Eco. Env. & Cons. 27 (February Suppl. Issue) : 2021; pp. (S267-S273) Copyright@ EM International ISSN 0971–765X Quantification and classification of Groundwater - lake water exchange using conventional method S. Mahenthiran*, Madhavi Ganesan*, L. Vignesh Rajkumar* and N. Sridhar*** *School of Civil Engineering, Vellore Institute of Technology, Vellore 632 014, T.N., India ** Centre for Water Resources, Anna University, Chennai 600 025, T.N., India ***Department of Civil Engineering, Rise Krishna Sai Prakasam Group of Institutions, Ongole 523 001, Andhra Pradesh, India (Received 8 August, 2020; Accepted 15 September, 2020) ABSTRACT The Water balance of Veeranam Lake is calculated by considering all inflow and outflow components of lake. Inflow components of Veeranam lake include direct rainfall, Vadavar River inflow, ungauged catchment inflow whereas outflow components of the lake include evaporation and discharge of water for various activities (CMWSSB pumping outflow, Irrigational outflow, Lalpet Weir outflow, VNSS outflow). Ungauged catchment runoff to Veeranam Lake is estimated by Soil Conservation Service-Curve Number (SCS-CN) method. About 42% of rainfall volume in the catchment is infiltrated into the ground and 58% of rainfall volume, flow as a direct surface runoff into the Veeranam Lake. Groundwater inflow and outflow to lake are commonly expressed as net groundwater exchange and it is estimated as 53% of total outflow components of the lake. Veeranam Lake is dominated by both the inflow and outflow components of the lake. The calculated net groundwater exchange is negative and this indicates that Veeranam Lake recharges the nearby aquifer zones. Key words : Water balance, Lakes, Conventional method, Net groundwater exchange Introduction the proper function of the lake system (Bocanegra et al,. 2013). For effective management of the lake sys- Lake impart impacts on hydrological cycle because tem, individual water balance components of lake it is a function of hydrological components such as should be known. Estimation of lake water compo- surface water, groundwater and meteorological sys- nents provides a better understanding of ground- tem (Dinka et al. 2014). Lakes are closely related to water level variations in terms of both seasonal and upstream catchment and downstream ayacut area. short term scale level. Determination of lake water Irregular water management practices in the up- balance is necessary to maintain lake volume con- stream catchment area of lake affect lake environ- stant and reason for the decrease in lake storage ca- ment and in turn lake affect downstream command pacity is also assessed through it. Seepage meter is environment (Price and Maloney, 1994). Variations only point measurement and flow net provides in- in lake water level also influence the groundwater formation about the depth of groundwater flow and table condition and land-use practices. Therefore its area contributing to the lake system. The com- effective water management should be adopted for plete groundwater exchange around the lake area (*Assistant Professor (Senior), **Professor, ***Associate Professor) S268 Eco. Env. & Cons. 27 (February Suppl. Issue) : 2021 can be quantified through the lake water balance Fig. 1. The dominant soil type prevails in the study equation (Winter, 1981; Belanger and Kirkner, 1994; area is black soil and alluvial soil (CGWB, 2009). In Labaugh, 1997; Li et al., 2007; Surjeet Singh et al., this study, land use pattern is grouped into five cat- 2009; Biskop et al., 2016; Lintang Fadlillah et al., egories as agriculture, plantation, forest, scrubland 2016; Saleem and Jeelani, 2017). In the previous re- and water bodies. The study area receives high rain- search work carried out in Veeranam Lake fall in the northeast monsoon and moderate rainfall (Pruthiviraj, 2013; Latha et al., 2012; Senthilkumar in the southwest monsoon. The climate is semi-arid, and Sivakumar, 2018), the water balance of lake is which is hot during summer and moderately cool not calculated. In this paper, hydrological compo- during winter. Veeranam Lake receives water from nents (inflow and outflow) that contributes to its catchment through 8 major and 37 minor inlets Veeranam Lake is calculated individually and net during monsoon seasons (PWD, 2000). groundwater exchange between Veeranam Lake and aquifer is also calculated. Veeranam Lake clas- Methodology sification is also determined in this research work by Szesztay diagram. The water balance of Veeranam Lake is based upon the principle, change in water storage of lake (CTS) is Study Area equal to the difference between the inflow and out- flow water components of lake. The annual water The catchment of Veeranam Lake lies between balance of Veeranam Lake is calculated for the wa- 11°08ˆ 28ˆ to 11°24ˆ 59ˆNorth latitudes and ter years 2005-2015. In order to avoid the separation 79°33ˆ 05ˆ to 79°11ˆ 19ˆEast longitudes. Veeranam of the flood season, the water year (April – March) Lake catchment area is divided into five