An Assessment of the Future Water Availability of Ajoy River Catchment with Special Emphasis on Soil Moisture Accounting Ms. Sujana Dhar School of Water resources Engineering Jadavpur University Kolkata 700032 sujanadhar_ju@rediffmail.com Pankaj Kumar Roy School of Water resources Engineering Jadavpur University Kolkata 700032 Asis Mazumdar School of Water resources Engineering Jadavpur University Kolkata 700032 Abstract This paper assesses and offers a future projection of water availability scenario of the Ajoy river catchment in Eastern India with emphasis on soil moisture accounting. The importance of including soil moisture within a soil profile has been included in this work .An attempt is made to estimate future water availability keeping into account the variation of soil moisture properties. Using the changed climate scenario, generated by the Regional Model of Hadley Research Centre (Version II), simulation of the projected water availability scenario has been performed with the aid of the hydrologic model of HEC HMS (Hydrologic Modeling System) developed by the US Army Corps of Engineers. The streamflow and its peak are seen to display decreasing trends from 2041-50. Introduction Water is a renewable but finite source. In India, the agricultural sector uses more than 80% of the total water; on the one hand with only 122 billion cubic meters presently estimated as the maximum utilizable resource, the present per capita availability in India comes to about 1250 cubic meters. This puts India in the category of ‘water stressed’ countries. Depletions in water tables and diminishing river flows are manifestations of the growing stress on water resources. Compared to other components of the hydrologic cycle, the volume of soil moisture is small, nonetheless, it is of fundamental importance to many hydrological, biological and biogeochemical processes. Soil moisture is one of the several useful parameters that are amenable to remote sensing at global, regional and larger scales. Soil moisture is an important parameter in many diverse applications in agriculture, hydrology and meteorology. The knowledge of soil moisture content in the surface layers helps to plan agronomic operations, like irrigation scheduling, partitioning rainfall into runoff and infiltration components. Soil moisture is a key variable in controlling the exchange of water and heat energy between the land surface and the atmosphere through evaporation and plant transpiration. As a result, soil moisture also strongly affects the part of precipitation that runs off into nearby streams and river. Soil moisture incorporation is a mandatory part while calculating the water budget of the soils The integration of soil moisture data allows better control of the evolution of the forecasting model and improves its performance greatly. This paper considers input parameters of four catchments of the Ajoy river basin, spread over West Bengal and Bihar in eastern India namely, Natunhat, Jamtara, Sikatia and Gheropara in order to generate soil moisture relatio nships from 2041-2050.Water Availability status for 2041-2050 has been accomplished by computing soil moisture properties such as canopy overflow, soil infiltration and ET which have been determined and illustrated over the mentioned period of ten years.  Fig 1. Ajoy River Catchment , showing Jamtara in Dumka and Natunhat in West Bengal, India. Location & Extent The catchment located in the plateau of Santhal Parganas, lies between 23? 27’ to 24? 40’ N latitudes and between 86?15’ to 88?10’ E longitudes and is covered by Survey of India toposheets nos. 72L/6,7,8,10,11,12,15,16, 73I/13, 73M/ 1,2,5,6,7,10,11,14,15 and 79A/1 in the scale of 1:50,000 and 1:36,360. It spreads over Deoghar, Dumka, Giridhi, Munger & Jamui district of Bihar and Burdwan and Birbhum district of West Bengal. The Ajoy river emerges from the forest covered hills of Chakai block in Munger district of Bihar and flows over a length of 132km in Jharkhand, enters West Bengal near Kalipahari and flows over a length of 144 kilometers over West Bengal and falls into the Bhagirathi, which is a distributary emerging out of river Ganga, near Katwa. A small number of riverlets like Kedhasa and Darwa join it at the upper reaches. The total basin area of Ajoy river is 6,888 square km. The basin area in Jharkhand is is 3,554 square km, which is 51.6 percent of the total basin area. In West Bengal, the basin area is 3,334 square km, which is 48.4 percent of the total. The basin area in Jharkhand is hilly whereas that in West Bengal is mostly plain. About 7 percent of the total area is under forests and about 63 percent is under cultivation. The observed discharge for two gauge stations in Ajoy river located at Jamtara, in Jharkhand and Natunhat in Barddhaman district in West Bengal was collected. The river basin between these two gauge stations represents the study area. The Jamtara station is located at latitude 23?58’18’’ and longitude 86?54’25’’ and the Natunhat station is located at latitude 23?32’44’’ and longitude 87?54’25’’. The basin area between these two stations is about 2906 square km. Average annual precipitation of the study area is about 120 cm. The elevation of the study area ranges from 232m to 48m. The major portion of the study area is under agriculture. Soils of the study area are red loamy soil, older alluvium and younger alluvium. The average slope varies