An Article on Flood Control
Author: S.Hema Bindu
Optimal utilization of the water resources through appropriate conservation and management measures assumes critical importance in sustaining the life support systems. The pattern of demand for water is undergoing gradual but continuous changes towards increasing pressure for drinking and other household and commercial needs relative to the demand for irrigation as the emerging trend is towards less water demanding perennial crops in lieu of seasonal crops. Progress in this direction is quite limited and flood control works continue to be on conventional lines like strengthening the riverbanks, construction of retaining walls, embankments,
There was no attempt in the past for assessing the flood incidences, their intensity, pattern of occurrence and vulnerability of different regions. Flood proofing is feasible only after identifying the root cause of floods from its origin. It is therefore proposed to organize a basin wise study in major river systems that are vulnerable to flood, to find out the causes of flood and its intensity
It is the purpose of this paper to promote the public health, safety, and general welfare, and to minimize public and private losses due to flood conditions in specific areas by provisions designed:
A. To protect human life and health;
B. To minimize expenditure of public money for costly flood control projects;
C. To minimize the need for rescue and relief efforts associated with flooding and generally undertaken at the expense of the general public;
D. To minimize prolonged business interruptions;
E. To minimize damage to public facilities and utilities such as water and gas mains, electric, telephone and sewer lines, streets and bridges located in areas of special flood hazard;
F. To help maintain a stable tax base by providing for the second use and development of areas of special flood hazard so as to minimize future flood blight areas;
G. To insure that potential buyers are notified that property is in an area of special flood hazard;
H. To insure that those who occupy the areas of special flood hazard assume responsibility for their actions.
III CAUSES OF FLOODS:
When it rains or snows, some of the water is retained by the soil, some is absorbed by vegetation, some evaporates, and the remainder, which reaches stream channels, is called runoff. Floods occur when soil and vegetation cannot absorb all the water; water then runs off the land in quantities that cannot be carried in stream channels or retained in natural ponds and constructed reservoirs. About 30 percent of all precipitation is runoff, and melting snow masses may increase this amount. Periodic floods occur naturally on many rivers, forming an area known as the flood plain. These river floods often result from heavy rain, sometimes combined with melting snow, which causes the rivers to overflow their banks; a flood that rises and falls rapidly with little or no advance warning is called a flash flood. Flash floods usually result from intense rainfall over a relatively small area. Coastal areas are occasionally flooded by unusually high tides induced by severe winds over ocean surfaces, or by tsunamis caused by undersea earthquakes These flood losses are caused by the cumulative effect of obstructions in areas of special flood hazards, which increase flood heights and velocities, and when inadequately anchored, damage uses in other areas. Uses that are inadequately flood proofed, elevated or otherwise protected from flood damage also contribute to the flood loss
IV EFFECTS OF FLOOD:
Floods not only damage property and endanger the lives of humans and animals, but have other effects as well. Rapid runoff causes soil erosion as well as sediment deposition problems downstream. Spawning grounds for fish and other wildlife habitat are often destroyed. High-velocity currents increase flood damage; prolonged high floods delay traffic and interfere with drainage and economic use of lands. Bridge abutments, bank lines, sewer outfalls, and other structures within floodways are damaged, and navigation and hydroelectric power are often impaired. Financial losses due to floods are commonly millions of dollars each year. The flood hazard areas of the city are subject to periodic inundation which results in loss of life and property, health and safety hazards, disruption of commerce and governmental services, extraordinary public expenditures for flood protection and relief, and impairment of the tax base, all of which adversely affect the public health, safety, and general welfare.When it rains in, flood control channels, rivers, and washes quickly fill up with fast moving water, and this can create a potentially life-threatening danger to anyone who gets caught or swept away.
“A foot or two of water can cost our life! Nearly half of all flash flood fatalities are automobile related. Two feet of water will carry away most automobiles. Also avoid walking also through floodwaters, even six inches of water can sweep off our feet.”
A flash flood is a torrent of water rushing through normally dry or low-flow creeks, streams, washes, ravines, culverts, or over lower lying ground. In desert areas, a raging torrent of water may move off the mountains for miles into relatively flat terrain. The violent rushing of water collects debris and mud as it moves and becomes destructive to everything in its path.
V CONTROL OF FLOODS
The basic methods of flood control have been practiced since ancient times. These methods include reforestation and the construction of levees, dams, reservoirs, and floodways (artificial channels that divert floodwater).
1. An effective method of controlling floodwaters is to construct coordinated groups of dams and reservoirs on the headwaters of the streams that lead into the main rivers, so that water can be stored during periods of heavy runoff and released gradually during dry seasons
2. People have created a flood problem by cutting down trees and digging up the vegetable cover of the soil, thus increasing soil erosion. Flood control in these areas has been directed to restoring vegetation and instituting efficient methods of soil management, such as crop rotation and contour plowing.
3. Another method of flood control is the construction of floodways on the lower reaches of rivers to divert floodwaters. The rivers are widened at certain points and allowed to overflow. Inundation of certain confined areas prevents the flooding of other areas.
4. In the past, agricultural lands were regarded as only having the role of food production, but are now considered to have several functions, such as flood protection, fostering of water resources, and so on.
