Climate and Weather

The Systems Hydrologique European – European Hydrological System (SHE) is a physically based distributed model and it provides a useful setup for understanding the importance of evaporation data and soil parameters. 

In this study, single column hydrologic simulations have been carried out for examining the sensitivity of this model to pan evaporation data of the various stations as well as the increase in conductivity of the unsaturated zone. Furthermore, the reduction in the value of exponent appearing in the Averjanov’s formula and reduction in the values of moisture content at wilting point and residual water content has been studied for a single grid of 2 km X 2 km size of the Narmada river.

The report develops rainfall-runoff modeling for simulating and forecasting the flow from a catchment, and in determining the inflow series for the ungauged catchments on the basis of records of gauged catchments.

Because of the scarcity of data, mostly lumped models have been used to model the rainfall-runoff process in a catchment. However distributed models are more accurate and need to be adopted for modeling the complex processes at the scale of basins.

The study presents automated mapping of snow cover using a new spectral channel of Indian Remote Sensing (IRS-IC) data for the Spiti sub-basin of the Satluj river basin. Snow is an important phase of the hydrological cycle and the estimation of snowmelt runoff in the Himalayan rivers, either seasonal or daily, is of immense use in proper management and use of water resources in the basins.

The study develops the wavelet element method for hydrological application purposes in general and modeling of flow in a canal due to breach of bank in particular. Due to high seasonal variability of rainfall and cyclones in coastal India, flood discharges cause frequent breaching of canals.

Canal breach modeling is of great significance in open channel hydraulics. The study of breach of a canal is a relatively new one as compared to dam breach, which is a well researched field. The analysis of the problem is complicated due to dynamics of flow within the canal. The limitations of the above model due to the one-dimensional model analysis of the problem is hoped to be overcome in two or three dimensional analysis.

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 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.

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.

The report discusses the status and progress of studies of various hydrological problems associated with mountainous areas experiencing rain and snow. The principal issues related to mountain hydrology on the local and regional scales are discussed and highlighted.

The status of the hydrological studies carried out in the mountainous basins indicates a poor understanding of basic hydrological variables like precipitation, temperature and evaporation. The non-availability of long duration hydrometeorological data for higher altitude areas is responsible for this.

The hydrological inventory of Ganga basin provides information regarding availability of hydrological data and highlights major hydrological problems of the basins. The information is a useful input in water resources planning, management and research activities.