2. Crop Water Requirement and Reservoir Planning , Water Resources Engineering, CE 4005 Same as CV 4005

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For 4th Semester Polytechnic CE Students
Written by Garima Kanwar | Blog: Rajasthan Polytechnic

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Subject: Water Resources Engineering, CE 4005 Same as CV 4005

Branch: Civil Engineering 🏗️
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2. Crop Water Requirement and Reservoir Planning 🌾💧

The planning of water usage for crops and reservoir systems is essential for optimizing agricultural output and managing water resources efficiently. This section covers the key concepts related to crop water requirements, irrigation methods, and the planning of reservoirs.

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2.1 Irrigation and its Classification 💦🌱

Irrigation is the artificial application of water to soil to assist in the growth of crops. It is an essential practice in agriculture, especially in regions that lack sufficient rainfall.

Classification of Irrigation:

1. Surface Irrigation: Water is applied directly to the soil surface (e.g., flood, furrow, and basin irrigation).
2. Drip Irrigation: Water is delivered directly to the roots of plants through a network of pipes or tubes.
3. Sprinkler Irrigation: Water is sprayed over the crops similar to natural rainfall using pipes and sprinklers.
4. Subsurface Irrigation: Water is applied beneath the soil surface using pipes or tubing.

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2.2 Crop Water Requirement 🌾💧

Crop Water Requirement is the amount of water needed to meet the water demand of a crop at various stages of growth. It is essential for maximizing crop yield and efficient water management.

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2.2.1 Cropping Seasons 🌱🌦️

Cropping Seasons are periods during which different crops are grown based on temperature, rainfall, and other climatic conditions.

• Kharif (Monsoon) season: Grows in the rainy season (June to September).
• Rabi (Winter) season: Grows in the winter season (October to March).
• Zaid (Summer) season: Grows during the summer (March to June).

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2.2.2 Crop Period 🌾🗓️

Crop Period refers to the time duration for which a crop requires irrigation from planting to harvesting. It is typically measured in days and varies by crop type.

• Example: The paddy crop may require 120–150 days to grow, whereas wheat may require about 100–120 days.

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2.2.3 Base Period ⏳

Base Period is the time taken for water to be used in the irrigation system to grow a crop. It is the time between the first irrigation and the final harvest of the crop. The base period helps in planning the amount of water required for different crops during their growth.

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2.2.4 Duty 🌾

Duty refers to the area of land that can be irrigated by a unit of water over a specified period. It is a measure of water efficiency.

• Example: If 1 cubic meter of water irrigates 2 hectares, the duty is 2 hectares per cubic meter.

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2.2.5 Delta 🌊

Delta is the total depth of water required by a crop during its growing season. It is usually expressed in millimeters or centimeters and represents the total water needs for the entire crop period.

• Example: A crop might need a delta of 400 mm over its growing season, meaning it requires 400 mm of water throughout the crop period.

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2.2.6 CCA (Culturable Command Area) 🌾🏞️

CCA refers to the total area of land that can be effectively irrigated under a particular irrigation system. It is the area where crops can be grown effectively using available water resources.

• Example: If an irrigation system can supply water to a total area of 100 hectares, then the CCA is 100 hectares.

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2.2.7 GCA (Gross Command Area) 🌍💧

GCA refers to the entire area of land that is served by an irrigation system, including non-culturable land and areas where irrigation may not be fully effective.

• Example: A canal system might serve 120 hectares of land, but only 100 hectares are actually cultivable. Thus, the GCA is 120 hectares, while the CCA is 100 hectares.

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2.2.8 Intensity of Irrigation 🌧️💧

Intensity of Irrigation refers to the extent of irrigation used during the crop season. It is expressed as a percentage, which indicates how much water is applied relative to the crop's total water needs.

• Formula:

  $$\text{Intensity of Irrigation} = \frac{\text{Area irrigated}}{\text{Total Area}} \times 100$$
  

• Example: If 80 hectares of a 100-hectare field are irrigated, the intensity of irrigation is 80%.

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2.2.9 Factors Affecting Duty 🌿💧

The Duty of water can be affected by several factors:

1. Soil Type: Sandy soils allow faster water drainage, requiring more frequent irrigation.
2. Crop Type: Different crops have varying water requirements.
3. Climate: Higher temperatures and evaporation rates increase the duty.
4. Water Quality: High salinity in water may reduce the effectiveness of irrigation.
5. Irrigation System: The efficiency of the irrigation system also influences the duty.

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2.2.10 Problems on Water Requirement and Capacity of Canal 💧🔧

Some common problems in managing water requirements and canal capacity include:

1. Waterlogging: When there is too much water in the soil, it can damage crops and reduce soil fertility.
2. Canal Siltation: Over time, silt accumulates in canals, reducing their capacity to transport water efficiently.
3. Inadequate Water Supply: The demand for water may exceed the supply, causing irrigation problems.

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2.3 Methods of Application of Irrigation Water and its Assessment 💧🌾

There are various methods to apply water to crops:

1. Flood Irrigation: Water is applied by flooding the field. It's common for rice cultivation.
2. Furrow Irrigation: Water is applied to furrows or narrow trenches along the rows of crops.
3. Drip Irrigation: Water is slowly released directly to the roots of the plants, minimizing wastage.
4. Sprinkler Irrigation: Water is sprayed over the crops like natural rainfall.

Assessment: Proper assessment of irrigation methods ensures efficient water use and reduces wastage.

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2.4 Surveys for Irrigation Project, Data Collection for Irrigation Project 🗺️📊

Surveys and data collection are essential for the successful planning and implementation of irrigation projects.

• Topographic Survey: Mapping the terrain and identifying the slope, water sources, and suitable land.
• Hydrological Data: Collection of data on rainfall, streamflow, groundwater levels, etc.
• Soil Survey: Analyzing soil texture, permeability, and fertility for irrigation suitability.

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2.5 Silting of Reservoir 🏞️💧

Silting refers to the accumulation of soil particles, mainly from eroded land, in a reservoir, reducing its storage capacity.

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2.5.1 Rate of Silting ⏳

The Rate of Silting is the amount of soil deposited in the reservoir over a period. This rate depends on the topography, land use, and rainfall intensity.

• Formula:

  $$\text{Rate of Silting} = \frac{\text{Volume of silt deposited}}{\text{Time period}}$$

• Example: If a reservoir receives 1000 cubic meters of silt in one year, its silting rate is 1000 cubic meters per year.

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2.5.2 Factors Affecting Silting and Control Measures 🛑🛠️

Factors Affecting Silting:

1. Soil Erosion: High erosion rates in the catchment area lead to more silt being washed into the reservoir.
2. Rainfall Intensity: Heavy rains cause more erosion, increasing silting.
3. Vegetation: Lack of vegetation leads to soil being easily eroded.

Control Measures:

1. Afforestation: Planting trees in catchment areas to reduce soil erosion.
2. Terracing: Creating terraces on sloped land to reduce runoff.
3. Sediment Traps: Building barriers or sediment traps in reservoirs to capture silt before it settles.

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Diagram: Irrigation System with Canal and Reservoir 🌾💧

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Summary 🌾💧

The efficient management of crop water requirements and reservoir planning ensures the proper use of water resources. Understanding concepts like cropping seasons, crop periods, duty, delta, and factors affecting irrigation helps optimize water use in agriculture. Additionally, managing issues like silting in reservoirs and applying the appropriate irrigation methods are crucial for sustainable agriculture.

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