Flood Moderation & Water Management Study in a Non-Himalayan Indian Basin

India is one of the very few countries in the world endowed with substantial land and water resources. Being a country with predominantly monsoon climate, the rainfall is erratic, unevenly distributed in space, time and hence droughts in some parts/seasons and floods in some other parts/seasons frequently occur. Sometimes, both of them also occur simultaneously. In order to reduce the adverse impacts of floods and droughts, intra-basin surface/subsurface water management followed by inter-basin subsurface & surface water transfer is proposed to ensure water availability within the basin first, followed by transfer of basin excess water, preferably to the adjacent basin (s) within the region -having water storage capability during the regional floods, purely on a short term basis. In the present study, a sub-catchment of Subarnarekha Basin has been considered as the study area. This study focuses on the proposal of Intra-basin/Inter-basin subsurface/surface storage/transfer during a portion of the flood period. This is accomplished after creating some Intra-basin storage, by analyzing 13 years of daily discharge data -starting from 2004, for the Jamsholaghat Gauge-Discharge (G-D) site in the basin. Thus, all the four purposes -in their order of preference, viz., 1) moderation of basin flood peak; 2) creation of intrabasin surface/subsurface storage; 3) groundwater recharge and 4) short term mitigation of water scarcity in the neighboring basin (s), are expected to be achieved through this proposal.


Introduction
On the Earth's surface, the freshwater availability generally depends on the hydrological cycle. If the technologies such as desalination of sea water are used extensively, then it would further increase the availability of freshwater [1]. Due to increase in the global population and change in the climate conditions, there will be increases in the demand of freshwater which may lead to shortage of water resources spatially and/or temporally. Hence, proper planning is needed for judicious water utilization -for striking balance between demand and supply, supply and utilization at global/regional/local scales for ensuring sustained availability of water. Here, the concept of basin water management and Inter-basin water transfer or river interlinking comes into picture. India is a large developing country and keeping its population growth in mind, India is expected to face severe water shortages in the near future. Climatic and geographic variability causing the drought conditions results in the suffering of humans/animals in different regions of India. Droughts cause water shortage mainly for domestic, agricultural and industrial purposes. The proposal for interlinking of rivers (ILR) of India is on the wish list of many stakeholders in order to reduce the negative impacts of droughts in some regions by utilizing the simultaneously prevailing excess flood waters in some other regions.

