Water resource engineeringChapter 9

Department of Civil Engineering

Introduction

Hydrology is the science which deals with the occurrence, distribution and movement of water on the earth, including that in the atmosphere and below the surface of the earth.

Hydrological cycle

Sources of water

At global scale, 71% water in earth’s surface.Total volume of water in hydrosphere is

estimated is 1.4 billion km3.97% of water is ocean water in total volume of

hydrosphere, and rest 3% of water is of fresh water.

Types of water sources

Types of water sources

Surface water sources

Sub- surface water sources

Surface water resources

Sea water

Ponds and Lakes

Natural large sized depression on the surface of the earth.Surface runoff from the catchment area, From the Underground water.

Streams and Rivers

Streams and rivers can be generated from the rainfall that does not evaporated runoff to the sea.

Impounding Reservoirs

Subsurface water resources

Water use and its conservation

1.) Water requirements for Municipal supplies

Water requirements for irrigation

Water requirements for hydropower

Water requirements for navigation, Recreation Navigation provides us cheap means of transport without

any consumption of water. The basic requirement for recreation is that the reservoir

should remain nearly full during the recreation season to permit boating, fishing, swimming and other water sports.

Conservation of water Rainwater is a natural gift so conservation of water is very

essential. Over the years, rising populations, growing industrialization

& expanding agriculture have increased up the demand of water.

Water conservation can be done by constructing dams, reservoirs, artificial lakes, ponds, by digging wells because water conservation has become the need of the day.

To fight against the global warming, then it is very essential to conserve the water. Minimum waste and loss of water should be done.

Improved water management practices that reduce the wastage of water. water efficiency is a tool of water conservation. That results in more efficient water use and thus reduces water demand.

Objective of water conservation efforts Sustainability:- To ensure availability for future generations, uses of water

should not exceed its natural replacement rate. Energy conservation:-Water pumping, delivery and waste water treatment facilities

consume a significant amount of energy. Habitat conservation:-Minimizing human water use helps to conserve water.

Water Conservation Measures The objective of water conservation can be achieved through

massive efforts on the conservation and utilization of water on sustainable basis.

1.) Domestic conservation:- Repair all leakages. Do not waste water. Use minimum water as required. Use water meter to know the consumption of water throughout a

day.2.) Agricultural conservation:- Use drip irrigation or sprinkler irrigation. Do not encourage wasteful irrigation system. To construct the small reservoirs and construct a roof over it to

reduce evaporation rate. Use lined canals to reduce seepage and evaporation. By efficient use of ground water and surface water.

3.) Industrial conservation:- Use such cooling system which uses less water. Reuse the cooling water for irrigation or other purpose. Develop new techniques and equipments which uses less water. Install water treatment plant and waste water treatment plant to

conserve the water and make them for reusing it for irrigation purpose.

4.) Rain water harvesting:- In semi-arid and arid regions, both the surface water and the

ground water are having less water therefore the collecting and preserving water requirement is at the peak point. This collection of rainwater is called water harvesting, which is defined as collection of rainwater and runoff primarily for irrigation, human and livestock consumption.

Rainwater Harvesting Techniques1.) Rainwater collection-Roof top rainwater harvesting.2.) Runoff collection- Surface runoff harvesting.3.) Recharge to ground water4.) Runoff enhancement

Rainwater collection: Roof Top Rainwater Harvesting Rooftop rain water harvesting is the technique through

which rain water is captured from the roof catchments and stored in sub-surface ground water reservoir.

The main objective of rooftop rainwater harvesting is to make water available for future use.

Capturing and storing rain water for use is particularly important in dry land, hilly, urban and coastal areas.

The quality of harvested rainwater is usually clean following proper installation and maintenance.

Need for Roof top rain water harvesting:- To solve the purpose for increasing water. To avoid flooding of roads. To avoid ground water pollution. To improve the quality of ground water. To reduce the cost of pumping of ground water. To reduce soil erosion. To avoid the decrease level of ground water table.

Components of the rooftop rainwater harvesting techniques

1.) A Collection area:-•The surface that receives rainfall directly is the catchment of rainwater harvesting system. •Roofs are ideal as catchment area as they easily collect large volume of rainwater.2.) A conveyance system:-•A conveyance system is required to transfer the rainwater from the roof catchment area to the storage system by connecting roof pipes.3.) Storage tanks:-•Depending upon the space available, storage tanks can be placed above the ground or under ground.4.) Delivery system:-•Delivery system which delivers rainwater and it usually includes a small pump, a pressure tank, and a tap, if delivery by means of simple gravity on site is not feasible.

