Many large-scale irrigation systems, originally planned only for irrigation supply, are de facto multiple-use systems, which deliver water also for bathing, laundry, livestock watering, fisheries and other environmental functions. The importance of non-irrigation uses to the livelihoods of the rural poor has generally been ignored both in planning and operating these systems. An improved understanding of competition and complementarity of all water demands is essential for effective multiple-use management. This paper focuses in detail on one particular non-consumptive use: fish farming. The underlying objective is to explore the potential for, and constraints to, introducing cage-based aquaculture as a small enterprise for poor people (including landless households) living close to irrigation canals. A case study of Lower Bhavani Project in Tamil Nadu, India, provides evidence of technical constraints and challenges for irrigation engineers.

Good groundwater quality is essential for crop yield, soil productivity and environmental protection. Suitability of groundwater for irrigation purposes is determined by its geochemistry. Groundwater geochemistry explains links between chemical composition of groundwater and subsurface geological and non-geological pollutants. Subsurface rock formations control the composition of soil and hence that of water and vegetation. The ground water samples were analyzed for physico-chemical parameters like Electrical Conductivity (EC), Hydrogen ion concentration (pH), Bicarbonate (HCO3-), Calcium (Ca2+), Magnesium (Mg2+), Sodium (Na+), Potassium (K+), Sulphate (SO42-), Nitrate (NO3-), and Chloride (Cl-). Inverse distance weighted method of the Geographical Information Systems is used to prepare the distribution map of physio-chemical parameters of groundwater while overlay method is used to assess spatial, temporal changes and prepare groundwater quality zones of Walayar watershed in Parambikulam-Aliyar-Palar basin situated in Coimbatore district, Tamil Nadu, India. The results of study show that the quality of groundwater varies both spatially and temporally in Walayar watershed. The groundwater samples in some of the wells showed deviation from water quality standards indicating groundwater contamination. Hence, proper care must be taken to avoid any contamination of groundwater and its quality be monitored periodically.

CTo assess the quality of ground water and its suitability for irrigation, a study was carried out during pre and post monsoon seasons of 2006-2007. In the present study, the ground water samples from open wells, bore wells and dug cum bore wells were collected in the Noyyal river basin that encompasses the urban and industrial stretch of Tirupur. The values of EC ranged from 0.41 to 15.95 dSm-1 and pH ranged from 7.61 to 8.61. Sodium dominated among the cations and chloride among the anions. The sequence of cations found to be Na + >Mg 2+ >Ca 2+ >K + and anions followed the sequence of Cl - > SO 4 2- >HCO 3 - >CO 3 2- . Salinity and sodicity classes were assessed as per Richards (1969). Very high salinity category (C4) dominated (56.90 per cent) and low sodium (S 1 class) (74.14 per cent) category recorded the major classes of salinity and sodicity respectively. Residual sodium carbonate and Residual Sodium Bicarbonate content classified under satisfactory with 68.9 per cent (<1.25 m.e L -1 ) and 87.93 per cent (<5 m.e L-1 ) respectively. Classification of the samples based on salinity and SAR indicated that 68.97 per cent of samples did not pose infiltration problem to the soils and 31.03 per cent will result in slight to moderate infiltration due to irrigation. It was found that 50 per cent of samples having slight to moderate (0.7 t0 3.0 dSm -1 ) salinity problem followed by 43.01 per cent under severe salinity (>3.0 dSm-1 ). Sodium and chloride toxicity were found in majority of the samples. Slight to moderate toxicity of sodium (SAR>9) was recorded by 67.24 per cent of samples which may cause accumulation of sodium over a long period.

To assess the ground water quality and its suitability for irrigation, a study was carried out during April and June 2010 in Parambikulam Aliyar Basin, Tamil Nadu. Ground water samples were collected from open wells, bore wells and dug cum bore wells in the Parambikulam Aliyar Basin and their quality parameters were assessed. pH values ranged from 6.6 to 8.6; electrical conductivity values were ranged from 0.29 to 6.80 dSm -1 and most of the samples were under medium salinity class (C 2 ) (48.57%). Calcium, magnesium, sodium and potassium content ranged from 0.40 to 13.36 m.e L -1 , 1.04 to 26.16 m.e L-1 , 0.80 to 25.48 m.e L -1 and 0.05 to 2.52 m.e L -1 respectively. Most of the samples were found to be magnesium dominating and magnesium exceeds the calcium content in most of the water samples both during April and June 2010. Magnesium toxicity will be exhibited in continuous use of water to crops. Carbonates, bicarbonates, chloride and sulphate concentration varied from 0.0 to 4.00 m.e L -1 , 0.80 to 12.80 m.e L -1 , 1.20 to 45.20 m.e L -1 and 0.02 to 7.97 m.e L -1 respectively. The sequence of cations were found in the order of Na + >Mg 2+ >Ca 2+ >K + and anions followed the sequence of Cl - > SO 4 2- >HCO 3 - >CO 3 2-. Total hardness in the study area varied from 6.26 to 140.66 m.e L -1 . Most of the samples were deficient of Ca and Mg category during both the seasons. RSC values varied from 33.12 to 8.56 meL -1 and most of the samples are coming under safe category (71.43% - 80.0 %). Residual sodium bicarbonates also come under safe category. SAR values ranged from 0.49 to 13.21 and all the samples were found to be low sodium category (S 1 ). There is no sodicity problem exist among the irrigation waters. In the present study, Permeability Index ranged from 26.49 to 101.59 and majority of the samples exhibited that there is no permeability hazard.

Ground water resources diminish at alarming rates in hard rock regions as it is the primary source of irrigation as well as domestic purpose. Periodic replenishment of ground water in these areas is only through rainfall. Delineation of potential groundwater recharge zones in hard rock areas is of vital importance to enhance the recharge. Conventionally, suitable zone for groundwater recharge is deciphered using hydrogeological, geophysical and geomorphological maps, which is often time consuming and uneconomical. But, the analysis of unconfined aquifer response in terms of rise in water level due to precipitation in hard rock areas is one of the rapid and cost-effective methods. Cross-correlation of rise in water level and precipitation is established for Parambikulam-Aliyar-Palar (PAP) basin of TamilNadu, India to delineate groundwater recharge zones. The entire area is classified into various recharge zones depending on coefficient of correlation. Thus, decisions on construction of recharge structures / optimal pumping in these areas can be decided for sustainable ground water resource management to meet future demands.