Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed

GRD Journals | Global Research and Development Journal for Engineering | Emerging Research and Innovations in Civil Engineering (ERICE - 2019) | February 2019

e-ISSN: 2455-5703

Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India 1D.

P. Navadiya 2 Dr. T. M. V. Suryanarayana 1 P.G. Student 2Associate Professor 1,2 Department of Water Resources Engineering and Management Institute (WREMI) 1,2 The Maharaja Sayajirao University of Baroda, Samiala-391410 Abstract Extraction of watershed parameters using Remote Sensing and Geographical Information System (GIS) and use of mathematical models is the current trend for hydrologic evaluation of watersheds. The Soil and Water Assessment Tool (SWAT) having an interface with QGIS is adopted in the present study for the determination of various outputs, viz. Surface runoff, Base flow, Percolation, Potential evapotranspiration and Sediment load in Vishwamitri river watershed in Vadodara, Gujarat, India. Various data types required as input for the study comprises of Digital Elevation Models (DEM), Landuse/Landcover maps, Soil maps and Climate data. The Stream considered lies between 22° 13' to 22° 21' of north latitude and 73° 12' to 73° 13' of east longitude.

Providing require inputs, SWAT model was simulated for 2003 to 2014. Analysis reveals that maximum rainfall was obtained in 2005 and minimum rainfall is obtained in 2009. In 2005, it is found out that the Precipitation is maximum, and the corresponding surface runoff in sub-basins 3 and 5 are having highest values of 767.04mm and 747.87mm respectively. Similarly, baseflow in sub-basin 3 & 5 are having lowest values of 298.20mm and 316.40mm respectively. The percolation in sub-basin 3 & 5 are also having the lowest values of 363.10mm and 381.70mm respectively. The Surface runoff, Base flow and Percolation were found out to be around 48%, 20% and 32% of the precipitation occurred in 2005, while amongst the average precipitation of the total period considered, the Surface runoff, Base flow and percolation are found out to be around 38%, 18% and 24% respectively.

Keyword- QGIS, QSWAT, Surface Runoff, Base Flow, Percolation, PET, Sediment Load __________________________________________________________________________________________________

I. INTRODUCTION A watershed is a catchment basin that is bound with topographic features. The total amount of water that falls as rains within a catchment area will either flow as surface runoff in the river which drains the basin or sinks into the ground to become ground water.

There are numbers of hydrological model applied for watershed evolution. Large numbers of parameters are involved in hydrological model that are used for surface runoff, base flow, subsurface runoff, evapotranspiration and lateral flow etc.

Remotely sensed data provides valuable and real-time spatial information on natural resources and physical parameter. GIS is an effective tool in watershed modeling as remote sensing derived information can be well integrated with the conventional database for estimating runoff which can help in planning suitable soil and water conservation measures. Use of mathematical models for hydrologic evolution of watershed is the current trend along with extraction of watershed parameters using remote sensing and Geographical Information System. The current study was undertaken on the application of the SWAT model which integrates the GIS information with attribute database to estimate the various parameters.

SWAT (Soil and water assessment tool Arnold 1998) has proven very successive application in water assessment of hydrology.This model is physical based and offers continuous time stimulation.

II. MATERIALS AND METHODS A. Study Area The study area Vishwamitri River is located between 22° 00” and 22°45” of North Latitude and 73°00” and 73°45” of East Longitude in Panch Mahals, Vadodara and Bharuch districts, in Gujarat State, India. The watershed has dendrite drainage pattern.

The total geographical area of the watershed is 1134.15 km2. The topography of the area is generally flat to gently sloping, with the elevation ranges from 795 m to 16 m above mean sea level.

The average weighted annual rainfall is 1068.54 mm, maximum wighted annual rainfall is 1554 mm and minimum weighted annual rainfall is 476mm. Fig. 1 shows the location of the study area named Vishwamitri River watershed.

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Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India (GRDJE / CONFERENCE / ERICE - 2019 / 071)

Fig. 1: Study area location

B. Model Description SWAT (version SWAT2012) is used in the present study. It is a physically based continuous event hydrologic model developed by the U.S. Department of Agriculture Research Service (USDAARS), which operates on a daily time step and uses physiographical data such as elevation, land use, and soil properties as well as meteorological data. The SWAT model is mainly used to predict the impact of land-management practices on water, sediment etc. in large basins with varying soils, land use, and management over long periods of time. The hydrological processes included in the model are surface runoff, Potential evapotranspiration (PET), percolation, infiltration, Base flow etc.

