Nepal Engineering Council License Exam Prep - Irrigation & Drainage PDF

NEPAL ENGINEERING COUNCIL LICENSE EXAMINATION PREPARATION COURSE FOR CIVIL ENGINEERS on Irrigation and Drainage Er. Kaishar Ansari 1 7. Irrigation And Drai...

NEPAL ENGINEERING COUNCIL LICENSE EXAMINATION PREPARATION COURSE FOR CIVIL ENGINEERS on Irrigation and Drainage Er. Kaishar Ansari 1 7. Irrigation And Drainage 7.1 Water demand estimation 7.2 Design of canals 7.3 Diversion headworks 7.4 River training works 7.5 Regulating and cross-drainage structures 7.6 Water logging and drainage 2 7.1 Water demand estimation Crop water and irrigation water requirements; Water availability for irrigation; Command areas; irrigation intensity; Duty, Delta and their relationship; Water losses and irrigation efficiencies; effective rainfall; Soil-moisture-irrigation relationship; Depth and frequency of irrigation; Design discharge for canals 3  Introduction of irrigation Irrigation can be defined as the science of artificial application of water to crops throughout the growth period to attain full maturity or for maximum crop production The pH value of irrigating water is 6 to 8.5 The soil becomes practically infertile if its PH is more than 11 Advantages Irrigation does not reduce the crop growing period 1. Increasing in food production Necessity of irrigation 2. General prosperity -Inadequate rainfall -Uneven distribution of rainfall with respect to time and 3. Elimination of mixed cropping area 4. Navigation -Increasing the crop yield 5. Flood control -Growing number of crop -Growing perennial crop 6. Generation of hydropower Disadvantages 7. Domestic and Industrial water supply 1. Water pollution [seepage of fertilizer(nitrate) into the groundwater 8. Afforestation reservoir] 2. Formation of marshy land 9. Protection from famine 3. Water logging due to over irrigation 4. Colder and damper climate. 5. Loss of valuable lands Arid region/zone Status of irrigation in Nepal Without irrigation no crops can be grown Total area=1,47,181 km2 Rainfall less than 25 cm per year Total agricultural land = 41,210 km2 (28%) Semi Arid Region/Zone Without irrigation some low inferior crops can be Total Cultivable area = 26,42,000 ha grown Total irrigable area = 17,66,000 ha Rainfall 25 cm to 50 cm per year At the end of the fiscal year 2076/2077, History of irrigation in Nepal surface irrigation = 10,02,746 ha In 1979 B.S (1922 A.D) construction of first irrigation Sub surface irrigation=4,79,882 ha canal of Nepal i.e Chandra canal started and was completed in 1985 B.S (1928 A.D) Total irrigated area=14,82,298 ha Chandra canal was constructed in Triyuga river of Farmer water course=2,80,041 ha Saptari district and having a command area of 10500 ha First irrigation development policy was developed in 2049 B.S and currently irrigation development policy 2070 B.S is in use. Department of irrigation was developed in 2044 B.S Water Quality Sodium absorption ratio (SAR) = SAR Value Type of water Suitability 0-10 Low sodium water Suitable for all types of crops and soil 10-18 Medium sodium water Suitable for coarse soil with good permeability 18-26 High sodium water Harmful for all soils and requires good drainage > 26 Very high sodium water Not suitable for irrigation  Classificaton/Types of irrigation Surface Irrigation Sub-surface Irrigation Water is applied directly on ground Water is applied directly in surface the rootzone of plant Lift Irrigation Flow Irrigation Water is applied by pumping from Water flows freely under lower elevation to higher action of gravity elevation. e.g. flow in canal e.g. well, tubewell etc Natural Sub-surface Irrigation Artificial sub-surface Irrigatio Water is applied in the Water is applied in the Perennial Irrigation Flood/Innundation Irrigation rootzone of plant due to rootzone of plant by using Controlled Irrigation Uncontrolled Irrigation seepage through canals or perforated pipe network. Water is applied to the Agricultural land is kept water bodies. E.g drip irrigation field throughout the submerged like flood year 5/8/2024 condition Kaishar Ansari 7 Wild/Free flooding Water is applied to the field in an uncontrolled way so called as uncontrolled flooding. Usually ditches are 20 to 50 meters apart depending upon the slope, soil texture and types of crops sown. Suitable on flat rolling land. This method has lowest water application efficiency Border strip flooding method Land is divided into a number of strips with the help of low levees Each strip is generally of 10 to 20 m in width and 100 to 400 m in length Suitable for some close crops like rice, pastures etc Check area flooding method Most common and widely practiced method in Nepal. Area is divided into small plots by low levees called as check areas. Check area varies from 0.2 ha to 0.8 ha. Suitable method for cereal crops Suitable for more permeable as