The present study aims to detect the trends in annual and seasonal rainfall and its magnitude in Amaravathi basin, Tamil Nadu. In this study, the mean annual and seasonal rainfall in 10 rain gauge stations of Amaravathi basin have been analysed to determine the trend and its magnitude for the period of 1982-2014. The trend analysis is done using Mann-Kendall and Sen’s slope estimator. The trend analysis results showed wide variations during all the seasons. The increasing trend of rainfall is found to be dominant during north-east monsoon season when compared to other seasons.
Amaravathy river is one among the main tributaries of the river Cauvery and is surrounded by four districts viz., Coimbatore, Dindigul, Karur and Tirupur in Tamil Nadu. In Karur district 9 out of 15 blocks is over-exploited, 5 is semi-critical and one is under critical category. Coimbatore district has 6 blocks under over exploited category of the 12 blocks, 4 under semi-critical and 2 under safe category. While in Dindigul district out of the 14 blocks 11 is under exploited 2 is semi-critical and only one block is under safe category. Tirupur district is having 2 blocks AbstractIntegration of remote sensing and geographical information system (GIS) has become a breakthrough in the field of groundwater studies. The demand for water is increasing exponentially each year showing an increase in dependence on groundwater sources as surface water sources are no longer satisfying the demand. The present study attempts to identify the potential recharge zones and locations for artificial recharge structures in Amaravathy Basin, Tamil Nadu. Weighted overlay analysis tool in Arc GIS application is used to identify the areas. The input data for this analysis are different layers like geology, geomorphology, soil, rainfall, land use-land cover, soil lineament density and drainage density. The result depicted the groundwater potential zones into four categories, viz., good, moderate, low and poor that and can be used for better planning and management of groundwater resources. Various groundwater recharge structures like boulder dams, check dams, percolation tanks, recharge pits etc., were suggested in appropriate locations of Amaravathy basin according to the derived results.
Drought tends to be a creeping phenomenon occurs gradually with the deficiency in rainfall further extending its impact on sectors which are dependent on water. The drought characteristics were analysed in Parambikulam Aliyar Project (PAP) basin based on the European Centre for Medium range Weather Forecasts Interim Reanalysis (ERA-Interim) gridded data with resolution of 0.125° ×0.125° during 1981-2017. Reconnaissance Drought Index (RDI) was applied for monitoring the drought. The variables used in RDI are rainfall and potential evapotranspiration (ETo), the required meteorological data were taken from the ERA Interim dataset and ETo was calculated using Penman-Monteith method. RDI indicated that 41% of the time had drought condition over 37 years. Two years (1982 and 2012) faced severe drought across all the parts of the PAP basin and the highest number of mild drought events were observed than the other drought conditions in PAP basin. Results showed that Plain areas in PAP basin experienced maximum number of drought events compared to the other areas in PAP basin during the investigation period.
SUMMARY :The total water resources available in India are 1859 km 3 , which is roughly 4 per cent of the world's fresh water resources. Tamil Nadu accounts for 4 per cent of the land area and 6 per cent of the population, but only 3 per cent of the water resources of the country. Most of Tamil Nadu is located in the rain shadow region of the Western Ghats and hence receives limited rainfall from the South-west monsoon. The demand for water in Tamil Nadu is increasing at a fast rate both due to increasing population and also due to larger per capita needs triggered by economic growth. The annual per capita water availability in India is about 2200 m 3 whereas it is only 750 m 3 in Tamil Nadu. As per World standards our State is under water scarcity.Groundwater is the most important water resource on earth. It comprises of the major and the preferred source of drinking water in rural as well as urban areas and caters to 80% of the total drinking water requirement and 50% of the agricultural requirement in rural India. The groundwater is a dynamic and replenishable natural resource, but in hard rock terrains its availability is of limited extent and is essentially confined to the fractured and weathered horizons. In Tamil Nadu, more than 70% of the geological formation is of hard rocks which limit the availability and extraction of ground water unlike other formations. Research studies by various institutions reveal that the percentage of safe blocks has declined from 35.6 per cent to 25.2 per cent while the semi-critical blocks have gone up by a similar percentage. Over-exploitation is occurring in more than a third of the blocks (35.8 %) while eight blocks (2 %) have turned saline over the past five years in Tamil Nadu. Henceadoption of groundwater resource developmental activities are compulsoryto handle as well as to meet out the demand in future. And also adoption of improved technologies like micro irrigation,System of Rice Intensification (SRI) and Alternate wetting and drying can greatly reduce the water requirement which also increases the yield.
Inadequate natural drainage facilities and flat lands causes, some of the Cauvery river basin command are suffering waterlogging and alkalinity problems during the canal water supply and period of excess rainfall. Subsurface drainage system is the method to lower the depth to groundwater level below the root zone and creates a favorable environment for crop growth. A study aimed to evaluate the performance of the parallel pipe subsurface system installed in farmers’ field at Sembari village, Lalgudi Taluk, Trichy District, Tamil Nadu in a waterlogged paddy field from October 2020 to February 2021. The field experiment was conducted with the combination of three lateral drain spacing (7.5, 10.0 and 12.5 m) and two drain depths (60 and 80 cm). 63 mm PVC perforated pipes wrapped with coir envelope were laid as lateral drains at a grade 0.3%. Inspection chambers connected with collector drains laid at a grade of 0.6% were used to measure the drain water discharge, observation wells installed midway between lateral pipes drains were used for measuring the depth to groundwater level. Hydraulic properties of soil, depth to water level, discharge collected in drain pipe were used as evaluation parameters. This study revealed that soil hydraulic conductivity had been increased to 30%, pH, EC and ESP has been reduced to 12, 54 and 20%, respectively. The system has performed well to alleviate the waterlogged condition in 7.5 m lateral drain spacing and 80 cm drain depth treatment by observing the higher rate of decrease in depth to water of 0.3 to 0.4 m and a drainage coefficient of 0.069 to 0.29 cm/day.
The temporal behavior of precipitation is more important in crop planning and prediction of extreme events. Salem District is one of the land-protected districts in Tamil Nadu. The main objectives of this study is to describe the temporal patterns of rainfall amount and concentration of Salem District. The rainfall data for various locations and at different course of time were collected from Indian Meteorological Department (IMD) and analyzed to study the variability of rainfall in Salem district. It receives rainfall under influence of both southwest and northeast monsoons. It was observed that the maximum rainfall in the district was recorded in 2005 (1375 mm) and the minimum rainfall was recorded in 1980 (51 mm). It was also observed from the annual rainfall plot that the rainfall in the district is uneven. The overall average annual rainfall of the district over the years is around 81 mm. The maximum number of rainy days was recorded in 2010 (91 days). The station wise average rainfall analysis showed that that the Yercadu station has recorded the highest average annual rainfall of1223.16mm compared to the other stations. The major contribution of rainfall to the district is from the South-west monsoon, which is about 42%, followed by the northeast, which is 38%. On an average, the north-east monsoon contributed a maximum of 306 mm to the total rainfall in the district and the minimum rainfall was recorded during the winter season. Between 1977 and 2012, the maximum rainfall was observed in 2005 (1375. mm) which has its highest contribution from the northeast monsoon. In addition, the highest record of northeast monsoon had been recorded in 2005 (712 mm). Around 20 years, the rainfall is lesser compared to the average annual rainfall (812 mm).Hence, the district has not experienced any major distress with respect to rainfall as majority of years fall under normal category. This temporal variability analysis of rainfall in the district helps in crop planning and proposing water conservation activities.
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