SEMINARON

FLOOD CONTROL

Seminar guided byDr. ANIL K. MATHURProfessorSubmitted by

SANDEEP KUMARCRN. 12/571

CONTENTS

1. Introduction2. Causes of flood 3. Flood impacts4. Indian flood prone areas5. Selection of design flood6. Method of flood control7. Procedure for design of flood control project8. Conclusions

INTRODUCTION

A flood is a relatively high stage of the river which is usually accompanied by overtopping of the natural banks of the river in a particular reach.

In India about 40 Mha of land is flood prone, which is 12% of the total geographical area of 328 Mha. About 12Mha of the flood prone land has been provided with some reasonable protection against floods by providing flood embankments, drainage channels, etc.

In 1976 Rashtriya Barh Ayog or National Flood Commission, was set up by Government of India to study the flood problem.

CAUSES OF FLOOD

1. High rainfall 2. Failure of hydraulic structure3. Snowmelt 4. Coastal flooding 5. Deforestation 6. Poor farming 7. Overgrazing 8. Overcultivation 9. Poor water management 10. Population pressure

FLOOD IMPACTS

1. Tangible loss: Loss can be estimated in terms of money value. Personal properties like building, materials etc. Loss of crops Loss due to disruption of business Loss due to disruption of road and railways

2. Intangible loss: Loss can't be estimated in money values. Human loss Disruption of Air / Train / Bus services Spread of Water-borne Communicable Diseases Communication Breakdown Electricity Supply Cut off Social Disruption Increase in Air / Water Pollution

INDIAN FLOOD PRONE AREAS

The rivers in India can be broadly divided into the following four regions for a study of flood problems:

1. Brahmaputra River Region2. Ganga River Region3. Northwest River Region4. Central India and Deccan Region

INDIAN FLOOD PRONE AREAS(CONT.)

OTHERSTATES43.9%

BIHAR12.71%

UTTAR PRADESH21.90%

ASSAM9.40%

WEST BENGAL7.91% ORISSA

4.18%

SELECTION OF DESIGN FLOOD

1. PROBABLE MAXIMUM FLOOD (PMF)2. STANDARD PROJECT FLOOD3. FLOOD CORRESPONDING TO A CERTAIN DESIRED

FREQUENCY

ESTIMATION OF DESIGN FLOOD1. Maximum observed flood method2. Empirical flood formula method 3. Enveloping curves method4. Unit hydrograph method5. Frequency analysis method

METHOD OF FLOOD CONTROL

1. Reservoirs2. Levees3. Flood walls4. Improvement of river channel5. Diversion of flood water to flood ways6. Watershed management for flood control7. Construction of cut-off8. Flood plain management9. Afforestation10. Flood forecasting

FLOOD CONTROL RESERVOIR

A flood control reservoir, generally called a flood-mitigation reservoir, stores a portions of the flood flows in such a way as to minimize the flood peaks at the areas to be protected downstream.

There are two basic types of flood mitigation reservoirs;(1). Detention reservoir(2). Retarding reservoir

FLOOD CONTROL RESERVOIR(CONT.)

Detention reservoir:

A reservoir having gates and valves installation at its spillway and at its sluice outlets is known as detention reservoir.

FLOOD CONTROL RESERVOIR(CONT.)

Retarding reservoirA reservoir with uncontrolled and ungated outlets is known as a retarding basin or retarding reservoirs.

LEVEES

Levee cross section must be adjusted to fit the site and available materials.Minimum top width 3 m usually recommended.River side protected by stone pitching and contrary side protected by turfing. Generally, levees run along river bank with a margin of 2 m between toe of levee and top of river bank. Sometimes, it may run some distance away from river bank.

FLOOD WALLS

Flood wall is usually of masonry or concrete.Usually constructed in which enough land is not available for levees.If land is costly or limited, it is more economical to construct flood wall.Constructed on river bank.Proper foundation should be provided and precaution should be taken against scouring.