The effects of spatial variations in topography, land use–land cover, hydrologic soil types, and other characteristics of watershed hydrology are incorporated by dividing a basin into several subbasins based on stream drainage areas.

The SWAT model uses Natural Resource Conservation Service (NRCS) curve number method (SCS 1972) for estimating surface runoff (Qsurf ). The fundamental hydrology of a watershed in SWAT is based on the following water balance Eq. 1, which is based on mass balance that calculates the change in soil water content (SW t) t

SWt = SW0 + ∑

i=1

(R day − Q surf − Ea − Wseep − Q gw )

(1)

where SWt = final soil water content (mm); SW0 = water content available for plant uptake, defined as the initial soil water content minus the permanent wilting point water content (mm); t = time in days; Rday = rainfall (mm); Qsurf = surface runoff (mm); Ea = evapotranspiration (mm); Wseep = percolation (mm); and Qgw = return flow (mm).

C. Runoff Calculation by SWAT SWAT uses the SCS curve number method (USDA Soil Conservation Service, 1972) to compute surface runoff volume for each HRU. The SCS runoff equation is an empirical model that was developed to provide a consistent basis for estimating the amounts of runoff under varying land use, soil types, and antecedent moisture conditions (Rallison and Miller, 1981). The SCS curve number Eq. 2 below: Q surf =

(Rday−0.2S)2 (Rday+0.8S)

(2)

Where, S is the retention parameter (mm). In this equation the initial abstraction, which includes surface storage, interception and infiltration prior to runoff, is approximated as 0.2S. The retention parameter is find out by using Eq. 3 shown below: 1000 S = 25.4 ( − 10) (3) CN CN has a range from 30 to 100; lower numbers indicate low runoff potential while larger numbers are for increasing runoff potential. The lower the curve number, the more permeable the soil is. As can be seen in the curve number equation, runoff cannot begin until the initial abstraction has been met. The runoff curve number is based on the area's hydrologic soil group, land use, treatment and hydrologic condition.

D. Potential Evapotranspiration Potential Evapotranspiration is a collective term that includes evaporation from the plant (transpiration) and evaporation from the water bodies and soil. SWAT provides three options for PET calculation: Penman-Monteith (Monteith, 1965), Priestley-Taylor (Priestley and Taylor, 1972), and Hargreaves (Hargreaves et al., 1985) methods.For this study, the Penman-Monteith method was selected as this method was widely used for many studies.

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Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India (GRDJE / CONFERENCE / ERICE - 2019 / 071)

E. Base Flow Base flow is computed by SWAT using this Eq. 4 shown below: Qgwi = e −αgwΔt ⋅Qgw,i−1 +(1− e −αgwΔt )⋅ wrchrg,i (4) Where, Qgw,i-1 is the groundwater flow into the main channel on day i-1 (mm), αgw is the base flow recession constant, and Δt is the time step (1 day).

F. Percolation The recharge to the aquifer on a given day is calculated by Eq. 5 shown below: Wrchrg,i = Wrchrg,i−1*e (−1/ δgw) + wseep,i * 1-e( −1/δgw ) (5) Where, δgw is the delay time or drainage time of the overlying geologic formations (days), Wseep,i is the total amount of water exiting the bottom of the soil profile on day i (mm), and Wrchg,i-1 is the amount of recharge entering the aquifer on day i-1 (mm).

G. Input Data The model input data required for hydrological simulation of a River Basin is categorised broadly in two types-spatial data and non-spatial data. Hydrological simulation of the river basin requires certain type of data before simulation. The spatial data required

by SWAT for hydrological simulation of basin are: DEM, LULC & SOIL MAP. On the same lines of Spatial Data, an extensive data set is required for non-spatial data type. They are temperature, precipitation, relative humidity, solar radiation and wind speed.

1) Digital Elevation Model (DEM) The DEM is the raster data consisting of sampled array of pixels containing elevation values representing ground positions at regularly spaced intervals. It is used for watershed and stream network delineation and the computation of several geomorphological parameters of the catchment including slope for HRUs. The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate the most complete high resolution digital topographic database of Earth.

For the present analysis SRTM-90M utilized & projected DEM to WGS_1984_UTM_Zone_43N coordinate system is used in QSWAT Watershed Delineator for watershed delineation.

