Training Course Conceptual irrigation design in the context of IRBM Arba Minch University, Arba Minch 26 30 March, 2012 Irrigation Improvement Options part 1- on field irrigation March 2012, Henk Ritzema
Hare Irrigation Scheme Inlet Crop
Case Study Area: Water shortage? What is causing the water shortage?
Contents Crop water requirements and irrigation scheduling Irrigation water requirements at field level Field irrigation systems Daily Water and Salt Balance Model
Irrigation: manipulating the water balance Inflow - Outflow =Change in storage (P+I) (T+E+R+D)= ±ΔS
Plant-Water-Atmosphere Movement of water due to Δ potential energy
How to calculate evapotranspiration 1. Reference Evapotranspiration (ET o ) based on climatic data 2.Crop Evapotranspiration (ET c ): ET c = k c * Et o where K c = crop coefficient, depending on crop type, crop variety and development stage
Crop coefficient K c depending on crop type, crop variety and development stage
From Crop water requirements Irrigation water requirements Soil properties affecting water flow and water storage in the soil: finer soil textures have higher water holding capacity compared to coarser soil textures, but available water depends on water holding capacity
Water holding capacity
Available Water Capacity (AWC) AWC = fc - wp where fc wp moisture content at field capacity moisture content at permanent point Soil texture Ө fc (m/m) Ө wp (m/m) AWC (m/m) Coarse sand 0.10 0.05 0.05 Sand 0.15 0.07 0.08 Loamy sand 0.18 0.07 0.11 Sandy loam 0.20 0.08 0.12 Loam 0.25 0.10 0.15 Silt loam 0.30 0.12 0.18 Silty clay loam 0.38 0.22 0.16 Clay loam 0.40 0.25 0.15 Silty clay 0.40 0.27 0.13 Clay 0.40 0.28 0.12
CROPWAT Design: crop water requirements irrigation requirements Management: irrigation schedules scheme water supply for varying crop patterns. Evaluation: farmers irrigation practices crop performance under both rainfed and irrigated conditions
CROPWAT: input output INPUT: Reference Crop Evaporation (ET 0 ) using climatic data Rainfall Cropping pattern Soil type Scheduling criteria (e.g. 80 mm/14 days) OUTPUT: Reference Crop Evaporation Crop K c Effective rain Crop water requirements Exercise and or apply in Hare Irrigation Project Irrigation requirements TAM, RAM, ET c, ET c /ET max, daily soil moisture deficit, irrigation interval, irrigation losses and estimated yield reduction
Irrigation water requirements field irrigation system ET 0 ET c CWR IWR field irrigation system
Design of field irrigation system Input: IWR & AWC required water depth Soil Type Slope of field Width of furrow border Output: Length of field Flow rate Cutback time
SURDEV - Basin, border and furrow irrigation Design, operation and evaluation of basin, border and furrow irrigation
SURDEV Design of individual plot layout
SURDEV - Design of individual plot layout Matching field (physical) with operational parameters Output: length, width and slope with frequency, rate and duration
SURDEV - Evaluation operation efficiency Exercise and or apply in Hare Irrigation Project
Remember: Irrigation = manipulating the water balance To evaluate how you did this you can use: WaSIM (for Education) SWAP (for complex applications)
WaSim Daily Water and Salt Balance Model WaSim is a computer-based training package for the teaching and demonstration of issues involved in irrigation, drainage and salinity management. WaSim simulates soil water salinity relationships for designs and water management practices and environmental scenarios
SWAP - Soil, Water, Atmosphere and Plant SWAP simulates transport of water, solutes and heat in unsaturated/saturated soils at field scale level, during growing seasons and for long term time series. Used for: Education Applied Research Scenario studies http://www.swap.alterra.nl/
Application in this training course on Conceptual Irrigation design It is up to you: modelling assignments for case study area Good luck