zones on is considered in the water balance equation. Inflow the basis of rain gauge stations and it is shown in components of the Veeranam Lake include direct rainfall (Rf), Vadavar River inflow (RIF), ungauged catchment inflow (UCIF) and groundwater inflow (GWIF). The outflow components of Veeranam Lake include evaporation (E), groundwater outflow (GWOF) and discharge of water for various activities (D). D comprises of CMWSSB pumping outflow (MOF), Irrigational outflow (COF), Lalpet Weir Out- flow (WOF), VNSS outflow (VOF). The runoff contri- bution to Veeranam Lake from the catchment is ungauged and runoff in this ungauged catchment is estimated by Soil Conservation Service-Curve Number (SCS-CN) method. To estimate runoff in the catchment, SCS-CN incorporates HSG (Hydro- logical Soil Group), land-use practices and Anteced- ent Moisture Conditions (AMC). The groundwater inflow and groundwater outflow are commonly expressed as net groundwater exchange (GWE) in the water balance equation. Calculated net ground- water exchange is the unknown residual term, where all other components are known terms in the water balance equation. The general water balance equation of lake sys- tem is, Inflow-Outflow = Change in storage. .. (1) The water balance equation of Veeranam Lake is expressed as below by considering the inflow and Fig. 1. Computed catchment area on the basis of rain outflow components of the lake. gauge stations RF+RIF+UCIF+GWIF = E+ D+GWOF+ CTS .. (2) MAHENTHIRAN ET AL S269 3 Where D = MOF+ COF+ WOF+ VOF .. (3) River inflow is 100 Mm and maximum inflow is After rearranging equation (2) 621 Mm3. Annual average Vadavar River inflow to Veeranam Lake is 329 Mm3 and it contributes 48% C = R +R +UC +GW E-D-GW .. (4) TS F IF IF IF- OF of total inflow components of the lake. An increase Groundwater inflow and outflow is commonly in rainfall enhances Vadavar River flow because a expressed as net groundwater exchange (Blanco- large amount of water is released from Mettur dam, Coronas et al. 2020). Grand anaicut and Lower anaicut during monsoon seasons. Thus Vadavar River inflow to Veeranam Hence GW = (GW - GW ) .. (5) E IF OF Lake is based on the intensity of rainfall in its catch- ment area. Substituting equation (5) in equation (4) gives Ungauged Catchment Inflow CTS = RF+RIF+UCIF-E-D+GWE .. (6) Runoff estimation in Veeranam Lake ungauged Rearranging equation (6), catchment is essential for the determination of lake GWE = CTS- RF- RIF-UCIF+E+D .. (7) water balance. Runoff in the catchment is influenced by both rainfall and runoff characteristics. Daily Net groundwater exchange with Veeranam Lake is rainfall data of five rain gauge stations, namely calculated in volumetric scale from water balance Senthurai, Jayankondam, Ponneri, Lalpet and equation (7). Sethiathoppe are considered as a polygon to esti- mate runoff in the ungauged catchment. Direct run- Results and Discussion off for each polygon is calculated for each rainfall event after calculation of curve number, potential Direct Rainfall maximum soil retention, initial abstraction and Rainfall is measured at Lalpet and Sethiathoppe AMC. Soil in Veeranam catchment is classified ac- rain gauge stations, which are located at the north- cording to HSG classification (USDA-SCS, 1985). ern and southern end of Veeranam Lake respec- HSG D is dominant in catchment area and it covers tively. The average rainfall of these two stations is 92.6% of total catchment area 4.16%, 2.62% and taken as daily rainfall because the major axis of the 0.55% of catchment area comprises of HSG C, HSG lake is in the north-south direction. Direct rainfall B and HSG A respectively. Infiltration and runoff contribution to Veeranam Lake is obtained on the varies from one land use pattern to another volumetric scale by multiplying rainfall with lake (Anbazhagan et al., 2005). Thus land use also pos- surface area. Annual minimum direct rainfall con- sesses significant effect on catchment runoff. 62% of tribution to Veeranam Lake is 17 Mm3 and the maxi- catchment area occupies agricultural land and mum is 42 Mm3. Annual average direct rainfalls 29.4% area covers plantation land. 8%, 0.64% and over Veeranam Lake is 31 Mm3 and it contributes 4 0.015% catchment area comprises of scrubland, wa- % of total inflow components of the Lake. High in- ter bodies and forest respectively. If HSG or land tensity of rainfall not only influences lake water use pattern is not homogenous in catchment, then storage, it also enhances the flow of water in the composite curve number is used (Anbazhagan et al., Vadavar River and Veeranam Lake catchment area. 2005). In order to standardize curve number in each polygon, it is calculated for individual HSG and Vadavar River Inflow land use pattern. The weighted curve number Vadavar River contributes major amount of water to ranges from 78 (Senthurai) to 94 (Ponneri). The cal- Veeranam Lake and its flow plays a significant role culated curve number (CNII) is for antecedent soil in water balance components of Veeranam Lake.