IMPROVEMENT OF RIVER CHANNEL

Increase the discharge or velocity of stream or to decrease the stage and duration of flood.

Increase in size of cross section by widening and excavating stream bed.

Increasing velocity by smoothing river bed. Realignment of the river.

FLOOD WAYS

Low lying areas along the course of the river are known as floodways.

Depression into which a portion of the flood water diverted from a river through natural or artificial channel for temporarily storing.

After flood recedes, the store water is permitted to flow back to river.

Floodways used during periods of major floods, land can be used for agricultural purpose.

WATERSHED MANAGEMENT FOR FLOOD CONTROL

Providing vegetal cover. Conservation of water in agriculture. Creation of farm ponds. Use of cover crops

CONSTRUCTION OF CUT-OFF

During heavy rainfall when large flood discharge approaches the sharp bend of the river, it overflows its bank and submerges the surrounding area.So cut-off constructed to reduce travel time and water flow with high velocity along a straight path.

FLOOD PLAIN MANAGEMENT

An important non-structural measure. Regulates land use in flood plains to restrict damage by floods. Involves demarcation of zones in flood plains compatible with

flood risks involved.

FLOOD PLAIN ZONINGWATER SUPPLY

FACTORY

POWER HOUSE

UNIVERSITYRESIDENTIAL AREA

GOVT. OFFICEHOSPITAL

NORMAL CHANNEL

PARK

FREQUENT FLOOD

FLOOD ONCE IN 25 YEARS

FLOOD ONCE IN 100 YEARS

III IIII III II

AFFORESTATION

They hold the shores and keep the river bed in place and in shape. This helps the water flush away reducing the length of the flood.

They serve as a "filter" for floating objects (such as rocks, trees and debries), that are a major threat during floods because they crush on house and infrastructure.

They slow down the water reducing flood energy and therefore, the threat for people and buildings.

FLOOD FORECASTING AND WARNINGPRESENT SYSTEM - SCHEMATIC DIAGRAM

WEATHER FORECASTS

RIVER STAGE &DISCHARGE ATBASE STATION

RIVER STAGE &DISCHARGE AT

FORECASTING STATIONS RAINFALL

F.M. O. OF I.M.DFLOOD FORECASTINGCENTRES & CONTROL

ROOMS

FORMULATION OFFORECASTC.E., S.E.

STATE GOVT.CONTROL ROOM

PRESS RADIOP & TPOLICE FLOOD

COMMITTEE

CIVIL AUTHORITIESENGG. AUTHORITIES

DEFENCERAILWAYS

INDUSTRIES

F.M.O OF I.M.D

REGIONAL OFFICESOF I.M.D.

REGIONAL OFFICESOF I.M.D.

DOORDARSHAN

CWC HQ MINISTRY OF WR

PROCEDURE FOR DESIGN OF FLOOD CONTROL PROJECT

Estimate the project design flood and determine the flood characteristics of the area.

Identify the areas to be protected by the project. Conduct a field survey to determine the flood damages which are

likely to occur corresponding to different stages of flood. Identify suitable methods of flood control. Select suitable sites for

different works and determine the physical characteristics and topography of these sites.

Design the flood control works for different alternatives of flood control measures so that the cost estimates may be made and their effects on the flood discharge may be estimated.

Select the flood control measures or a combination of measures, which offer the desired protection at a minimum cost.

Perform the economic analysis of the benefits and costs to determine whether the selected project is economically viable.

Write the project report giving the details of the possibilities explored, the recommended measures and the expected degree of protection.

CONCLUSIONS

Flood can not be absolutely controlled, flood can only be managed to reduce flood losses.

An increase in channel conveyance provides flood control by allowing flood waves to pass more freely downstream.

Levees create a physical barrier to contain flood water and protect the flood plain from being flooded.

Reservoirs attenuate flood waves through providing flood water storage.

Flood ways provide flood wave attenuation through diversion away from the river.

Thank You!