National Institute of Hydrology

The study computes degree-day factor for snow and ice over the Dokriani glacier (4000 m altitude) in Garhwal Himalayas. The effect of natural dusting on degree-day factor is also examined. Information on the degree-day factor for snow and ice is required for the estimation of snow and ice melt runoff from a glacierized basin.

The report presents a detailed review of mathematical modeling of flows in alluvial streams. Various computer codes for this are presented and a model for simple-island case is prepared. Branched flows in open channels with alluvial conditions occur in natural and man-made systems. Analysis of such flows by mathematical modeling is important considering its applications in water resources and environmental engineering.

The report describes the software, which has been developed for flood control regulation of a system of reservoirs. The reservoirs can be gated or ungated, and the system can have any combination including weirs and diversions. For operation of reservoirs, the scenario has been divided into two categories depending on the reservoir level and inflows - normal operation and emergency operation.

The input data requirements of the software are modest. This software along with previously developed software for conservation operation would provide a complete set of tools to analyze any system configuration for the range of purposes for which reservoirs are commonly built in India.

The report deals with the procedures to estimate dispersion coefficient from exit concentration observed due to a step change in the concentration input. A simple method as well as an optimization method has been evolved and the application of the methods on published datasets discussed.

Dispersion occurs in many problems of groundwater flow, such as pollution from concentrated and distributed source, sea water intrusion, seepage of polluted surface water through rivers or lakes and changes in water quality due to artificial recharge. Application of the solution of advection-dispersion equation in soil media for prediction and forecasting of solute concentrations requires the estimate of coefficient of hydrodynamic dispersion, commonly known as ‘dispersion coefficient’.

In the study saltwater intrusion processes in a hypothetical homogenous and multi-layered coastal aquifer system are simulated using the United States Geological Survey (USGS) finite element model for saturated-unsaturated fluid density-dependent groundwater flow with energy transport of chemically reactive single species solute transport (SUTRA) for different boundary conditions and aquifer parameters.

The saltwater intrusion profiles for steady-state or transient conditions are obtained and analyzed. The effects of changes in the permeabilities of aquifers and aquitards, changes in the influx at the boundary, and changes in dispersivities in medium on the saltwater intrusion process are investigated.

The report summarizes aspects of the theory of anisotropic flow in porous media and reviews the methodology for computing hydraulic potentials in an unconfined aquifer system. An algorithm has been devised by applying appropriate transformation techniques for anisotropic domain.

Numerical experiments have been performed using the algorithm to compute hydraulic potentials in certain hypothetical anisotropic aquifer systems. A number of cases have been studied with different coefficients of anisotropy for the aquifer as well as the angle inclination of the bedding planes of the soil strata. The simulated hydraulic potentials in the anisotropic domain are established as equipotential lines in vertical sections.

The report uses the Soil Conservation Services (SCS, 1956), Curve Number (SCS-CN) method, a widely used event based rainfall-runoff method for simulating daily rainfall-runoff data of three catchments, viz., Ramganga and Hemavathi catchments of the sub-humid regions and Sabarmati catchment of the arid region of India.

In the model formulation, the daily variation of parameter, potential maximum retention is governed by the known antecedent moisture condition. Hydrologic simulation studies provide a useful and important input to water resources planning and watershed management practices.

The report discusses the water availability computations under different data availability scenarios. Water availability generally refers to the volume of water available from the basin or stream at a particular point over a specified period of time. Volumetric relationship is reflected between rainfall and runoff. Many factors like climatic and basin characteristics affect the water availability of a basin. Time and space distribution of rainfall, its intensity and duration, surface vegetation, soil moisture, soil characteristics, topography and drainage network are some of the important factors.

In this study, a two-dimensional numerical model for subsurface flow has been developed for the analysis of unsteady flow for subsurface drains. The governing equation is the two-dimensional Richard’s equation in the mixed form. A strongly implicit finite-difference scheme has been used to solve the governing equation.

The model has been validated using the available analytical results of the one side drains. Validation of the model indicates good agreement between the results. It has been used to simulate a hypothetical case of subsurface drains with parallel drains. The present numerical model can be used to simulate the unsteady subsurface drainage problem having a side drain and parallel drains at both sides.

The study attempts to apply Geomorphological Instantaneous Unit Hydrograph (GIUH) and Geographical Information Systems (GIS) based approach for flood estimation. The design storm data of four catchments along with morphological characteristics have been considered. The geomorphological parameters and time area diagrams for each of the dam catchments were generated using the GIS package, Integrated Land and Water Information Systems (ILWIS).

The geomorphological parameters together with the time-area diagram forms an important input for the GIUH based Clark model. This model has been applied for deriving the instantaneous unit hydrograph and thereby to estimate the design flood in four dam catchments located in Luni and Chambal basins in Rajasthan viz. Jawai, Sei, Gamabhiri and Alnia. A review of the previous studies carried out using GIUH approach has been presented. Furthermore, a review of studies carried out using GIS techniques is also provided.