METER AND NON-METER FALLS The falls may be divided into following two types: 1. Meter falls 2. Non-meter falls. 1. Meter Falls. The falls which can be used to measure the discharge flowing over them, are known as meter falls. Such falls must have broad crest so that the discharge coefficient remains constant under variable head. Glacis type falls are most suitable as meter falls. If section of the channel at the site of the fall has to be flumed. From economic considerations, smooth U/S transition. Should be provided to avoid turbulences and also to maintain accurate stage-discharge relationship. 2. Non-meter Falls. The falls which cannot be use to measure the discharge passing through them, are known as non-meter falls. Vertical drop falls cannot be used as meter falls. Some vacuum is developed under the nappe of falling water, which causes non-uniform flow conditions.

TYPES OF SPILLWAYS The spillways may be broadly classified as: Emergency spillways, and Main spillways. EMERGENCY SPILLWAYS Main spillway is the spillway which is called upon to work under normal conditions of flood. Emergency spillway is provid to deal with abnormal conditions of flood. Under normal flood conditions, the emergency spillways are not required to work. They may be called upon to work under following abnormal conditions. Rise is water level in the reservoir is continuing above the maximum permitt level even when main spillway and other outlet works are working at their full capacity. This happens when flood greater than design flood has occurred. When, due to certain reasons, enforced shut down of the outlet works have to be applied and flood water is entering the reservoir with full vigour. If spillway gates have got struck down and cannot be opened immediately. In all the above three conditions the…

MODES OF FAILURE OF GRAVITY DAMS A gravity dam can fail due to the following reasons: Overturning of the dam Sliding of the dam Crushing of the dam or Foundation Development of tension in the dam. 1. Overturning of the Dam. If the resultant of all the possible forces (internal as well as external) acting on the dam cuts the base of the dam downstream of the Toe, the darn would overturn unless it can resist tensile stresses. To safeguard the dam against overturning, the resultant of the forces should never be allowed to go down stream of the Toe. If resultant is maintained within the body of the dam, there will be no overturning. All the forces acting on the dam cause moments. Some of the forces help maintain stability of the dam, while others try to disturb the stability. The moments of the forces, helping dam to maintain…

FORCES ACTING ON A GRAVITY DAM A detailed sketch of a gravity dam is shown in Fig. 13.1. All the predominant forces, that act on the dam, have been shown in the figure itself. The forces that act on the dam are the following: Weight of the dam Horizontal hydrostatic pressure due to water Uplift pressure due to water percolated under the dam Earthquake pressure Wind pressure Ice pressure Wave pressure Pressure due to silt deposited on U/S face. Out of above eight forces, acting on the dam, first three forces are the major forces that are considered in the design. All other forces are not of much significance and are considered only under specific conditions. 1. Weight of the Dam. It is the most important force, particularly for gravity dams. Stability of the dam largely depends upon this force. For the design purpose only unit length of the dam…

METHODS OF MEASURING THE DISCHARGE Discharges of rivers, streams and canals can be measured by following methods: Area velocity method, Weir method, Metric flumes method, Chemicals method, Stage discharge curve method, From power plant records. 1. Area Velocity Method. This is the direct method of computing the discharge in a stream by measuring its velocity and area of flow. The methods of computing average velocity of flow and also those of area of cross-section of flow, have been discussed earlier in this chapter. The discharge is nothing but a multiplication of the average velocity of flow and that of area of cross-section of water. 2. Weir Method. Various kinds of weirs are installed across the river streams to measure the discharge. The head of water over the weir crest is measured and the discharge is calculated by using the appropriate formula. Weirs are generally used for measuring the discharge of…

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…