SIMULATION OF RUNOFF AND SEDIMENT YIELD FROM A HILLY WATERSHED IN EASTERN HIMALAYAS USING WEPP MODEL

1. “Simulation of runoff and sediment yield from
a hilly watershed in the eastern Himalayas,
India using the WEPP model”
JOURNAL OF HYDROLOGY 405(2011) 261-276
R.K. Singh, R.K. Panda, K.K. Satyapathy, S.V. NagchanR.K. Singh, R.K. Panda, K.K. Satyapathy, S.V. Nagchan
PRESENTED BY :
SHYAM MOHAN CHAUDHARY
(17AG62R13)

2. CONTENTS
• INTRODUCTION
• REVIEW OF LITERATURE
• PROBLEM STATEMENT• PROBLEM STATEMENT
• OBJECTIVES
• METHODOLOGY
• RESULTS AND DISCUSSION
• CONCLUSIONS

3. INTRODUCTION
• Soil erosion is a process that causes loss of fertile
topsoil and sedimentation and pollution of
surface water bodies. It is a serious agricultural
and environmental problem in many areas of the
world (Brown and Wolf, 1984)world (Brown and Wolf, 1984)
• The Water Erosion Prediction Project (WEPP) is a
computer program that predicts soil erosion by
water at the field scale. Beginning in 1985, the
WEPP model was initiated by Dr. George R. Foster
with USDA-ARS National Soil Erosion Research
Laboratory.

4. REVIEW OF LITERATURE
• Pandey et. al. (2006) in their research work “ Runoff and
sediment yield modeling from a small agricultural watershed
in India using the WEPP model ” evaluated the performance
of WEPP model for simulation of runoff and sediment yield
and obtained coefficient of determination (0.81-0.95) andand obtained coefficient of determination (0.81-0.95) and
model efficiency (0.78-0.92)
• Chandramohan et. al. (1998) in their research work
“Estimation of sediment yield and runoff from small
watershed using WEPP model” simulated rainfall data for 25
years and obtained average annual sediment yield as 4333
kgm-2 and average annual runoff at outlet as 317 mm.

5. PROBLEM STATEMENT
• Natural processes such as the production of soil
occur at an alarmingly slower rate than soil lost
by erosion.
• In India, out of 328 million hectares of
geographical area, 107 million hectares are
severely eroded.severely eroded.
• It is estimated that over 3 billion metric tons of
soil are eroded off from our country fields and
pastures each year by water erosion alone.

6. •Soil erosion is associated with adverse
environmental impacts and crop productivity loss
that makes its understanding important in assessing
food security and environmental safety.
•Monitoring and modeling of erosion can help in•Monitoring and modeling of erosion can help in
better understanding of the causes of soil erosion,
making predictions of erosion under a range of
possible conditions and plan the implementation of
preventative and restorative strategies for erosion.

7. OBJECTIVES
• To perform calibration and validation of WEPP
model for simulating the runoff and sediment
yield.
• To develop vegetative as well as structure• To develop vegetative as well as structure
based management practices to control soil
loss from the hilly watershed.

8. METHODOLOGY
STUDY AREA DESCRIPTION
• For the present study, Umroi watershed in the eastern
Himalayan region of India was selected. The watershed
is located in Ribhoi district of Meghalaya state of India.
• The watershed area is 239.44 ha and its elevation
ranges from 900 to 1240 m above the mean sea level.
Soils of the study area are formed predominantly from
the weathering of sedimentary and metamorphic
rocks.

10. The slope in the study area varies from 0 to more than 35%. The
landforms are susceptible to moderate and severe erosion, and
formation of gullies.
The climate of the watershed is humid subtropical. The annual
rainfalls were 2508.8 and 2842.5 mm in 2003 and 2004,
respectively. Nearly 87% of total rainfall was received during
May–October.May–October.
The mean monthly maximum temperature varied from 18.2°C in
January to 32.5°C in August and the mean monthly minimum
temperature varied from 3.9°C in January to 17.8°C in July.
The main crops of the watershed are paddy, ginger, turmeric,
soybean, maize, sweet potato and beans.