compared to border and free flooding method Basin Flooding Method Most suitable method for orchard farming or gardening Basins are made around one or more trees in shape of square, circular etc. but circular is more common so called as Ring basin method. Basins are kept submerged. This method economise water considerably. Furrow Irrigation method Suitable method for row crops like potatoes, onions, sugarcane etc. Furrows are narrow ditches excavated between rows of plants Furrow/ditches carry water and crops are planted on ridges. Depth of furrows varies from 8 cm to 30 cm and about 400 m long About 20% to 50% i.e one-fifth to one half of the land is wetted by water. Drip/Trickle Irrigation Method Water is slowly and directly applied to the root zone of plants through the nozzles present in the pipe network buried under surface Water is applied drop by drop at the rate of 2 lit/hr to 10 lit/hr. This method has highest water application efficiency of more than 90% Suitable for any type of land topography. Suitable in water scarce area. Suitable for fruits vegetables Sprinkler Irrigation Method Water is sprayed to crops in form of artificial rain. Suitable for any type of land Topography. Suitable at water scarce area with pressure Pressure of rotating head is 1.4 kg/cm2 to 2.1 kg/cm2 Having high water application efficiency of 80 to 85 % Suitable where W.T is high. Suitable for light soil having high infiltration rate. Strong wind disturbs sprinkling pattern. Suitable for fruits, vegetables, coffee, tea etc.  Duty Delta and Base period Paleo First Watering (KOR Watering) Last Watering Irrigation KOR Period Base Period Sowing Harvesting Crop Period Crop Period The time period between sowing of crop to its harvest is called crop period and is expressed in days. Base Period Time between the first watering of a crop after sowing to the last watering before harvesting is called Base period. It is expressed in days and represented by B. Generally, Crop period >Base period Practically, Crop period = Base period Delta (∆) The total depth of water, in cm, required by a crop to come to maturity is called delta (∆). Duty(D) Duty of water is defined as the hectares of land that can be irrigated by a constant supply of water at one cumecs (m3/s) throughout the base period (B). It’s unit is ha/cumecs (m3/s). As we move from canal to field duty of water increases. Duty is maximum at the field. Duty at the head of water course (outlet point) is called as outlet duty or outlet factor or outlet discharge factor. Factors affecting duty are type of soil, type of crop, temperature, wind velocity, humidity, effective rainfall etc. Relation between duty delta and base period B In S.I system ∆ = 8.64 D B In F.P.S system ∆ = 1.985 D Paleo Irrigation: Irrigation done before sowing for land preparation is called as paleo irrigation. It helps in initial growth of plant upto few cm. kor-watering: First watering after sowing when the plant has grown few cm is called as kor-wate It is usually maximum single watering followed by other watering at regular interval. kor-depth (∆ k o r ) : Depth of kor-watering is called kor-depth. kor-period(Bkor): Time period between sowing and kor-watering is called as kor-period. Bkor ∆ k o r = 8.64 Outlet factor Crop and cropping season 1. Kharif crop season: (April to September) Also called as summer crops or monsoon crops Sown at beginning of summer or end of winter and harvested at end of summer or beginning of winter. E.g Rice, maize, millet, groundnut, pulse, cotton, soybean, bajra, jwar etc 2. Rabi Crop Season : ( October to March) Also called as winter crops. Sown at beginning of winter or end of summer and harvested at end of winter or beginning of summer. E.g Wheat, barley, lineseed, potatoes, mustard gram etc. 3. Perennial Crops: Crops having base period of more than 300 days. E.g sugarcane, flowers, fruits etc.  Leguminous Crops: Belongs to legume family i.e peas, beans, lentils etc. These crops roots have nodules that contains nitrogen fixing bacteria called as Rhizobium bacteria that helps to improve the nitrogen content of the soil. E.g peas, beans, hemp, gram, groundnut etc.  Cash Crops: Also called as profit crops. These crops are grown to sell for profit. E.g Coffee, tea, vegetables, fruits etc.  Crop Ratio: Also called as Rabi-Kharif ratio. Defined as ratio of area irrigated during rabi season to area irrigated during kharif season Generally taken as 2:1  Base KOR KOR Root zone Delta Duty Crop period depth period depth (cm) (Days) (cm) (weeks) (ha/cumecs) (cm) Rice 120 120 19 2-4 775 90 Wheat 40 120 13.5 3-8 1800 100 Sugarcane 120 330 16.5 - 800 150 Cotton 50 - - - - 140 Maize 25 - - - - 100 Tobacco 75 - - - - 80 Barley 30 - - - - 110 Fodder Crops (To feed Domestic Animals e.g. Hay, 2000 maize, barley, legumes etc.)  