The Shuttle Radar Topography Mission (SRTM), C band radar obtained elevation data on a near-global scale has been utilized for the area under study.

2) Landuse /Land Cover The land use / land cover data of the study area is required for HRU definition and subsequently for assigning the Curve Numbers (CN) to the land areas for runoff computations and hydrological analysis. The land use of an area is one of the most important factors that affect surface erosion, runoff, and evapotranspiration in a watershed during simulation. Land use/Land cover classified data under The Global Land Cover by National Mapping Organizations (GLCNMO) is used for this study.

3) Soil Map The soil map of the study area has been obtained from United Nations University UNU-INWEH. 4) Defining Climate Database The data set used for the present work are daily rainfall data, daily temperature data, daily relative humidity, Daily solar radiation and daily wind speed for years 2003 to 2014. These data corresponds to Bhaniyara station located at latitude & longitude of 22°39´ & 73°26´ respectively, near to Vadodara city and are collected from State Water Data Center (SWDC), Gandhinagar.

III. MODEL SET UP QSWAT delineates a watershed into sub-watersheds based on DEM and drainage network. After the DEM is imported in the model, a masking polygon of the study area was created in QGIS Info grid format and is then loaded in the model, in order to extract out exclusively the area of interest. The area delineated by the QSWAT interface was found to be the total geographical area of the watershed, which is 1134.15 KM2 & total 7 subbasins where created. One of the main sets of input for simulating the hydrological processes in SWAT is climate data, which comprises of precipitation, maximum and minimum temperature, wind speed, relative humidity and the weather generator (.dbf) file. The climate data for study periods were prepared in .dbf format and then imported in the SWAT model. Finally the SWAT model is run to simulate the various hydrological parameters. The flow chart of SWAT model is shown in Fig. 2.

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Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India (GRDJE / CONFERENCE / ERICE - 2019 / 071)

Fig. 2: The flow chart of methodology and model setup

A. SWAT Simulation The SWAT Simulation menu allows us to finalize the setup of input for the SWAT model and to run the SWAT model after this sensitivity analysis and auto-calibration has been carried out. Providing required inputs, SWAT model was simulated for 2003 to 2014.

IV. RESULTS AND DISCUSSION A. Final SWAT Land use/Soil Classes The Vishwamitri River catchment is considered for the study and in SWAT that is divided into 7 small sub-basins, as shown in Fig. 3. The results generated by SWAT for the entire basin, as well as each sub-basin, are discussed in detail.

The SWAT Land use classes are prepared by using The Global Land Cover by National Mapping Organizations (GLCNMO) dataset. After defining land use classes as per SWAT, there are thirteen land use classes in the Vishwamitri basin and are given in Table1.

Landuse code URMD CRDY CRIR CRGR CRWO GRAS SHRB FODB FODN FOEB WATR WEWO TUHB

Name Area (ha) RESIDENTIAL-MEDIUM DENSITY 38.91 DRYLAND CROPLAND AND PASTURE 438.91 IRRIGATED CROPLAND AND PASTURE 175.1 CROPLAND/GRASSLAND MOSAIC 38.91 CROPLAND/WOODLAND MOSAIC 3891.85 GRASSLAND 6863.08 SHRUBLAND 194.55 DECIDUOUS BROADLEAF FOREST 9510.57 DECIDUOUS NEEDLELEAF FOREST 8821.85 EVERGREEN BROADLEAF FOREST 66686.81 WATER 38.91 WOODED WETLAND 16155.75 HERBACEOUS TUNDRA 560.31 Table 1: Landuse land cover Classification

% Watershed 0.03 0.39 0.15 0.03 3.43 6.05 0.17 8.39 7.78 58.8 0.03 14.24 0.49

Fig. 3: View showing subbasin-wise classification of vishwamitri river & vadodara city

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Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India (GRDJE / CONFERENCE / ERICE - 2019 / 071)

Looking at the average of values of the data considered, average annual rainfall is 1076 mm and after infiltration of 289.50mm and Evapotranspiration of 411.20mm, Surface runoff of 375.55mm is produced, which are inturn 26.91%, 38.22% and 34.91% of the average rainfall in the area considered for the study.

It can be concluded that the change in land use land cover of various sub-basins results in the change in the surface runoff, baseflow and percolation. It can be observed that high urban area particular 3, 5 and 6 shows distinct behaviour than other subbasins of the same catchment.