5. Flood Control Facilities With regard to integrated flood control projects, emphasis has been placed on embankment construction in coordination with the reengineering of the courses of rivers, dredging as well as the setting up of pumping stations located at the main exits of the drainage pipes behind embankments, so as to pump off rainwater that cannot be drained off by gravitational force within the city
6. Over bank Flood The primary purpose of over bank flood control of control is used primarily to protect property adjacent to the stream from frequent flooding.
7. Flood Barriers variable height flood barriers provide total flood protection to doors and windows, whilst also preserving the visual integrity of the building. Flood Barriers are the ideal flood defence for homes, commercial premises and retail outlets. Recommended uses are in House doors and windows · Driveways and garages · Business premises · Shops and Stores
8. Flood Gates Designed to provide maximum protection from impact damage and violent water, our Flood Gates allow us to leave our property with total confidence that our products, plant and possessions are safe from all but the most overwhelming flood conditions. Recommended Uses Commercial premises and industrial units likely to be unattended when flooding occurs. Isolated properties liable to be cutoff and evacuated during floods
Flood Gates can be supplied to protect up to a flood height of 1.8 metres and to an installed width of up to 6 metres.
9. Removable Dams Removable Dam system has been engineered to provide similar levels of protection to permanent flood defence schemes, but with the distinct advantage of being removable when not required – thus preserving the integrity of the landscape and architecture. The system can be used between existing structures but has been primarily designed to be completely self-supporting over almost any distance and may be specified for virtually any height of floodwater. Recommended Uses: – Roadways, subways, embankment promenades, industrial complexes, shopping precincts
11.Flood-Proofing Services All services of flood-proofed buildings – electrical, heating, road, and sewer – must also be protected from flood damage. Special valves can protect sewers and water pipes; telephone equipment and electrical transformers must be located above design flood levels. Auxiliary generators may have to be installed, and hydro lines, access roads and bridges to buildings must be protected. Buried hydro lines and gas mains must be located and designed to resist damage from possible flood erosion or uplift forces.
Basic Flood-Proofing Methods
1. Buildings on Piers, Piles, Columns or Bearing WallsElevating structures above design flood level on some kind of support provide reliable protection against flood damage. This method uses land efficiently, does not raise the flood level, and has minimal adverse effects on flood flows.
2. Making Lower Levels of Building Watertight (Closure and Seal Method) Flood-proofing the lower levels of buildings by sealing them against water penetration requires that they be made strong enough to withstand cracking from the lateral and uplift pressure of the water.
3. Surrounding Buildings with Flood-Proof Walls or Berms: This method involves generally the same considerations as those required in the design of small dams. It has several disadvantages such as increasing the possibility of catastrophic failure and is not practicable for individual buildings in dense urban areas.
4.Floodproofinr Our Home
We can take an active role in protecting our property from flood damage both prior to and during flood. Prevention Methods:
· We can divert water from our property by regarding or constructing an earthen berm. Both of these may require a permit so check with the County Planning and Development Department first.
· The construction of swales (shallow ditch) and retention areas (small shallow depressions) are other effective methods of preventing flooding. Again, We will need to check to see if a permit is required.
· If roof drainage is a problem, gutters can help direct runoff.
· Another way of protecting a building from flooding is by raising the building. This can be expensive, but may be very cost effective.
· During a Flood
· Fasten plastic sheeting or other waterproof paper across windows and doors
· if evacuation appears necessary and only if time permits:
· Turn off the electricity at the main power switch and turn off the gas at the main valve.
· Move valuable papers and personal items to upper floors or higher elevations.
· Move outdoor possessions inside, anchor them down, or tie them together so they don’t get carried away.
· Keep a battery-powered radio handy and tuned in to a local emergency broadcast station: follow all emergency instructions.
· Move to high ground or an established emergency shelter. If it is safe to evacuate by car, take nonperishable foods, blankets, a flashlight, dry clothing, and any special medications with We. Be aware that many stores and gas stations will be closed since pumps and registers may not function if electricity has been cut off.
· Do not drive where water is over the road: part of the road may be washed out or be much deeper than it looks.
· When we return to our home and find that it has been flooded, check first for structural damage. Then air out the home in case of possible gas leaks. Do not turn on gas or electricity until utility representatives have checked them for gas leaks and short circuits.
VI. METHODS OF REDUCING FLOOD LOSSES:
In order to accomplish its purposes, this includes methods and provisions for:
(1) Restricting or prohibiting uses which are dangerous to health, safety, and property due to water or erosion hazards, or which result in damaging increases in erosion or in flood heights or velocities;
(2) Requiring that uses vulnerable to floods, including facilities, which serve such uses, be protected against flood damage at the time of initial construction;
(3) Controlling the alteration of natural floodplains, stream channels, and natural protective barriers, which help accommodate or channel floodwaters;
(4) Controlling filling, grading, dredging, and other development which may increase flood damage; and
(5) Preventing or regulating the construction of flood barriers which will unnaturally divert floodwaters or may increase flood hazards in other areas
The problem of flood control has assumed national importance because of the increasing frequency and intensity of floods in all of the great river valleys as a result of deforestation. Many aspects of flood control can be handled by individual states or groups of states acting on a regional basis Encourage the mapping of the floodways to develop more effective flood control programs Maintain and re-establish forest cover ,to improve the capacity of the ground to absorb heavy rainfall. Ensure that purchasers of homes and other real property are fully informed of hazards from floods. Continue proper soil conservation measures to complement the existing systems. Improve and upgrade existing flood control measures as necessary.
About the Author
BE civil,M.E civil, Water resources study area