Droughts and Floods

 Ghodadoha is a rock-filled earthen dam located in one of the tributaries of the Rushikuliya river of Orissa.

The report attempts drought characterization in arid and semi-arid climatic regions of India. Drought frequency and intensity are a function of the dimensionless climatic parameter derived as a ratio of mean annual potential evapotranspiration to mean annual precipitation (Ep/Pa).

In this study, regional flood frequency relationships have been developed using L-moments for South Bihar, in the alluvial plains of Indo-Gangetic basin and Kaimur-Chhotanagpur Santhal Pargana plateau. The annual maximum peak flood data of twenty-two gauging sites whose catchment areas vary from 11.7 to 3171 sqkm have been used. The mean annual peak floods of these sites vary from 29.15 cumec to 1293.2 cumec. Comparative regional flood frequency analysis studies have been carried out using some of the commonly used frequency distributions viz Extreme Value (EV1), General Extreme Value (GEV), Normal, Log Pareto (GPA) and Wakeby based on L-moments approach.

Floods are common in most parts of India particularly during the monsoon season. Flood control and mitigation involves flood plain mapping, zoning, insuring and warning systems as floods cannot be avoided. These measures minimize damage and loss in terms of life and property. In this regard real-time data based decision supports systems (DSS) are crucial for effective flood management.

The report, a part of the regular work programme of the Flood Studies Division of the National Institute of Hydrology presents a literature review on modeling debris flow. Occurrence of debris flows is a common natural phenomenon and denotes the rapid flow of debris with sufficient water to disperse grains uniformly throughout the entire depth. Dam break flows, landslides and flows in a mountainous terrain are some of the examples.

In this study, an attempt has been made to develop a regional flood formula using L-moments for the north Brahmaputra river system. The annual maximum peak flood data of twelve gauging sites of the north bank tributaries of the river have been considered. The screening of the data has been carried out for assessing the suitability of the data for regional flood frequency analysis by computing the Discordancy Measure (Di) in terms of L-moments. Also, homogeneity of the region has been tested using the L-moment based heterogeneity measure, H.

The study evaluates the applicability of Artificial Neural Networks (ANN) in rainfall-runoff process modeling for the Ajay river basin, Jharkhand to predict the 6-hour ahead runoff at Sarath. Initially three flood events were considered for training, to find out the weights between different layers of the network. The back propagation algorithm has been used for optimization of weights. The developed ANN was validated for rest of the flood events.

In the present study, two different Artificial Neural Networks (ANN) were developed for Dharoi reservoir, Gujarat, one for flood control operation and another for conservation operation. In recent years, ANNs are increasingly being used to predict water resources variables particularly in the operation of reservoirs, the most important elements of complex water resources systems, constructed for spatial and temporal distribution of water.

The report presents the effect of non hydrostatic pressure distribution on dam break flood wave movement. Dam break flood moves with non-hydrostatic pressure distribution in the vertical direction. However, almost all the mathematical models for dam break flows use Saint-Venant equation, which presume hydrostatic pressure in the vertical direction. In this report, an attempt has been made to use Boussinesq equations in the mathematical model. 

Article Courtesy : Reuters AlertNet
Written by: Nita Bhalla

NEW DELHI (AlertNet) - Floods triggered by heavy monsoon rains have killed more than 50 people and displaced almost half a million more in India's south and northeast, say government officials.

Overflowing rivers and reservoirs have inundated low-lying villages mainly in India's oil and tea-rich state of Assam, but also on the opposite side of country in the southwestern coastal state of Kerala.

Flood-affected people sit in a damaged hut
as they wait for relief supplies in Lakhimpur
district, in India's northeastern state of Assam.
FILE PHOTO, July 2009. REUTERS/Stringer

According to the ministry of home affairs, almost one million people have been hit by the floods, forcing almost half a million to leave their water-logged villages and seek shelter in government relief camps.

Mountainous Assam, where five people have drowned, has been the worst-affected with 13 out of 27 districts hit by flooding, including Kokrajhar, Lakhimpur, Baksa and Bongaigaon.