The document provides an outline for a presentation on the SWAT (Soil and Water Assessment Tool) hydrological model. It begins with an introduction to hydrological modeling and the development and utilities of the SWAT model. It describes the data requirements, model framework, and step-by-step procedure to run the model. A case study applying the SWAT model to the Simly Dam watershed in Pakistan is summarized. The limitations and future developments of the SWAT model are briefly discussed, followed by references.

1. Vishvjeet Tholia
Arjun P
Aswin Pragadesh R
Subhadeep Mandal
SWAT MODEL WITH RESERVOIR
MODULE

2. Presentation Outline
 Introduction
 History of development, Source
 Utilities
 Requirement of data
 Model Framework
 Procedure to run the model
 Case study
 Its limitation and drawbacks
 Future development of the model
 References

3. Introduction
 Hydrological modelling is a powerful technique for
planning and development of integrated approach for
management of water resources.
 The Soil and Water Assessment Tool (SWAT) is a small
watershed to river basin-scale model developed by the
United States Department of Agriculture – Agricultural
Research Services (USDA – ARS).

4.  Development of SWAT model is an ongoing process and it is the
successor of “the Simulator for Water Resources in Rural Basins”
model (SWRRB).

5.  It is designed to predict the impact of land use and management on
water, sediment, and agricultural chemical yields in ungauged
watersheds.
 The model breaks the entire catchment in to sub catchments which
are further divided in to hydrologic response units (HRU), land
use, vegetation and soil characteristics.
 It is semi distributed, physically and process based and data driven
river basin model.
 It is a continuous time model that operates on a daily time step.
 It is computationally efficient, and capable of continuous
simulation over long time periods.

6.  Go to SWAT website: https://swat.tamu.edu/
 SWAT is a public domain software enabled model actively
supported by the USDA Agricultural Research Service at the
Blackland Research & Extension Center in Temple, Texas, USA.

7. UTILITIES
• SWAT model is used to run hydrological models to get water
balance ratios like: stream flow-precipitation ratio, base flow-total
flow ratio, ET-precipitation ratio etc.
• It provides maximum upland sediment yield.
• In reservoir models, it provides average values of trapping
efficiency, water losses, and reservoir trends.
• SWAT model also deals with nitrogen and phosphorus cycles, plant
growth, landscape nutrient losses, land use summary, instream
processes, and point sources.
• Quantifying the impacts from land use changes on the runoff and
modelling the long term impact of management practices
The utility of SWAT model is extensively vast in all hydrological field.

8. Data Requirement
The inputs, used by this model, are -
 Daily rainfall data,
 Maximum and minimum air temperature,
 Solar radiation,
 Relative air humidity and
 Wind speed used
Using that data, it is able to describe water and
sediment circulation, vegetation growth and
nutrients circulation. Based on amount of
precipitation and mean daily air temperature rate of
snowfall can be determined.

9. Model framework
INPUTS
 Hydrological
parameters
 Meteorological
parameters
 DEMs
 Land Use/Land
cover maps
OUTPUTS
 Surface Runoff
 Evapo-
Transpiration
 Total Flow
 Infiltration
Soil Water
Assessment
Tool
(SWAT)

10. Simulation of SWAT
hydrological
parameters of a
watershed
LAND PHASE of
Hydrologic cycle
ROUTING PHASE
of Hydrologic cycle

11. Simulation of SWAT
hydrological
parameters of a
watershed
LAND PHASE of
Hydrologic cycle
ROUTING PHASE
of Hydrologic cycle

12.  Calculation of Runoff volume(Land Phase)
SCS – CN Method
 Runoff from the
catchment (Q)
 Retention Parameter (S)
 Curve Number (CN)
Range (0 ≤ CN ≤ 100)
Ia = 0.2*S

13.  Peak Runoff rate (Qpeak)
where
C - runoff coefficient
i - mean intensity (mm/hr) of
precipitation for a duration
equals to tc and an
exceedance probability P
A – Subbasin area (Km2)
 Time of Concentration (Tconc)
 Peak Runoff rate Method

14.  Overland flow Time of concentration (Tov)
 Channel flow Time of concentration (Tch)
 Modified Peak Runoff rate (Qpeak)
αtc = fraction of daily rainfall that occurs during the time of concentration

15. Water Balance approach (SWAT - WB)
Where
EDC - effective depth of the soil
profile
ε - total soil porosity
θ - volumetric soil moisture for each
day
Where
Q – Surface Runoff
P - Precipitation
• If the rain event is LARGER in volume than τ, the soil will saturated
and surface runoff will occur
• If the rain event is LESS than τ, the soil will not be saturated and there
will be no surface runoff

16. Penman Monteith, Priestly- Taylor and Hargreaves methods
are used for the estimation of evapotranspiration.

17. In order to obtain accurate forecasting of water, nutrient and sediment
circulation, it is necessary to simulate hydrologic cycle which integrates
overall water circulation in the catchment area and hence the model uses the
following water balance equation in the catchment.
Where SWt is the humidity of soil, SWo is base humidity, Rv is rainfall
volume in mm water, Qs is the surface runoff, Wseepage is seepage of
water from soil to underlying layers, ET is evapotranspiration, Qgw is
ground water runoff and t is time in days).
In case of base flow calculation,

18. Simulation of SWAT
hydrological
parameters of a
watershed
LAND PHASE of
Hydrologic cycle
ROUTING PHASE
of Hydrologic cycle

19. Routing Phase
Muskingum routing method
Variable storage method
 SWAT uses Manning’s equation to define the rate and
velocity of flow