Literature Review
Literatures have been reviewed from 1990 to 2017, out of which few literature reviews have been shown in brief. Rao former irrigation minister of India showed his concern towards the shortage of water in future and he proposed the linking of river is one of the possible way to overcome from this shortage [2]. Since then many researches, proposals, plans and actions have been carried out in order to overcome the shortage of water for future generation [3][4][5].
Bhaduri and Bharbier presented a study on the inter-basin water transfer proposed for India through an Ex-ante based analysis of the water transferred between the surplus and deficit basins. Ex-ante analysis has been used, in order to get an idea of the price movement or the impact of newly adopted policies on the future [6].
Bonkile and Pajgade presented a study showing the different methods and techniques, all the possibilities of past work those are being used in order to transfer the surface water in case of inter-basin and intra-basin [7].
George et al. highlighted the concept of Inter-basin water transfer along with their resulting problems and economic/ecological benefits, which may lead to a sustainable development of that region [8].
Gupta and Zaag presented a study by considering the interbasin surface water transfer as a part of integrated water resource management. The authors considers all the criteria proposed by international commissions, scientists in order to access whether this transfer falls under the integrated water resource management or not [9].
Hamaideh et al. presented an experimental study on Wadi Ishe in Jordan to show the effect of an artificial groundwater recharge technique (viz., recharge of surface runoff and to store that water in an artificial groundwater reservoir) to reduce the loss due to evaporation and an alternative of water supply for rural areas [10].
Mahabaleshwara and Nagabhushan highlighted on interlinking of river as an agenda by considering the shortage of water due to the current trend of precipitation and the would ultimately cause shortage of surface water availability [11].
Pelkey presented an article on interlinking of river. The author has discussed in details regarding the California's state water project, its pumping cost, total lift and what are the problems associated with construction. The author also proposed the few potential canals as suggested by National Prospective Plans [12,13].
Verdhen presented a study to show the efforts made by the Madhya Pradesh state government in India, to preserve the people's hope at present and future towards water availability by developing intra-basin schemes and interlinking of subbasins (i.e., Deb-Goi Rivers in the district of Barwani) through sustainable studies [14].
Vyas et al. presented a study on the interlining concept by considering the five river basins of Rajasthan in India. Their proposal includes connecting the lower areas of Chambal basin with the lower areas of Banas, Gambhir, Banganga and Parbati basins. The main reason behind this linking was to mitigate the flood situation in Chamal vicinity and also to mitigate the drought conditions in other four basins [15].
After reviewing the relevant literature, following gaps have been identified: 1) None of the literature reviewed so far have proposed any method for optimizing depth and cost of excavation in the link channels. 2) Surface link channels involves large land acquisition and associated problems like relief & rehabilitation. None of the studies -except one generic study, have so far have proposed any method to overcome this problem.
3) Identifying a particular basin as either a surplus basin or deficit basin is controversial and is also influenced by climate change as well as upstream unilateral Interbasin transfers, e.g., due to the unilateral diversion of the flow from Yarlung Tsangpo (i.e., Brahmaputra River) in the Tibetian autonomous region of China, the Brahmaputra River flowing through the NE India, can no longer be identified as a surplus basin. Due to climate change induced intense storms, many of the so called deficit basins are also affected by floods occasionally. Likewise, many of the 'Surplus basins' do get affected by continual/continuous water scarcity/drought conditions due to a general reduction in the number of rainy days and a long gap between two successive rainy days. However, there is no difference of opinion as far as utilizing the short term Inter-basin transfer especially during flood period, purely for the purpose of the flood moderation. 4) There is no provision for reversing the flow direction in the interlinking surface channels. Thus, it is not possible to ensure two-way Inter-basin surface water transfer between two neighboring basins. This forms a major limiting factor. 5) Since the basin or catchment or watershed is having a natural boundary, Intra-basin storage and transfer need to be given a higher priority than inter-basin transfer. This aspect appears to have been overlooked, in all the literature reviewed here.

Methodology
This chapter deals with the methodology involved in this study. It starts from the delineation of Jamsholaghat catchment area which is a sub-catchment of the Subarnarekha basin, for which ArcGIS software has been used. This was followed by an analysis of the daily Gauge-Discharge (G-D) data from 2004 to 2016 for Jamsholaghat G-D site in order to estimate the peak discharge and to analyze the various feasible flood management (FM) techniques [16]. It also includes the steps involved in selecting the suitable water harvesting structures.

Study Area
Study area involves the Jamsholaghat sub-catchment of the Subarnarekha Basin. The present study area extends over parts of the Eastern Indian states of Odisha and West Bengal, having a total area of 552 km 2 . It lies between 86°30' and 86°50' E longitudes as well as 22°04' and 22°32' N latitudes. The Subarnarekha and the Burhabalang form the major river systems in the sub-catchment. Length of the Subarnarekha River and Burhabalang River is 22.74 km and 44.32 km respectively [17]. Delineated DEM of study area in Subarnarekha Basin is shown in Figure 1.

Intra-basin Surface Storage
Intra-basin surface storage means making surface storage available within the basin itself. The existing facilities available are as follows: stream channels, drainage channels, surface depressions and flood plains. The volumes of these existing facilities have been estimated using a Geographic Information System (GIS) software. For estimation of volumes of stream channels, drainage channels and flood plains, approximated lengths and cross-sections of the channels have been used. For volume estimation of surface depressions, contour maps of 5m interval and topo-sheets of the study area have been used.
After estimating the volumes of stream channels, drainage channels, flood plains and surface depressions, additional flood volume could be created using subsurface dykes, relief wells and check dams. In the present work, relief wells have been used to create the additional flood storage volumes.