from 1 in 700 to 1 in 2500. Physiography, Relief and Drainage Physiographically, the area is (i) hilly and undulating land in the northwest of the catchment (ii) gently undulating and rolling uplands that are dissected by narrow valleys, depressions and interrupted by scattered and isolated hillocks covering almost the major portion of the catchment in Bihar (iii) the valley lands mostly confined along the main tributaries (iv) river terraces and flood plains in the lower catchment areas The drainage pattern is dendritic and sub dendritic and is parallel in the lower regions. Geology The common rock of Archean system of this area is gneiss with different mineralogic composition. Pegmatites are found as veins. The middle of the catchment area comprises the Gondwana system, which is dominated by sand stone, shales and clays with local coal seams. The southern portion of the catchment comprises of alluvium of the Ganga basin. Soil The soils encountered in the hilly region and hillrocks of the very steep slopes are yellowish brown to reddish brown, very shallow to moderate deep, light texture (skeletal). In the foot hills undulating and rolling upland of gently to moderately sloping area (especially on the upper part of the catchment) the soils are yellowish brown to yellowish red and dark brown having red mottle at places, moderately deep to very deep, coarse to fine loamy textured. In the lower convex and depression of very gently to gently sloping areas the soils are of fine loamy and fine, pale brown to grey and dark grey, with red mottles, deep to very deep; and in the river terrace and levee of very gently to gently sloping areas developed over recent alluvium; the soils are fine to coarse loamy. Water accounting of Ajoy river basin has been performed in order to give planners a clear view of water activity in a river basin. Where its going and how productive it is per cubic meter and it is available for usage. Water accounting helps water managers explore where there is potential for conserving water, where the productivity of water can be increased and where there is scope for development of additional water resources. Methodology The hydrologic simulation package HEC-HMS has been used for the evaluation of future water availability status of Ajoy river basin with special emphasis on soil moisture accounting. The HEC-HMS is the US Army Corps of Engineers’ hydrologic modeling system and was developed by the Hydrologic Engineering Centre (HEC). The hydrologic model simulates precipitation and routing process. The use of the model requires input of daily rainfall, soil condition and hydrometeological data. Application of Geographical Information System GIS has been applied in this paper in order to generate input data required by HEC HMS. The outputs of GIS i.e. landuse / landcover map (Fig 1a) and drainage map (Fig 1b) have been generated for better accuracy of results. Such maps allow a better understanding of land utilization aspects used in turn by HEC HMS simulation model. It is a well-known fact that Ajoy River Catchment is dominated by agricultural land use. GIS along with Remote Sensing techniques make significant contribution in preparing different types of agricultural inventories and in collecting land use data, particularly agricultural land use data.  Fig 1a. Land Use Map of parts of Ajoy River catchment rain lends information on how much land is double cropped and how much cropped land is subject to flooding, information that is very pertinent to this model simulation in and around Natunhat, Barddhaman District.  Fig 1b. Drainage Map of parts of Ajoy River catchment in and around the chosen rain gauge station, Natunhat, Barddhaman District. Simulation Of Soil Moisture Accounting A soil moisture accounting (SMA) algorithm was developed by the Hydrologic Engineering Center for the Hydrologic Modeling System (HEC-HMS). HEC-HMS succeeds the widely used HEC-1 hydrologic model as part of the next generation (NEXGEN) of hydraulic and hydrologic modeling software under development at the U.S. Army Corps of Engineers Hydrologic Engineer Center (HEC). SMA method allows for long-term continuous simulation of hydrologic processes that occur and change over time in a watershed. This is achieved by simulating the movement of precipitation through storage volumes that represent canopy interception, surface depressions, the soil profile and two groundwater layers. Computational components of this algorithm also include evapotranspiration (ET), surface runoff, and groundwater flow. This paper details the computational steps and equations used in the SMA loss method to simulate these processes. Results of model application to simulate runoff for Ajoy river watershed are described. HEC-HMS soil moisture accounting model is a continuous model i.e. it is a model that simulates both wet and dry behavior. The HEC-HMS SMA model is patterned after Leavesley’s Precipitation-Runoff Modeling System (1983) and is described in detail in Bennett (1998). SMA model parameters were determined by calibration with observed data ranging from 1997-2001.In this iterative process, parameter values are proposed, the model is exercised with these parameters and precipitation inputs. The resulting computed hydrograph is compared with an observed hydrograph for the same period, in this case 1997-2001. The soil profile storage represents water stored in the top few