Gross Command Area (GCA): Total area that can be irrigated when design discharge is always available Culturable command area (CCA): Unculturable command area Part of GCA in which cultivation is Part of GCA in which cultivation is not possible possible 70% to 80% of GCA E.g building, bridge, barren land, River etc. Culturable cultivated area Culturable uncultivated area That part of CCA which is That part of CCA which is not cultivated during present cultivated during present season. season  Commanded Area and Irrigation Intensity Commanded area is defined as the area that can be irrigated by canal. Gross Commanded Area (GCA) It is the total area (cultivable as well as uncultivable like ponds, roads, residential area, etc.), within the irrigation boundary of irrigation project, which can be economically irrigated considering that unlimited quantity of water is available. Culturable/Cultivable Commanded Area (CCA) Part of (GCA) in which cultivation is possible. CCA is generally taken as 70% to 80% of GCA. Unculturable command area: That part of GCA in which cultivation is not possible. E.g Road, forest, barren land, building etc. Culturable cultivated area That part of CCA which is proposed to be irrigated in present season. Culturable uncultivated area That part of CCA which is not irrigated during present season. Intensity of Irrigation (IOI) Percentage of the CCA purposed to be irrigated. Seasonal Intensity of Irrigation for a season and Annual Intensity of Irrigation for a year. Annual intensity of irrigation is summation of seasonal intensity of irrigation within a year Annual IOI = (IOI)R + (IOI)K For example, If CCA of an irrigation field is 100 hectares, of which 40 hectares is cultivated in kharif season and 70 hectares in Rabi season. The Intensity of irrigation for Kharif is 40/100 × 100% = 40% and for Rabi will be 70/100 × 100% = 70%. The annual intensity = 40% + 70% = 110%. Annual IOI can be more than 100% Overlap Allowance: The extra discharge required to mature the crop which extends from one season to another season is called as overlap allowance. Capacity Factor: Defined as the ratio of mean supply discharge in a canal to its design discharge. Time Factor: Defined as the ratio of actual operating period of canal to the crop period/Base period. This factor helps to check the danger of over-irrigation. Full Supply Coefficient: Defined as the ratio of area irrigated during base period to design discharge at the head of canal. Also called as Duty on Capacity. (Q). The culturable command area for a distributary channel is 10000 hectares. The intensity of irrigation is 30 per cent for wheat and 15 per cent for rice. The kor period for wheat is 4 weeks, and for rice 3 weeks. Kor watering depths for wheat and rice are 135 mm and 190 mm, respectively. Estimate the outlet discharge. Ans: 1.674 cumecs Solution: We know, Duty (in hectares/cumec): B D = 8.64 ∆ where, B is in days, ∆ is depth in meters. For rice, 3× 7 D = 8.64 0.19 = 954.95 hectares/cumec Cultivated area = Irrigation Intensity × CCA = 0.15 × 10000 = 1500 hectares 1500 Discharge required = 954.95 = 1.571 m3/s For wheat, 4× 7 D = 8.64 0.135 = 1792 hectares/cumec Cultivated area = Irrigation Intensity × CCA = 0.3 × 10000 = 3000 hectares 3000 Discharge required = 1792 = 1.674 m3/s Here, both crops are in different season, so highest governs the discharge (In case some crops overlap and the sum of both governs discharge). So, required outlet discharge is 1.674 m3/s.  Soil Moisture Relation The water above water table is termed as soil-moisture while below as groundwater. Root zone depth: Maximum depth in soil strata upto which crops spreads its roots to extract water is called as root zone depth. excess and deficit affect crop growth and yield Soil Moisture Relation  Soil Moisture Relation Gravity water: The part of rainfall or irrigated water that flows down to water table under the action of gravity. Also called as super fluous water Not available for plant Capillary water: Water held by surface tension against gravity that can be extracted by plants by capillary action. This water is available for plant Also called as available water Hygroscopic water: This water is held as thin film layer on soil surface by loose chemical bond and hence is not available to plants Also called as adsorbed water Saturation Capacity: The water content of soil when all the pores are filled with water. It is the maximum water holding capacity of soil in root zone. Field Capacity: The water which cannot be drained under the action of gravity and is retained on surface of soil grain by molecular attraction or loose chemical bond(adsorption) 𝑊𝑡.𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑟𝑒𝑡𝑎𝑖𝑛𝑒𝑑 𝑖𝑛 𝑐𝑒𝑟𝑡𝑎𝑖𝑛 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑖𝑙 FC = 𝑊𝑡.