the bottom has developed from sediment runoff in the last 10 years
How I got the catchment area - basic estimation of area where flow goes in the direction of the lake - Discuss that accuracy is suspect because while the runoff from this area will drain to the lake, sediment entering at the inlet will have a longer settling/retention time than that entering closer towards the outlet.