inches of the soil. Water infiltrates into the soil profile from the combined precipitation passing beyond canopy interception and any water in surface depression storage. The potential infiltration rate is as follows: I pot soil = I max soil – [S soil(t) / S max soil] I max soil where I is the potential or maximum infiltration for the soil and S is the maximum or current storage. Actual infiltration is the lesser of the water available for infiltration and the potential infiltration. Outflows are percolation to the upper groundwater layer and evapotranspiration. The percolation rate to the upper groundwater layer is as follows: P potsoil = P max [S soil(t)/S max soil ] [1- Supgw(t)/S max upgw ] where P is the maximum or potential percolation rate out of the soil layer and S is the maximum or current storage in the soil or upper groundwater layer. The evapotranspiration out of the soil profile is computed from the soil profile, tension zone storage, and potential evapotranspiration computed by the meteorologic model as follows: E act soil/ E pot soil = f [S soil(t) / S max tension ] where E is the actual or potential evapotranspiration from the soil profile and S is the maximum tension or soil profile storage. Water percolates into the upper groundwater layer from the soil profile, from the upper groundwater layer to the lower groundwater layer, and from the lower groundwater layer out of the system. Water in storage in a groundwater layer can be passed laterally out of the system to the linear reservoir base flow model. Percolation from the upper groundwater layer to the lower groundwater layer is computed as follows: P pot upgw = P max upgw [S upgw(t) / S max upgw ] [1- S low gw(t)/S max low gw ] where P is the maximum or potential percolation and S is the maximum or current storage in the upper or lower groundwater layer. Percolation from the lower groundwater layer out of the system, sometimes called deep percolation, is computed as follows: P pot low gw = P max low gw [ S lowgw(t) / S max low gw ] where P is the maximum or potential percolation out of the lower groundwater layer and S is the maximum or current storage in the lower groundwater layer. The above methodology has been used to generate projected soil moisture accounting parameter graphs for the projected period 2041-2050 for soil evapotranspiration, canopy overflow, canopy evapotranspiration and soil infiltration of the Ajoy river catchment to provide a more precise and realistic water availability accounting. Results and Discussion The Hydrologic Simulation Package HEC-HMS has been used to evaluate the effect of climate change on water scenario in the Ajoy Basin. The program computes direct runoff by using both traditional empirical Unit Hydrograph Model, and conceptual Model (Kinematic Wave Model). The model input requirement includes rainfall, soil condition and other hydrometeorological data. Evapotranspiration is calculated using the Thornwaite Method. Daily rainfall data and streamflow data for a period of five years (1997-2001) were used for the calibration and validation of the model. Fig 2 illustrates the fact that run off volumes of simulated and that of observed discharge during years 1998 to 2000 match well.   Fig 2. Simulated and Observed Hydrograph at Natunhat 1998-2000 In order to assess the future water availability scenario various soil water relationships like, canopy overflow, soil infiltration and soil ET were studied. Fig. 3 displays the various trends of soil moisture properties during 2041 – 50. Soil ET, Canopy ET and Canopy Overflow are seen to increase whereas Soil Infiltration decreases.    Fig 3. Projected soil moisture properties for Natunhat over the years 2041-2050    Fig.4a. Projected Flow Figures for Natunhat Sub Catchment from June to October 2041-2043    Fig.4b. Projected Flow Figures for Natunhat Sub Catchment from June to October 2044-2046    Fig.4c. Projected Flow Figures for Natunhat Sub Catchment from June to October 2047-2049  Fig.4d. Projected Flow Figures for Natunhat Sub Catchment from June to October 2050 Conclusion The importance of the inclusion of Soil Moisture Properties in the evaluation of future water availability is demonstrated in this study. It is the variation of properties such as soil ET, soil infiltration, canopy ET and its overflow over 2041-50 which have proved to have a considerable control over the future water availability scenario as illustrated in Fig 3. Over the years 2041-50 the soil evapotranspiration is seen to decrease, whereas the soil infiltration, canopy overflow and canopy evapotranspiration are seen to display increasing trendline. The stream flow and its peak, are seen to display decreasing trends from 2041-50,the reduction in the water availability can be attributed to the decrease in the number of rainy days coupled with increasing demand in agricultural, industrial and domestic sector. Acknowledgement Authors sincerely acknowledge the kind assistance, rendered in the form of data and all kinds of secondary information by the officials and personnel of the Damodar Valley Corporation, India Metrological Department, Central Water Commission and All India Soil and Land Use Survey . The future projection of stream flow hydrograph at Natunhat site was performed using the projected rainfall data for the period 2041-2050, provided by IITM, Pune. References
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