𝑜𝑓 𝑠𝑎𝑚𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙  Permanent wilting point(PWP): The water content at which plant can no longer extract sufficient water for its growth and will die. Available moisture content(AMC): Difference of water content between field capacity and permanent wilting point Readily available moisture content(RAM): The portion of AMC that is most easily extracted by plants is called RAM. It is generally taken as 75% to 80% of AMC Optimum moisture content (OMC): Maximum water level upto which Moisture may be allowed to be depleted in root zone. Soil moisture deficiency: Water required to bring soil at a given water content to its field capacity. If D be the root zone depth in meters and d be the equivalent depth of water in the soil of surface area A m2 Then, 𝑊𝑡.𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑟𝑒𝑡𝑎𝑖𝑛𝑒𝑑 𝑖𝑛 𝑐𝑒𝑟𝑡𝑎𝑖𝑛 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑖𝑙 FC = 𝑊𝑡.𝑜𝑓 𝑠𝑎𝑚𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙 Let, γd = dry unit weight of soil (KN/m3) γ𝑤∗𝐴∗𝑑 FC = γ𝑑∗𝐴∗𝐷 γ𝑑∗𝐷∗𝐹𝐶 d= γ𝑤 This is depth of water stored in the soil upto root field capacity  Depth and frequency of irrigation Depth of irrigation required to increase moisture content from optimum moisture content to field capacity is given by γ𝑑∗𝐷∗(𝐹𝐶−OMC) depth of water required (d)= mm γ𝑤 Water required by plants = ETcrop mm/day 𝐷𝑒𝑝𝑡ℎ 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 Thus, Irrigation interval = ETcrop Time interval between two consecutive watering is called as frequency of irrigation (FOI) or Rotation period  Irrigation efficiencies 1. Water conveyance efficiency (ηc) – Ratio of water delivered to the fields to the water diverted into can 𝑊𝑓 ηc = ∗ 100 𝑊𝑐 Water application efficiency(ηa)- Ratio of the quantity of water stored in the root zone of the plants to the quantity of water delivered to the field. 𝑊𝑠rz ηa = ∗ 100 𝑊𝑓 Water use efficiency(ηu)- Ratio of quantity of water beneficially used by plant to the quantity of water delivered to the field. 𝑊𝑢 ηu= ∗ 100 𝑊𝑓  Irrigation efficiencies Water storage efficiency (η𝑠 ) – Ratio of water stored in the root zone during irrigation to the quantity of water required in root zone 𝑊𝑠𝑟𝑧 η𝑠 = ∗ 100 𝑊𝑟𝑟𝑧 Water distribution efficiency(η𝑑 )- Uniformity coefficient. Measures effectiveness of irrigation. It evaluates the extent to which water is uniformly distributed. d η𝑑 =(1 − ∗ 100 ) D d=average numerical deviation in depth of water stored D=average depth of water stored in field  Crop Water Requirement Quantity of water required by the crop from the time it is shown to time it is harvested is called as crop water requirement. Factors affecting crop water requirement are climate, type of soil, effective rainfall etc Consumptive Use(Cu): Total amount of water used by the plants in transpiration (building plant tissue) and evaporation form plant adjoining area in any specified duration of time. Unit mm/day Cu = Evapotranspiration + water used in plant metabolism Cu= Evapotranspiration ( Neglecting water used in plant metabolism ) Effective rainfall (Re): Rainfall during crop growing period which is available to meet the consumptive use requirement of the plant Irrigation water requirement: The amount of water to be supplied artificially by irrigation for Fulfilling crop water requirement. Irrigation Water Requirement = Crop water requirement + Losses  Consumptive Irrigation Requirement (CIR) It is the quantity of water actually required by plant. If natural rainfall provides a part of consumptive use, the consumptive irrigation requirement is given as: CIR = Cu - Re Cu= Consumptive Use, Re = Effective Rainfall Net Irrigation Requirement (NIR) In addition to CIR, NIR takes into consideration of leaching requirement as well as pre sowing requirement. NIR = CIR + LR + PSR + NWR where, LR = Leaching requirement PSR = Pre-sowing requirement NWR = Nursery water requirement  Field Irrigation Requirement (FIR) In addition to NIR, FIR takes into consideration of water application loss i.e amount of water lost as surface runoff and through deep percolation. FIR = NIR + Application Losses NIR FIR= ηa ηa = Water application efficiency Field Irrigation Requirement (FIR) In addition to FIR, GIR takes into consideration of water conveyance loss through canal system by evaporation and seepage. GIR = FIR + Conveyance Losses FIR GIR= ηc ηc = Water conveyance efficiency Q) Calculate the storage capacity of soil, depth of water available for consumptive use and irrigation interval with given data. Field Capacity = 40%, Permanent Wilting Point = 16%, Effective depth of root zone = 70 cm , Dry Density of Soil = 1.5 gm/cc , Consumptive Use of Water , ETc = 5mm/day , RAM = 80% of available moisture Ans: storage = 25.2 cm , RAM Depth = 20.16 cm and Irrigation interval = 40 days (Q) A field having 40 ha area receives supply at the rate of 8 cumecs for 6 hours and 30 cm water was stored in the rootzone. Find the water application efficiency. Ans: 70%