From Fig. 3 & Fig. 4 (shown below), one can identify that most part of the Vadodara city is located in sub-basin 3 and 5, and the results indicate that the same yield high surface runoff, low baseflow and low Percolation, as compared to the other subbasins.

Fig. 4: Surface Runoff variation with Precipitation each sub-basin From Fig. 4, Fig. 5 and Fig. 6, it can be analysed that in any year, surface runoff, baseflow and percolation of each subbasin are varying, though the precipitation is same for a given year.

Fig. 5: Baseflow variation with Precipitation each sub-basin

Fig. 6: Percolation variation with Precipitation each sub-basin

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365

Analysis of Hydrologic Parameters using SWAT Model: A Case Study of Subbasin of Vishwamtri Watershed, Gujarat, India (GRDJE / CONFERENCE / ERICE - 2019 / 071)

The results indicates that maximum & minimum surface runoff of sub-basin 1; sub-basin 2; sub-basin 3; sub-basin 4; subbasin 5; sub-basin 6 and sub-basin 7 are found out to be 658.04mm & 30.519mm; 680.502mm & 35.773mm; 767.042mm & 54.904mm; 698.4mm & 39.816mm; 747.87mm & 50.388mm; 712.694mm & 42.624mm; 692.1mm & 38.173mm respectively.

The results indicates that maximum & minimum baseflow of sub-basin 1; sub-basin 2; sub-basin 3; sub-basin 4; sub-basin 5; sub-basin 6 and sub-basin 7 are found out to be 496.64mm & 35.32mm; 475.42mm & 30.04mm; 395.267mm & 8.27mm; 458.516mm & 25.57mm; 412.67mm & 11.27mm; 444.50mm & 20.6mm; 465.221mm & 27.26mm respectively.

The results indicates that maximum & minimum percolation of sub-basin 1; sub-basin 2; sub-basin 3; sub-basin 4; subbasin 5; sub-basin 6 and sub-basin 7 are found out to be 567.2mm & 85.66mm; 544.6mm & 81.33mm; 458.7mm & 65.48mm; 527.2mm & 78.12mm; 478.1mm & 68.72mm; 512.9mm & 75.48mm; 532mm & 79mm respectively.

V. CONCLUSIONS In 2005, it is found out that the Precipitation is maximum, and the corresponding surface runoff in sub-basins 3 and 5 are having highest values of 767.04mm and 747.87mm respectively. Similarly, baseflow in sub-basin 3 & 5 are having lowest values of 298.20mm and 316.40mm respectively. The percolation in sub-basin 3 & 5 are also having the lowest values of 363.10mm and 381.70mm respectively.

Analysis reveals that maximum rainfall was obtained in 2005 and minimum rainfall is obtained in 2009. The Surface runoff, Base flow and Percolation were found out to be around 48%, 20% and 32% of the precipitation occurred in 2005, while amongst the average precipitation of the total period considered, the Surface runoff, Base flow and percolation are found out to be around 38%, 18% and 24% respectively.

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[2] Jacobs, J.H. and R. Shrinivasan,(2005). Application of SWAT in developing countries using readily available data.

Proceeding, 3rd International SWAT conference, Zurich.

[3] Panhalkar S.,(2014). Hydrological modeling using SWAT model and geoinformatic techniques. National Authority for Remote Sensing and Space Sciences. The Egyptian Journal of Remote Sensing and Space Sciences. 17, 197–207.

[4] Shivhare, V., Goel, M., Singh, C.(2014). Simulation of surface runoff for upper tapi subcatchment area (burhanpur watershed) using SWAT. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-8, 2014 ISPRS Technical Commission VIII Symposium, 09 – 12, Hyderabad, India.

[5] Verma, A., Jha, M.(2015). Evaluation of a GIS-Based Watershed Model for Streamflow and Sediment-Yield Simulation in the Upper Baitarani River Basin of Eastern India. Journal of Hydrologic Engineering. Volume 20, SPECIAL ISSUE: Soil Erosion and Sediment Yield Modeling.

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[7] SWAT-X. 2015. Arc View SWAT, version 2015. From Soil and Water USDA Soil conservation service, 1972. “Hydrology, In National Engineering Handbook”, U.S. Department of Agriculture-soil Conservation Service: Washinton, DC. [8] User manual of SWAT

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