Search

Sills and baffles are appurtenances used to stabilize hydraulic jump in a stilling basin. The force acting on these appurtenances are characterized by the drag coefficient (CD). This paper describes experimental methods carried out in a rectangular channel to analyze the drag characteristics of sill and baffles in free (unsubmerged) and submerged hydraulic jumps. The sills and baffles were designed as per the USBR type III stilling basin guidelines. A calibrated loadcell connected to an Arduino board was used to measure the drag force. Errors in measurements are limited to 1%. The drag co-efficient was obtained for different Froude numbers (F1=U1/√gy1) pertaining to strong jump (4.5–9) for different relative position of sills (xS/y2) and baffles (xb/y2) from the nozzle of the sluice gate. Both forced (unsubmerged) and submerged jumps were investigated. It is seen that the drag coefficient of appurtenances in submerged jumps were lower than those in free jumps. This may be attributed to the reduction in wake size in submerged jumps. Comparisons of the experimental results of the sill with the previous theoretical studies are reasonable. [ABSTRACT FROM AUTHOR]

Sustainable use of the available water resource is an important challenge for food security. An irrigation canal system consists of a number of pools connected to each other by control structures. Unsteady flow Saint-Venant equations are used to model the flow in the canal system and these equations are solved using implicit finite difference methods. The canal system is represented as linear time invariant system and the resulting equations are the dynamic equations in state space form. These linearized equations are modelled in Matlab® environment. The control strategy adopted in this research is the downstream control method of operation and the control structures adopted are radial gates and modified radial gates. The unsteady flow model is applied to the chosen study area and the results obtained from the model are used to simulate the dynamics of the canal system using model predictive controller toolbox. The results show that any closed loop controller will work efficiently with the hydraulic model developed. [ABSTRACT FROM AUTHOR]

The impact of untreated effluent from dye industries and domestic sewage that are discharged into the irrigation tank in Pandravedu village in South India was assessed through physico-chemical analysis of water samples and focus group discussion with the community. Thirty-six samples were collected from the study area across three seasons and analysed in the laboratory. The irrigation water quality indices computed indicated that the levels of sodium, salinity and hardness exceeded the permissible limits of irrigation standards. Consequently, rice yield had reduced by 40% in the region, thereby affecting the livelihood of the farmers. The colour of fishes in the tank also changed and their consumption contributed to health-related issues in the village. [ABSTRACT FROM AUTHOR]

Research on the effect of climate variability/climate change on runoff is limited in humid tropical regions. Climate change has implications beyond the water resources sector, such as effects on agriculture and fisheries. Hence, such studies are becoming increasingly important. This study uses both historical field data and future climate forecasts from General Circulation Model Hadley Centre Coupled Model, version 3 GCM HadCM3. These data are further downscaled using third generation of the Hadley Centre's regional climate model (HadRM3), with Providing REgional Climates for Impacts Studies (PRECIS) software under the three Quantifying Uncertainties in Model Projections (QUMPs) with a horizontal resolution of 25 km X 25 km by the Centre for Climate Change and Adaptation Research, Anna University Chennai, for the state of Tamil Nadu. These downscaled data are used to study runoff changes due to climate change for the Kosasthaliyar sub-basin in South India. A trend analysis of the hydro-meteorological data for the sub-basin indicates that future rainfall is expected to decrease by approximately 10%, while the mean temperatures will increase by the year 2100. The runoff changes from 2011 to 2040 are not perceptible when compared to the historical period of 1971 to 2000. This study attempts to provide information on climate variability and its impacts on runoff in the Kosasthaliyar sub-basin. [ABSTRACT FROM AUTHOR]

Sills and other appurtenances are often used to aid the formation of a hydraulic jump in a stilling basin. The drag force acting on a sill in forced hydraulic jump depends on the initial Froude number F1, the height of the sill S, and its distance xs, measured from the toe of the jump. The forward flow in the main body of the hydraulic jump behaves like a wall jet. Therefore, based on observed data, simple relationships were developed to predict the maximum velocity Um and the half-width b of a free hydraulic jump. These are coupled with a dynamic pressure model that expresses the local drag coefficient Cdδ of a sill in a plane turbulent wall jet. The drag coefficient for the sill in a forced hydraulic jump Cd was obtained by a simple transformation involving the wall jet parameters. [ABSTRACT FROM AUTHOR]

Radial gates are widely used to control the flow in irrigation channels and spillways. Radial gates require lower hoisting force and have better discharge characteristics in partial gate openings. The accurate discharge measurement through a radial gate is a challenging problem especially in submerged flow conditions. The coefficient of contraction Cc is an important parameter for accurate discharge measurement in open channels. In this study, an attempt has been made to determine the coefficient of contractionCc and velocity coefficient Cv for radial gates both for free flow and submerged flow conditions. The flow emanating from a gate is similar to the wall jet emerging from a nozzle. The Cc and Cv values under free and submerged flow conditions are obtained from the measured jet velocity and the discharge. The coefficient of discharge values under submerged flow conditions show large variations with submergence and hence discharge characteristics needs to be improved for better control of flow. Hence, experiments are conducted so as to improve the discharge characteristics by modifying the exit geometry of the radial gate by attaching a quarter of an elliptical lip. Three different geometries of elliptical lips were attempted and the results show reasonable increase in the contraction coefficient. [ABSTRACT FROM AUTHOR]

Flooding is one of the most disastrous global hazards, which has been occurring more frequently in recent times. It is observed that climate change is likely to increase the intensity and the frequency of floods and river basins have become more vulnerable to fluvial flooding. In this study, the impact of climate change on fluvial flooding was analyzed over the Adyar sub-basin. This study applied statistically downscaled Global Climate Model (GCM) data in a CMIP5 dataset of IPCC Assessment Report 5 (AR5). Based on the performance to simulate the observed climate, four GCMs, namely, cesm1-cam5, mpi-esm-mr, ncar-ccsm4, and bnu-esm, for RCP 4.5 were selected for projections of the future scenario. The Intensity-Duration-Frequency (IDF) curves for the past and future scenarios were derived from the IMD-observed and GCM-projected rainfall data. Integrated flood modeling was performed with hydrologic (HEC-HMS) and hydraulic (HEC-RAS) models. Finally, in order to visualize the inundation areas according to the future climate projection, flood inundation maps were prepared geospatially using the ArcGIS software. For the 100-year return period, the results predict that the peak discharge for the future climate scenario would increase by 34.3%–91.9% as compared to the present climate scenario. Similarly, the future projections show an increase in the flooded area ranging from 12.6% to 26.4% based on GCMs. This simulation helps in understanding the flood risk over the Adyar sub-basin under the changing climate and the requirement for the regulation of developmental activities over the flood-prone areas. [ABSTRACT FROM AUTHOR]