Intra-basin Surface Transfer
Intra-basin surface transfer means transferring the surplus water within the basin itself through existing drainage channels. The facilities available are stream channels and drainage channels. The volumes of these existing facilities have been estimated using a GIS software. For estimation of stream channel and drainage channel volumes, approximated lengths and cross-sections of channels have been used.
After estimating the surface channel and drainage channel volumes, additional flood storage volume could be created using diversion channels and other canals.

Inter-basin Subsurface Storage
Inter-basin subsurface storage means making subsurface storage available within a neighboring basin. In order to estimate the subsurface storage, lithological data is required. This data has been collected from Central Ground Water Board (CGWB), Bhubaneswar, Odisha, India [18]. Lithological data gives the details of different layers of soils/rocks available below the ground surface. Such data for 8 existing wells have been collected in order to estimate the subsurface storage. Depth details of the aquifers having 3 different layers for each Study in a Non-Himalayan Indian Basin of these 8 existing wells have been given in Table 2.   ii. Theim's Equation Assumptions: a) Subsurface flow is fully laminar and flow direction in the vicinity of wells is radial. b) Soil is saturated and homogeneous. c) Darcy's Law is valid. For confined aquifer (s), discharge is estimated using Equation 1 and for the unconfined aquifer, discharge formula is given by Equation 2 [20]. As the storm duration for the historical peak flood of Sept. 2011 is 10.8 days, it could be possible to select a number of relief wells based on the entire volume -corresponding to Inter-basin subsurface storage as given in Table 4. Here, the historical peak flood hydrograph has been partitioned into different time periods as shown in Figure 3 and volumes corresponding to Inter-basin subsurface storage for different scenarios have been estimated.

Inter-basin Subsurface Transfer
Inter-basin subsurface transfer means transferring the surplus flood volume to the neighboring basin (s) through subsurface conduits. Existing facilities available are the interconnected and unconnected aquifers. In the present work, surplus flood volume is proposed to be transferred using subsurface conduits and relief wells (RWs).
A typical case of a 2-directional flow (i.e., water can be transferred from the left RW1 to the right RW3 as well as from the right RW3 to the left RW1) through subsurface conduit (s), as shown in Figure 4. There are two possible cases arising due to 2-directional flow.
Case 1 -For flow towards Relief Well (RW) -1: The steps involved are as follows: a) Valves V 2A , V 2B and V 1C need to be closed. b) Valves V 1A , V 1B and V 2C need to be opened. c) Pump (P 1 ) needs to be operated and Pump (P 2 ) needs to be kept idle. *Depth to be provided depends upon soil profile A typical sketch of the flow towards Relief Well (RW) -1 has been shown in Figure 5.

Inter-basin Surface Storage
Inter-basin surface storage means making the surface storage available within a neighboring basin. The existing facilities available are as follows: stream channels, drainage channels, surface depressions and flood plains. The volumes of these existing facilities have been estimated using ArcGIS software. For estimation of stream channel volumes, drainage channel volumes and flood plain volumes, approximate lengths and cross-sections of the channels have been used. For estimation of surface depression volumes, contour maps of 5m interval have been used.
After estimating the volumes of surface channels, drainage channels, flood plains and surface depressions, additional inter-basin surface storage could be created using subsurface dykes, relief wells and check dams.

Inter-basin Surface Transfer:
Inter-basin surface transfer means transferring the surplus flood water to neighboring basin. The facilities available are stream channels and drainage channels. The volumes of these existing facilities have been estimated using a GIS software. For estimation of stream channel volumes and drainage channel volumes, approximated lengths and cross-sections of the channels have been used.
After estimating the surface channel and drainage channel volumes, additional inter-basin surface transfer capacity could be created using diversion channels and canals. In the present study, some additional flood volume is proposed to be transferred as indicated in Table 11.

Flood Management (FM) Scenario
Hydrographs corresponding to four FM scenarios have been shown in Figures 7 to 10. Discharge and volume corresponding to four FM scenarios have been shown in Table 3 and Table 4 respectively.