11. WEPP MODEL OVERVIEW
• WEPP is a physically based model. It estimates runoff
and soil loss from watershed using fundamentals of
hydrology and erosion mechanics.
• It provides estimate of spatial and temporal
distribution of soil loss or deposition in a watershed
over a broad range of conditions.over a broad range of conditions.
• Watershed sediment yield is calculated considering soil
detachment from hillslopes and channels,
transportation and deposition of sediment in hillslopes
and channels. Sediment deposition and sediment
discharge is modeled using concept of conservation of
mass.

13. EQUATONS USED IN THE MODEL
The rate of inter-rill erosion per unit area is given by
• Di = ( Ki x Ie
2 x Ce x Ge x Rs) / W
Where, Ki is the interrill erodibility constant (kg s m-4)Where, Ki is the interrill erodibility constant (kg s m-4)
Ie is the effective rainfall intensity
Ce is the effect of canopy on interrill erosion
Ge is the effect of ground cover on interrill erosion
Rs is the spacing between the rills
W is the rill width
Unit of Di is kgm-2s-1

14. Calculation of effect of canopy on interrill erosion
Ce = 1 – F e-0.34H
Where, F is the fraction of soil protected by the canopy.
H is the canopy height.
Calculation of effect of ground cover on interrill erosion
Ge = e-2.5g
Where, g is the fraction of interrill surface covered by
ground vegetation or crop residue.

15. Detachment capacity of flow
Dc = Kt(T - Tc)
Where, Kt is the rill erodibility (sm-1)
T is the flow stress acting on soil
T is the critical flow shear stress forTc is the critical flow shear stress for
detachment to occur

16. MODEL INPUTS
• CLIMATE DATA
– Rainfall data were measured by automatic as well
as non-recording type rain gauges installed in the
watershed by ICAR in 2001.watershed by ICAR in 2001.
– Maximum and minimum air temperatures,
relative humidity, sunshine hours and wind
velocity were collected from meteorological
observatory of ICAR Barapani office located 8 km
away from watershed.

17. • Slope orientation, slope length and slope steepness
were provided for each overland flow element (OFE)
on a hillslope.
• Soil input parameters included the percentage of
sand, silt and clay in soils of various hillslopes.sand, silt and clay in soils of various hillslopes.
• Plant/management input file contains information
regarding plant residue management, vegetation,
tillage parameters obtained from farmers and
scientists working in the watershed.

18. Model performance evaluation
• Split sample calibration approach was adopted
• Two years data set pertaining to 2003 and 2004
was split into two parts.
• Data for 2003 was used for model calibration and
that of 2004 for model validation.
• Data for 2003 was used for model calibration and
that of 2004 for model validation.
• Calibration was based on trial and error
procedure means several simulations were
performed adjusting parameters values until
minimum value of root mean square error was
obtained.

19. • Calibration parameters
( Pandey et. al. 2008) indicated that model is very sensitive to soil
input parameters for runoff and soil loss simulation. So the main
parameters for calibration were :
– effective hydraulic conductivity.
– interrill and rill erodibility.
– critical hydraulic shear.
• During validation, the performance of calibrated
model was judged without any changes in the input
files except the climate and plant/management files.
Model was validated for daily runoff and sediment
yield using 2004 data set.

20. Results and discussion
• Simulation of runoff

21. • Simulation of sediment yield

24. ENS (Nash Sutcliffe simulation coefficient)

25. CONCLUSIONS
• The WEPP model simulates runoff and sediment
yield satisfactorily in high rainfall and high slope
conditions of eastern Himalayas with model
efficiency greater than 0.87
• Simulation results indicated that soybean and peanut
crops in upland areas can reduce sediment yield upto
a good extent.a good extent.
• Simulation results indicated that replacing existing
tillage practice with drill no tillage system and field
cultivator may reduce the sediment yield
significantly.
• Simulation results show that installation of porous
rock fill check dams in the watershed can also control
the sediment yield.

26. THANK YOU