Pleading of national policy flood control
RECOMMENDATIONS OF NATIONAL POLICY ON FLOOD CONTROL

Pleading of national policy flood control

RECOMMENDATIONS OF NATIONAL POLICY ON FLOOD CONTROL Board recommendations are as follows: In order to deal the problem of floods on a comprehensive basis very sustain and systematic efforts are need, both at administration level and general public level. These tasks are very huge is magnitude and hence measures of protection from floods should be progressively undertak. Even the best flood control measures do not provide complete protection and are aim at provid reasonable degree of protection. projects, Central Govt. should also take initiative in the matter. Flood control measures should form an integrat part of the overall development of the region in respect of water resources, economic perspective, ecological and humanitarian considerations. The flood management in a particular areas should form a part of package of measures of comprehensive plan for that area. Different alternatives with various degree of min of measures should be work out and analysed for…

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Methods of Measurement Discharge
Measurement of Discharge

Methods of Measurement Discharge

INTRODUCTION The word ‘stream flow’ is used to represent the discharge flowing in the river. It is also sometimes represented by term stream gauging. The discharge in the stream represents the run-off in the stream at a given section and includes surface run-off as well as ground water flow. Discharge has to be measured for canals also. Methods of measuring discharge for canals are more or less the same as those adopted for streams. Hence when we talk of measurement of discharge, it means measurement of discharge for both streams and canals. There may be little bit of difference in the application of the methods. Canals and streams differ in following respects.    

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Measurement of discharge streams & canals

PURPOSE OF MEASUREMENT OF DISCHARGE OF STREAMS AND CANALS The discharge of streams and canals has to be measured for following reasons. The irrigation potential of a particular river at a particular point can be estimated only if discharge characteristics of the river at that particular point of the stream are known. If flow in the stream falls too low during particular season, it may become essential to construct dam or weir. Even height of the dam or weir depends upon the discharge of the river. Storage of water is further dependent upon the available discharge which again necessitates measurement of discharge. Because water in the canal is left proportional to the area it has to irrigate, measurement of discharge again becomes necessary at all works. Regulation of canal system is almost fully based on the discharge measurement, as water in each canal has to be left equal to the…

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Flood Control
FLOOD CONTROL

Flood Control

FLOOD CONTROL Flood is a relatively high flow. The floods cause overtopping of natural as well as artificial banks of the streams. The flood is caused by run off from rainfall and/ or melting snow, too large to be confined in the banks of streams. When banks are overtopped the flood water spreads over the adjoining area and causes heavy damage to crops and property. It is not possible to prevent occurrence of floods but it is possible to prevent or reduce the damage due to floods by controlling the floods. This flood control or flood management may be defined as the prevention or reduction of the flood damage. In India about 40 million hectares of area has been identified as flood prone. Out of this about 12 million hectares have been provided with flood protections measures by March 1982. Govt. of India set up National Flood Commission in July…

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Flood Absorption & Routing
FLOOD ABSORPTION OR FLOOD ROUTING

Flood Absorption & Routing

FLOOD ABSORPTION OR FLOOD ROUTING Flood routing is a process with the help of which characteristics of hydrograph of a flood, entering the reservoir are completely change when it emerges out of the reservoir. The change in flood hydrograph characteristics takes place because certain volume of flood is store in the reservoir temporarily. The base of the modified hydrograph, which emerges from the reservoirs becomes wider and its penk gets reduced. The extent by which the inflow hydrograph gets changed due to reservoir storage can be computed by a process. It is an important technique with the help of which solution of a flood control problem is arrived at. In flood routing problem one has to calculate water levels in the reservoir, the storage quantities and outflow rates. It is used to determine the level upto which water may rise during floods and also the rate of the discharge in…

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Silt control of reservoir
SILT CONTROL OF RESERVOIRS

Silt control of reservoir

SILT CONTROL OF RESERVOIRS Entrance of silt into the reservoir may be controlled by adopting following preventive measures. Reservoir site should be properly selected. If nature of catchment soil contributing water to the reservoir is very soft, the rate of silting will he more, as soft sand will be easily carried by run-off. If slope of the catchment is steep, it will also cause more of silting, as steepness would cause increased velocity of flow of run-off and thus more erosion of the catchment soil. The tributaries carrying more of silt load to the reservoir should be provided with check bunds some where upstream of the tributaries. Check bunds would cause sedimentation of silt load upstream and comparatively clear water will reach the main reservoir. The small reservoirs created at the back of the check bunds also supply stored water to the main reservoir when supplies in the tributaries have…

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Reservoir losses
RESERVOIR LOSSES

Reservoir losses

RESERVOIR LOSSES Reservoir losses may be classified under following three heads. Evaporation losses Absorption losses Reservoir leakage or percolation losses. 1. Evaporation Losses. These are the major losses from a reservoir. This loss is affecte by expos surface area of the reservoir, wind velocity, temperature, relative humidity etc. This loss is express in cm of water depth and varies from place to place depending upon the local conditions such temperatures, relative humidity, wind etc. Average values of losses in cm for North and South India for various methods of the year are given as follows. 2. Absorption Losses. This loss of water is considerable in the beginning, but falls to very small values after some time when pores get saturat. These losses depend upon the soil forming the reservoir. These losses are not consider while planning a reservoir. 3. Reservoir Leakage or Percolation Losses. Reservoirs being very large, their banks…

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Reservoir sedimentation
RESERVOIR SEDIMENTATION

Reservoir sedimentation

RESERVOIR SEDIMENTATION All the waters entering the reservoir carry some amount of silt. The amount of silt in the water coming into the reservoir depends upon the topography, nature of the soil, vegetation cover over the catchment, and also upon the intensity of rainfall. If soil in the catchment is soft there is always possibility of sheet erosion and amount of silt in the water coming to reservoir will be more. If catchment has large slope, it will cause rain water to flow with greater velocity and possibilities of increas amount of slit in the water will occur. Similarly higher intensities of rain fall also cause greater run off and greater erosion and consequently increas amount of silt in water approaching the reservoir. If catchment has good cover of vegetation, the amount of silt in water would decrease. The silt load held in river water approaching the reservoir may be…

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life of reservoir
LIFE OF RESERVOIR

life of reservoir

LIFE OF RESERVOIR Any reservoir cannot last for ever. Ultimately all the reservoirs get silted up. Silting of the reservoir starts from the day it is created. When reservoirs are created some of its capacity is left unused. This is the capacity of the reservoir lying below the crest level of the bottom most under sluices. This storage capacity which remains unused is know dead storage. This dead storage capacity is used to accommodate deposited silt so that effective storage of the reservoir is not affected. So long as dead storage capacity of the reservoir is not silted completely, effective storage or useful storage capacity is not affected. The process of silting continues even after complete silting of dead storage. The further silting affects the effective storage of the reservoir and the reservoir does not have enough water to fully fulfil its obligations. Generally useful life of the reservoir is…

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Density Currents
DENSITY CURRENTS

Density Currents

DENSITY CURRENTS The water stored in the reservoir is generally free from silt. The flood inflow is generally muddy and heavily charged with silt. Thus during floods there are two waters having different densities present is the reservoir. Heavily silt charged water flows along the bottom of the channel towards the dam under the influence of gravity. This current of heavily silt charged water flowing along the bottom of the reservoir towards the dam is know Density current. If the density currents, are directly discharg out of the reservoir by suitably positioning and operating the sluice gates, the rate of reservoir silting can be considerably reduced.

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