Inter-basin Subsurface Storage
Discharge through each aquifer layer of the existing wells have been estimated using Theim's equation for both the unconfined aquifer and confined aquifer (s) as shown in Table 5. After applying the continuity equation, inter-basin subsurface recharge through each of the existing wells have been estimated and are shown in Table 6. For the existing well details, refer to Table 2. As the historical peak flood has a duration of 10.8 days, it would not be proper to select a number of relief wells based on the entire volume corresponding to inter-basin subsurface storage. Hence, the flood hydrograph considered here has been divided into different time periods and volumes corresponding to inter-basin subsurface storage for different scenarios have been estimated as shown in Table 7. Refer to Figure 4 for the legend for all the time period notations. In the table 7, T 3bs is inter basin subsurface transfer start time, T 3cs is inter basin surface storage start time, T 3ds is inter basin surface transfer start time, T p is peak discharge time, T 3de is inter basin surface transfer end time, T 3ce is inter basin surface storage end time, T 3be is inter basin subsurface transfer end time, T 3ai is inter basin subsurface storage intermediate time and T 3ae is inter basin subsurface storage end time.
Maximum volume corresponding to inter-basin subsurface storage for each of the FM scenario have been considered for further analysis. Based on the maximum volume, estimation of the required number of relief wells have been done. Recharge estimation through these proposed relief wells are shown in Table 8.    Inter-basin subsurface storage volume has been estimated as product of recharge and historical Peak Flood Duration. Interbasin subsurface storage volume estimation for all the FM scenarios have been shown in Table 9.

Intra-basin/Inter-basin Surface Storage/Transfer
Contour map of 5m interval, topo-sheets and drainage channels & stream channels of the study area have been shown in Figures 11 to 13. Estimation of existing surface storage and estimation of volume to be created have been shown in Tables 10  and 11 respectively.    In order to create the additional flood volume, relief wells are being proposed. Estimation of total recharge through proposed relief wells and estimated recharge volume for all the scenarios have been shown in Table 12 and Table 13. Locations of the proposed relief wells (PWs) around the Existing wells (EWs) have been shown in Figure 14.

Inter-basin Subsurface Transfer
Assumptions: As per the Bureau of Indian Standards (BIS) Code of Practice 4880 (1976), the cross-sectional average velocity (V) through the subsurface transfer conduits has been considered as 7.5 m/s and circular channel crosssections have been proposed [21]. Discharge formula is given by Equation 3.
Where, Q 3b is inter-basin subsurface transfer discharge, Q r is recharge, D is the diameter of subsurface conduit, V is the velocity and n is the number of subsurface conduits. The estimation of diameter and the number of subsurface conduits required to transfer the additional flood volume from Subarnarekha basin to Burhabalang basin through subsurface transfer conduits has been shown in      In the present study, relief wells and subsurface flow conduits have been used extensively as viable FM techniques. Relief wells may be substituted by check dams of suitable recharge and storage capacity.

Conclusions
In the detailed analysis of all the broad FM techniques along with the different FM scenarios have been carried out. The following conclusions are drawn, based on this study: a) Among the various FM techniques, topmost priority has been given to intra-basin storage/transfer techniques rather than the inter-basin storage/transfer techniques and within them high priority has been given to storage rather than transfer. b) In the historical peak flood hydrograph considered for different FM scenarios, various FM techniques have been proposed through horizontal lines, so as to make the operation simple and to ensure a steady discharge for a longer duration of time within the entire flood duration. c) Out of all the four FM scenarios considered and detailed in Table 1, FM scenario I is the best scenario for storage (69%) and the worst scenario for transfer (31%), whereas FM scenario IV is the best scenario for transfer (16%) and the worst scenario for storage (84%). d) In case of inter-basin subsurface transfer for different FM scenarios, the number and the diameter of the proposed subsurface conduits is ranging between 2 -3 and between 2.8 m to 3.1 m respectively. e) In case of inter-basin subsurface transfer for different FM scenarios, the subsurface conduits are proposed to be placed at a center to center spacing of 10m across the subsurface transfer direction. f) In case of intra-basin/inter-basin surface storage/transfer, some of the proposed relief wells may be substituted by check dams with suitable recharge and storage capacities.