Rainwater Harvesting Techniques1.) Rainwater collection-Roof top rainwater

harvesting.2.) Runoff collection- Surface runoff harvesting.3.) Recharge to ground water4.) Runoff enhancement

Runoff Collection

Small dams

Check dams are constructed in natural channels to impound the runoff water up to certain depth in the channel.

The excess water is allowed to flow over the dam.

The impounded water slowly infiltrates into the soil and recharges the ground water aquifer.

Check dams are controlling the erosion of soil. In addition to, it also serves to slow the movement of water, allowing increased percolation into the soil.

Run off collection

Ponds and Reservoirs

Ponds and reservoirs are constructed to store runoff or spring water for irrigation, domestic purpose.

Such reservoirs are also used for production of fish, aquatic fruits and vegetables.

The storage capacity of ponds can be increased by desilting and widening.

It improves the quality and quantity of ground water recharge.

There are two types of ponds are generally constructed;

The impounding type:- A retaining wall is constructed to block the flow of water into a natural storm drain.

The dog cut type:- where a pond is constructed by excavating area for storing the runoff or the spring water in it.

Rainwater Harvesting Techniques1.) Rainwater collection-Roof top rainwater

harvesting.2.) Runoff collection- Surface runoff harvesting.3.) Recharge to ground water4.) Runoff enhancement

Recharge to ground water Recharge to ground water is a new concept of rain water

harvesting and the structures generally used are: Pits Trenches Dug wells Hand pumps Recharge walls Underground reservoirs Lateral shafts with bore halls

Rainwater Harvesting Techniques1.) Rainwater collection-Roof top rainwater

harvesting.2.) Runoff collection- Surface runoff harvesting.3.) Recharge to ground water4.) Runoff enhancement

Runoff Enhancement Recent studies have shown that under favorable conditions

on an average about 10% increase in precipitation can be expected by this technique.

Introduction to Dams, Weirs, Barrages and Check Dams

Dams A dam is a hydraulic structures constructed across a river

or a natural stream to store water on its up stream side. It is an impervious barrier put across a river or a natural

stream to create a reservoir for impounding water, or to facilitate diversion of water from the river.

Storage of water is utilized for following objectives: Hydropower Irrigation Water for domestic consumption Drought and flood control For navigational facilities Other additional utilization is to develop fisheries

Structure of Dam

Heel

Gallery

Toe

Spillway(inside dam)

Crest

NWLNormalwater level

MWLMax. level

Free boardSluice way

Upstream Down stream

Heel: contact with the ground on the upstream side

Toe: contact on the downstream side.

Abutment: Sides of the valley on which the structure of the dam rest.

Galleries: small rooms like structure left within the dam for checking operations.

Diversion tunnel: Tunnels are constructed for diverting water before the construction of dam. This helps in keeping the river bed dry.

Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side.

Sluice way: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side.

Gravity Dam•These dams are heavy and massive wall-like structures of concrete in which the whole weight acts vertically downwards.

Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world.

Bhakra Dam is across river Sutlej in Himachal Pradesh

The construction of this project was started in the year 1948 and was completed in 1963 .

• It is 740 ft. high above the deepest foundation as straight concrete dam being more than three times the height of Qutab Minar.

• Length at top 518.16 m (1700 feet); Width at base 190.5 m (625 feet), and at the top is 9.14 m (30 feet)

• Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world.

Buttress Dam: Buttress Dam – Is a

gravity dam reinforced by structural supports

Buttress - a support that transmits a force from a roof or wall to another supporting structure.

This type of structure can be considered even if the foundation rocks are little weaker.

These type of dams are concrete or masonry dams which are curved or convex upstream in plan

This shape helps to transmit the major part of the water load to the abutments

Arch dams are built across narrow, deep river gorges, but now in recent years they have been considered even for little wider valleys.

Arch Dams:

Earth Dams They are trapezoidal in

shape Earth dams are

constructed where the foundation or the underlying material or rocks are weak to support the masonry dam or where the suitable competent rocks are at greater depth.

Earthen dams are relatively smaller in height and broad at the base

They are mainly built with clay, sand and gravel, hence they are also known as Earth fill dam or Rock fill dam

Weirs & Barrages A weir is an impervious barrier constructed across a river to raise the water level on the

upstream side. The water is raised up to the required height and the water then flows over the weir. Weirs have traditionally been used to create mill ponds. They are also used to prevent

flooding, measure discharge, and help render a river navigable. A Barrage is a type of low head, diversion dam which consists of a number of large gates

that can be opened or closed to control the amount of water passing through the structure, and thus regulate and stabilize river water in upstream for use in irrigation and other system.

A key difference between a dam and barrages is that a dam is built for water storage in a reservoir, which raises the level of water significantly and a barrage is built for diverting water, and raises the water level only a feet; they are generally built on flat terrain across wide, often meandering rivers.