Open Channel Flows - Definition, Types & Comparison

Open Channel Flows - Definition, Types & Comparison of Open & Pipe Flow

Definition:

It is usually the flow in an Open Channels

Surface Flow:

The flow which is above the ground level is called surface flow.

Ground Flow:

The flow which is below the surface of the earth is called ground flow.

Hydraulics:

Deals with the study of surface water only

Ground Flow:

Deals with the surface as well as ground water water.

Partially filled pipes flow:partially filled pipes have flow wich is not enclosed on all sides and air is present above it so is under atmospheric pressure.

Differences between open and pipe flow

1. Open channel flow has a free water surface
2. Open channel flow is subjected to atmospheric pressure while pipe flow is not (when pipe is full).
3. Open channel flow is not completely enclosed by boundaries, unlike pipe flow.
4. Open channel is always under the action of gravity, while pipe can be under gravity or may flow due to some external pressure.

Open Channel flow (Free Gravity flow):

Open Chanel flow is that type of flow which is neither completely enclosed by the boundaries nor is under any external pressure but gravity. It is subjected to atmospheric pressure. e.g. Rivers, natural and artificial canals, streams, channels etc. Partially filled pipes flow is also an example of open channel flow.

Types of open channel flow

Steady Flow:

For open channel, the flow is steady if the depth of flow does not change with respect to time at a particular location or section.

Why to study open channel flow: For construction of succesful hydraulic structures. Open channel flow is difficult to deal with beacuse: Difficult to secure reliable experimental data Are od different and irregular X-sections and shapes Friction co-efficient is choiced by great uncertainity

Unsteady flow:

For open channel, the flow is unsteady if the depth of flow changes with respect to time at a particular location or section.

Uniform flow:

For open channel flow, the flow is uniform if the depth of flow remains constant along a certain length of the channel.

Non Uniform flow:

For open channel flow, the flow is non uniform if the depth of flow does not remains constant along a certain length of the channel.

Gradually Varied flow:

If the depth of flow changes over a relatively long distance along the length of a channel, then the flow is called gradually varied flow.

Rapidly Varied flow:

If the depth of flow changes over a relatively short distance along the length of a channel, then the flow is called rapidly varied flow.

Water resources & Irrigation system of Pakistan

Water Resources of Pakistan

Water Budget of Pakistan

According to the United Nations' "UN World Water Development Report", the total actual renewable water resources decreased from 2,961 m³ per capita in 2000 to 1,420 m³ per capita in 2005.

A more recent study indicates an available supply of water of little more than 1,000 m³ per person, which puts Pakistan in the category of a high stress country.

In view of growing population, urbanization and increased industrialization, the situation is likely to get worse.

In addition, increasing pollution and saltwater intrusion threaten the country's water resources.

About 36% of the groundwater is classified as highly saline.

In urban areas, most water is supplied from groundwater except for the cities of Karachi, Hyderabad and a part of Islamabad, where mainly surface water is used. In most rural areas, groundwater is used. In rural areas with saline groundwater, irrigation canals serve as the main source of domestic water.

Out of the 169,384 billion m³ of water which were withdrawn in 2000, 96% were used for agricultural purposes, leaving 2% for domestic and another 2% for industrial use. This shows the significance of agriculture in the country.

Pakistan still has the world's largest interconnected & Continous irrigation system. In 1999-2000, the total irrigated area in Pakistan was 181,000 km². Pakistan has one of the world’s largest gravity-flow irrigation systems, with:

1. Three reservoirs
2. 19 barrages
3. 12 river interlinking canals and
4. 59,200 kilometers of distribution canals.

More than 160,000 watercourses comprise the distribution network that takes water directly to the farms.

More than half of these watercourses are in Punjab—the largest of the country’s four provinces and the biggest agricultural producer. The system commands a land area of 14.3 million hectares, making it the backbone of Pakistan’s agriculture and contributes one-fourth of country’s total gross domestic product (GDP).

About 29% of water is generated through hydropower.

Major Barrages of Pakistan

Key facts Barrage Year of Completion Max. Design Discharge (cusecs) No. of Bays Max. Flood level from floor(ft) Total Design Withdrawals for Canal (cusecs) Chashma 1971 1,100,000 52 37 26,700 Guddu 1962 1,200,000 64 26 - Jinnah 1946 950,000 42 28 7,500 Kotri 1955 875,000 44     43.1 - Sukkur 1932 1,500,000 54 30 47,530 Taunsa 1959 750,000 53 26 36,501

Purpose, Necessity & Importance of Irrigation Engineering

Importance of Irrigation Engineering

• In the next 35-45- years, world food production will need to double to meet the demands of increased population.
• 90% of this increased food production will have to come from existing lands. 
• 70% of this increased food production will have to come from irrigated land

Purposes of Irrigation

• Providing insurance against short duration droughts
• Reducing the hazard of frost (increase the temperature of the plant)
• Reducing the temperature during hot spells
• Washing or diluting salts in the soil Softening tillage pans and clods
• Delaying bud formation by evaporative cooling
• Promoting the function of some micro organisms
  
  

Objectives of irrigation

• • To Supply Water Partially or Totally for Crop Need
  • To Cool both the Soil and the Plant
  • To Leach Excess Salts
  • To improve Groundwater storage
  • To Facilitate continuous cropping
  • To Enhance Fertilizer Application- Fertigation

History & Introduction to Irrigation Engineering

History of irrigation Engineering

1. Ancient civilizations rose over irrigated areas
2. Egypt claims having the world's oldest dam, 108m long, 12m high, built 5,000 years ago
3. 6,000 years ago, Mesopotamia supported as many as 25 million people.
4. The same land today with similar population depends on imported wheat for food
   
   

Introduction to Irrigation Engineering

1. Irrigation is the controlled application of water to croplands. Its primary objective is to create an optimal soil moisture regime for maximizing crop production and quality while at the same time minimizing the environmental degradation inherent in irrigation of agricultural lands. Irrigation is thus critical for food security in semi-arid and arid areas
   Irrigation has two primary objectives:
   
   1. To supply the essential moisture for plant growth; &
   2. To leach or dilute salts from the soil.
      
   Irrigation water management deals with the frequency of irrigation, depth of water to be applied, and measures to increase the uniformity of applications.
   Irrigation management should be a set of practices designed to maximize efficiencies and minimize the labor and capital requirements of a particular irrigation system.
   
   

Role of civil engineers in Irrigation Engineering

1. Irrigation is a cross cutting sector that involves civil engineers, hydrologists, environmental experts, land surveyors, agricultural scientists and others, civil and irrigation engineers were important for successful irrigation schemes
   
   • The supply of water at farm turnout
   • Water storage in Dams
   • Water conveyance
   • Flood control
   • Supplying water WHEN needed and by the QUANTITY needed – irrigation scheduling e.g in Weirs, Barrages
     
   • Hydraulic Structures - Headworks, Cross Drainage works
   
   
   
   

Definition

Definition

Irrigation is the controlled application of water to croplands.  Its primary objective is to create an optimal soil moisture regime for maximizing crop production and quality while at the same time minimizing the environmental degradation inherent in irrigation of agricultural lands.

OR

Irrigation is the application of water to the soil to supplement natural precipitation and provide an environment that is optimum for crop production. Well Irrigated crops produce more food.