Recognize that land use changes can contribute, and sometimes there is a place for dams, carefully designed, located and managed to limit effects, enhance instream flows, and be lowered as needed to provide flood storage to reduce peak flows. Forest vegetation is one of the best land uses to ensure rainfall absorption and soil storage or delaying flows. Some species have high ET demands, such as pine in eastern US as confirmed in various hydrologic studies (eg, Coweeta). But serious efforts to prevent floods would be expensive, difficult, and likely sooner or later unsuccessful. Gullies are an example of a stream type that has lost its access to a floodplain, but dredging channel systems to mimic gullies causes great habitat and stability issues, greatly effecting downstream areas with high sediment loads. High sediment loading and low gradient can contribute to channel aggravation, braiding and excessive flooding as the normal bankfull channel has partially or fully filled. But even though there may be limited capacity to actually prevent floods, we can with various hydrology, meteorology and watershed management techniques, applying GIS and other skills, generally map flood prone areas, use this information to either adjust building and structural designs to handle flooding, provide warning systems, evacuation plans and routes as needed, and recognize flooding is a natural process that we might have some ability to influence, but must also learn to live with. Some of the measures to reduce such as dams or dikes may help if properly designed and maintained, managed, but when they fail, flooding effects may also be worse than expected under natural conditions. Excessive sediment loading can make flooding worse, and river dredging can contribute to instability, habitat losses and may be only temporary help. The effects of land use and climate change can contribute to factors as snow accumulation at high elevations, melt rates, alter peak flows from snowmelt dominated ecosystems. One of my biggest concerns relative to flood prediction is that designers typically pick a number, return period, such as 100 year flood estimate, but these values may have variability of + - of 40%. When dealing with urban issues, it is probably best to go to the upper portions of the confidence limit, and also consider in the possible failure of dams during extreme events. I have heard of some unique measures, such as in ancient Egypt, there was a dam built within the dam, so if the main structure failed, the backup structure would still retain much of the stored water. Civil engineers can sometimes able to design features to temporarily to up to many years control flooding, but these often are local measures that put added flooding pressure elsewhere, and since river flooding is a natural process, adjustments are seldom to be considered permanent, or to be installed without some degree of evaluation, management and/or maintenance.

There are many reasons for flooding in India. Every solution become sensitive for type of area and availability of resources around. I can say in Assam, many low lying area of Assam are directly connected to main river Brahmaputra and don't have proper banks. Places like Majuli and Kaziranga are the notable examples where we don't have natural banks or proper structures that disconnect main lands from river. Moreover Brahmaputra River Carries Huge Suspended sediment load that which gets settled in the river bed unevenly in post monsoon that which causes erosion of banks during peak flow, eventually causing breaching of Banks. So it needs proper study Terrain, Discharge and Sediment Load carried by the river in different widths regularly to report the requirements like either dredging or Bank Strengthening as well as structural manipulations to protect the river surrounding low lying lands from floods.

With Regards,

Arun, Research Scientist,

CFMS-NIH, Guwahati.

water shed management has taken to store water

low leighing area constructions are not allowed

river connection program under going

older water bodies are reclaimed to store more water

So many things are needed to be taken care off and first and foremost thing is the estimation and prediction of precipitation in real-time then follows the other Hydrological models to simulate the runoff from that precipitation which is going to happen. And after that follows the disaster preparedness plan which should be in force already including the EWS. In this disaster plan there should be different scenarios based on the magnitude of runoff and these can be developed by simulating various hydrological models in a GIS environment. Finally these action plans/EWS will vary from region to region as India comprises the highly topographic variations separate plans and models will work for different areas this will also depend on the urbanization, drainage etc. In short a lot of work is to be done and this can only be achieved when different experts collaborate including the engineers, the GIS experts, the geologists etc.