Irrigation planning using geographic information system
Authors: Muthanna Gawaher , Amin M.S.M. 
Published: January 2007

Purpose

The purpose of this paper is to present a procedure to estimate the total irrigation water requirement for a command area of 2,500 hectares in an arid environment under various crops and soil types using GIS for data storage, analysis and visualization of results.

Design/methodology/approach

Bani Al‐Harith agricultural area in Sana'a basin, Yemen was chosen for the study. ArcView GIS was used to plan for suitable crops and estimate the irrigation water requirements based on the farmer's preference and soil types. Using the available soil maps, the soil characteristics such as salinity, texture and suitable crop types were overlaid to produce the crop blocks map. The water balance equation was used to produce the crop water requirement map considering the crop coefficient for different crop stages. The total water demand for each irrigation block was calculated by summing the three components, namely percolation loss through the soil, maximum evapotranspiration of the crop and leaching requirement (LR) to maintain an acceptable salinity level.

Findings

The case study is an example of using GIS as an effective tool in irrigation planning. GIS facilities to acquire, store, analyze and display spatial data were used to produce the soil class map, soil profile map, crop map and water requirement map. The profile ECe values for the chosen crops is within the crop salinity tolerance for 100 percent yield except for blocks 4 and 5 where grape and coffee respectively are suggested to be grown. The profile ECe values are 18.37 dS/m in block 4 and 3.27 to 7.88 dS/m in block 5. The tolerance threshold of 100 percent yield for grape is 1.5 dS/m and for coffee is 3 to 6 dS/m. The salinity of the irrigation water was 2.08 dS/m. From the crop blocks map, the salinity tolerance level for 100 percent yield of onion for block 1 is 1.2 dS/m, tomato for block 2 is 2.5 dS/m, alfalfa for block 3 is 2 dS/m, grape for block 4 is 1.5/ dS/m, and the salinity tolerance level for 100 percent yield of coffee for block 5 is 5 dS/m. Leaching requirements were obtained by taking ECw value of 2.08 and ECe of 1.2, 2.5, 2, 1.5 and 5 for onion, tomato, alfalfa, grape and coffee respectively. The peak total water requirement occurred in May and was found to be 5,595 m3/ha, or 560 mm. The design irrigation water requirement for every block is shown in a map for easy visualization and manipulation to produce the best combination of soils, crops and water use.

Research limitations/implications

This method of determining the total irrigation water requirement is dependent on the selected irrigation system and crops whether shallow‐rooted, deep‐rooted or tree crops. The use of water in agriculture should be judicious, precise and sustainable. Application of GIS can be a useful tool in irrigation management since it provides rapid access to underlying information of crop suitability. The designer can try out various combinations of crops, to suit the soils and available water.

Practical implications

This methodology is useful for training irrigation engineers and water resource planners on the use of GIS technique to plan irrigation projects in arid areas.

Originality/value

This technique has never been applied to the study area.