Viability for Minor Irrigation Tanks Cascade System Using Remote ..... HYDROLOGICAL VIABILITY ANALYSIS FOR MINOR IRRIGATION TANKS CASCADE SYSTEM USING REMOTE SENSING AND GIS

Many of the Andhra Pradesh minor irrigation tanks are inter-connected cascades, allowing surplus flow of the upstream tanks and return flow from the upstream command area to reach straight away downstream tank. To increase the irrigation supply in downstream of command area, irrigation tanks are being used. There are several troubles of the irrigation tanks, such as reduction of design discharge as a result of silting of channel and tanks, deterioration of stone masonry channel, and encroachment of drainage courses and tank water spread leads to the decline of tank performance. Water Resources Department (WRD) is implementing Andhra Pradesh Integrated Irrigation and Agriculture Transformation Project (APIIATP) for improvement and management of minor irrigation tanks through community based approach with the funding of World Bank .The prediction of water availability in tank is important for the purpose of improving productive use of the water resources in a tank cascade system. The land use/land cover map was prepared using LISS-IV imagery. The drainage courses problems are identified in the tank cascade system by SOI 1: 50,000 scale toposheet & satellite image. The problems were found in the earthen channel, catchments and head works. For the identified problems, the remedial measures are suggested for improving the tank cascade system to restore it to its original condition.


Introduction
Tanks are traditional irrigation structures commonly situated in many parts of Indian subcontinent to capture monsoon runoff. A tank comprises the catchment area, feeder channels; water spread area, outlet structures (sluices), flood disposal structures (surplus weir) and command area. It is reported that more than 70 -80 per cent of minor irrigation tanks need renovation to restore them for normal functioning.
Tank Rehabilitation / Restoration / Renovation is termed as " the tanks which are dysfunctional are brought to normal functioning by way of undertaking works on breach closing, tank bund strengthening and repairs or reconstruction to sluices and weirs". Many tanks are found in the form of cascades, which is defined as a series of small and medium tanks that are connected at successive locations down in one single common water course (Madduma Bandara, 1985;Panabokke, 1999). These tanks are hydrogeologically and socio-economically interlinked in terms of storing, conveying and utilising water.
If the hydrology of one or few tanks is altered by increasing either storage capacity through rehabilitation programmes or command area by developing new paddy lands, the entire cascade hydrology changes (Sakthivadivel et al., 1996).
Such changes can also have a socio-economic impact on the surrounding communities dependent on the water availability of the system. Therefore, it is important to take the total tank cascade system rather than an individual tank into account when planning, development and operations of small tank systems are considered. Levine (1996) analyses the fundamental reasons for the need to improve irrigation systems. He points out that the need for rehabilitation arises because of failures to adequately maintain irrigation systems. This problem is endemic throughout the world, but especially in the developing countries, due to severe constraints on the financial resources available for operation and maintenance. Many

Study Area
The study area covers Kavali mandal, North Latitude (Figure 1). Development, Vol.37, No. (2), April-June:2018 In this study, IRS-ID LISS-IV satellite data of 2016 have been used. The details are given in Table 1. In addition, SOI 57 N/13 toposheet of

Methodology
The toposheet 57 N 13 is collected from the Survey of India and is digitized and then the study area is delineated in QGIS software. Further, the more tanks which are connected in a cascade manner are delineated, its catchment ( Figure 3).
The catchment of each tank is also delineated besides water spread area and number of inlet channels.

Drainage
The surface drainage delineation is important to assess the hydrology of an area. Initially, rainfall received is absorbed by the soil and once it gets saturated it goes out as surface runoff. The surface runoff varies with surface conditions namely length and degree of slope, raggedness, soil texture and structure, cover conditions and lithology of the terrain. Every geographical area has a defined drainage system/ pattern that determines the groundwater potential (Gurtz, J.; Zappa, M.; Jasper, K).   (Table 2) and these are shown in Figure 4.

Surface Runoff Estimation
Rainfall -Runoff modelling is an essential part in water resources planning and management. The soil conservation service curve number (SCS-CN) is a simulation model that analyses runoff volumes from the rainfall. It is one of the efficient methods to estimate direct runoff volume in unguaged catchments (Hawkins, 1993;McCuen, 2002;Michel et al., 2005;Ponce and Hawkins, 1996). It uses the curve number (CN) to determine the runoff volumes.  formulae of the SCS method adopted for the current study is given in Figure 5.

SCS -Curve Method
The basic hypotheses of SCS method are: a. Runoff starts after the primary abstraction, Ia, has been contented b.
The ratio of real preservation of rainfall to possible maximum retention(S) is equal to the ratio straight runoff to rainfall minus initial abstraction.
c. The first concept Ia is linked to S as Ia = aS with the value of a being a function of antecedent moisture condition (AMC) and type of soil. The association between runoff depth Q (in mm) and rainfall P (in mm) in a rainfall event in the catchment AMC type 5 days total rain in previous season Dormant Growing 1 13 mm less than 36 mm less than 2 13 to 28 mm 36 to 53 mm 3 28 mm more than 53 mm more than   Journal of Rural Development, Vol.37, No. (2), April-June:2018 Graph: Kavali Big Tank -Monsoon rainfall and runoff (mm) 75% yield in mm -188.73 75% yield in mcft -247.04 Graph: Madhurapadu Tank -Monsoon rainfall and runoff (mm) 75% yield in mm -233.61 75% yield in mcft -64.95

Results and Discussion
The objective of the study is to map the land use/land cover of the study area, to have detailed information on the spatial variation to identify the problems in the drainage course of the tank cascade system through GPS survey and to suggest suitable analysis to measure the base data.
The minor irrigation tank system components consist of drainage course, catchments, tank bund, sluice and surplus weir locations. The problems identified are excessive Journal of Rural Development, Vol.37, No. (2), April-June:2018 weed growth-choaking of sections of canal, thereby reducing the velocity of flow and causing the deposition of sediment, silt accumulation, aquatic weed growth in water submerged areas is a problem because some of this growth eventually reaches the canals.
Total curve number was assigned using the unique land use and hydrological soil group.

Conclusion
To meet the water demand in Ayacut area, improved irrigation system with proper maintenance is required to increase agriculture production and rising environmental concerns.
Changing institutions and management within irrigation systems are now viewed as a catchment area and tank improvement process. This study is conducted towards hydrological viability of minor irrigation tank system. It was found that most of the irrigation tanks do not receive the surplus water from the upstream tanks. Through rainfall, runoff and GIS tracking over the drainage course and tank system, the problems were identified and suitable remedial measures were suggested for augmenting more water to the tank cascade hydrologic system. For optimum utilisation of financial resources it is suggested to receive and Journal of Rural Development,Vol.37,No. (2), April-June:2018 restore only those tanks that are hydrologically viable.Hence it is recommended that the rehabilitation of irrigation tank system is very essential. In this study, the and GIS and GPS are proved to be the most effective tools in discerning tank cascade water system.