20. SWAT
Model
Simulation
Sensitivity
Analysis & Model
Calibration
Model
Validation Output
Reading
Reports
Parameters
Optimal
Values
HRU
Definition
Watershed
Discretization
Discharge
Data
Discharge
Data
GIS
ProcessingInput Data
DEM
Meteorol
ogical
data
Weather
Time Series
SoilLand Use
Location of
Weather
Stations
Complete SWAT Model Project Setup

21. Procedure To Run The Model (Step by Step)

22. SWAT Tool bar
Step 1: SWAT Project Setup
 Click on ‘SWAT Project Setup’

23. Geodatabase
( in *.mdb format)
Creation of SWAT Project

24. Step 2: Watershed Delineator
Open DEM Setup
Stream Definition
Stream network
Outlet and Inlet Definition
Outlet Selection and
definition
Subbasin Parameters and
Add Reservoir

26. Step 3: HRU Analysis
 Hydrologic Response units are portions of a subbasin that possess
unique landuse/management/soil attributes.
 In a watershed ,the first level of subdivision is the subbasin which
will contain at least one HRU, a tributary channel and a main channel
or reach. As a general rule, a given subbasin should have 1-10
HRUs.

27. An HRU (the total area in the subbasin with a particular
landuse, slope and soil) is not synonymous to a field
(While individual fields with a specific landuse,
management and soil may be scattered throughout a
subbasin) ,these areas are lumped together to form one
HRU.
HRUs are used in most SWAT runs since they simplify a
run by lumping all similar soil and land use areas into a
single response unit. It is often not practical to simulate
individual fields.

28. Step 3: HRU Analysis -.a. Land Use

29. https://earthexplorer.usgs.gov.in

30. Step 3: HRU Analysis -.b. Soil

31. Step 3: HRU Analysis -.c. Slope

32. Step 3: HRU Analysis; HRU Definition

33. Step 3: HRU Analysis; HRU Analysis Report

34. Step 3: HRU Analysis; HRU Analysis Report

35. Step 4: Write Input Tables

36. Step 5: Edit SWAT Input

37. Step 6: SWAT Simulation

38. SWAT Output Window

39. SWAT Checker Window

40. SWAT Checker Window

41. Case Study
• Hydrological modeling of the Simly Dam watershed
(Pakistan) using GIS and SWAT model
Shimaa M. Ghoraba
To estimate the volume inflow to the Simly Dam, for
developing efficient decision framework to facilitate,plan
and access the management of reservoir
Objective

42. Study Area
Fig.1: Location map of the Simly Dam watershed area in Pakistan

43. Materials and Methods
Digital Elevation Model (DEM) of the watershed area (a) Delineation of sub-basins of watershed; (b) Land
use map; (c) Soil map; (d) Location of weather
stations

44. Results and Discussion
Fig .3. Annual observed and simulated stream flow for the calibration period (1990–2001).

45. Contd…
Fig.4. Annual observed and simulated stream flow for the validation period (2002–2011).

46. Contd…
Fig.5: Comparison of annually observed and simulated dam outflow for the calibration and
validation period

47. Contd…
Fig.6: Comparison of monthly observed and simulated stream flow for the calibration period (1990–2001).

48. Fig.7: Comparison of monthly observed and simulated stream flow for the validation period (2002-2011)
Contd…

49. Fig.8: Average annual water balance as a relative percentage to precipitation for calibration and validation years
Fig.9:Comparison of monthly observed and simulated dam inflow for the calibration and validation periods.

50. Conclusions
1) In this study calibrated SWAT model has been produced
good simulation results where Water balance components
such as surface runoff, lateral flow, base flow and
evapotranspiration have been simulated.
2) The monthly inflow to Simly Dam estimated by the model
and the simulated values shows very close agreement
(Coefficient of Determination (R2), NSE).
3) The performances of the model can be enhanced furthermore
by integration of some other climatic data such as solar
radiation, humidity and wind.

51.  The main weakness of the model is a non-spatial representation
(site- specific, not robust model) of the HRU inside each
subcatchment. This also kept the model simple and supported
application of the model to almost every catchment.
 Wide range of different data needs to be obtained to run the
model and numerous parameters needed to be modified during
the calibration which needs a lot of patience to deal with.
 The model does not allow simulations of multicultural plant
communities which are common in organic farming, grasslands
and forests as they were originally developed for monocultures.
Limitations and drawbacks of SWAT

52.  Some users have addressed weaknesses in SWAT by component
modifications, which support more accurate simulation of specific
processes or regions, or by interfacing SWAT with other models. Both of
these trends are expected to continue.
 The SWAT model will continue to evolve in response to the needs of the
ever increasing worldwide user community and to provide improved
simulation accuracy of key processes.
 A major challenge of the ongoing evolution of the model will be
meeting the desire for additional spatial complexity while maintaining
ease of model use. This goal will be kept in focus as the model
continues to develop in the future.
 Future development of the model

53. [1] Gassman, P. W. et al (2007) . “The soil and water assesment tool:
histoorical development, applications, and future research directions.”
American Society of Agricultural and Biological Engineers ISSN 0001-
2351, Vol. 50(4): 1211-1250.
[2] J. R. Williams and J. G. Arnold. (2010) “History of Model
Development at Temple, Texas” Presentation.
https://swat.tamu.edu/docs/swat/conferences/2010/presentations/Opening.
Williams.pdf
[3] Gayathri K Devi, Ganasri B P, Dwarakish G S (2015).” A Review on
Hydrological Models.” Aquatic Procedia 4 ( 2015 ) 1001 – 1007.
www.elsevier.com/locate/procedia.
[5] SWAT Manual. https://swat.tamu.edu/documentation/
[6]"SWAT: Soil & Water Assessment Tool". Texas A&M University. Retrieved 1
March 2012.
References: