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Decision Support System in Irrigation Water Management

Dr. A. F. M. Afzal HOSSAIN
Institute of Water Modelling, Bangladesh

Md. Zahirul Haque KHAN
Institute of Water Modelling, Bangladesh,

Sabina SADEK
Institute of WaterModelling, Bangladesh

Abstract/ Executive Summary:

A Decision Support System (DSS) for irrigation management has been developed for a pilot area of Teesta Barrage Project. The DSS has been developed in two modules namely Irrigation Demand Module and Irrigation Management Module. Each module has a mathematical model set-up running behind it. The main purpose of the irrigation demand module is to calculate the water demand for land preparation and crop. This module requires the information about soil type, land use and crop calendar, climatic condition and initial soil moisture status at the land. The second module; Irrigation Management module simulates both the water level and discharge at offtake points of irrigation canals. The main input for this module is available discharge from Canal Head Regulator (CHR) and existing water level in the canals. Through different scenario analysis, this module will suggest the manager about gate operation schedule to provide optimum irrigation based on demand and supply.

Keywords: Decision Support System (DSS), Mathematical Modelling, Irrigation Demand, Irrigation Water Supply, Gate Operation

Location:

Start Date:

End Date:

Program Area: Socio-economic and Policy

Non-commodity: GIS

Objectives:

Decision Support System (DSS) is such a tool developed for a pilot area of the project to assess irrigation demand as well as to distribute the available water rationally. The present DSS integrates hydraulics of the system and decision-making technique through mathematical modeling and Geographical Information System (GIS).

Methodology:

The conceptual understanding is very important step in developing any tool like DSS. DSS must include the main features of the system for which it will be developed. The present DSS has been developed with the understanding of irrigation practice and hydrological system of the area. The DSS has been made as separate modules as Irrigation Demand Module and Irrigation Management Module. Before providing irrigation to a land, the assessment of irrigation considering the existing land condition, cropping stage and future rainfall is prerequisite. The main purpose of the irrigation demand module is to calculate the water demand for land preparation and crop water demand for next few days for each command area. This module will also help the manager to try for different crop types, crop rotations or staggered cropping to find the optimum composition of crops. The module provides map showing the amount of water required at each of the command areas and water requirements at canals’ offtake. Considering the demand and supply situation, the primary objective of any irrigation system is to supply irrigation water as closely as possible according to the demand. From irrigation manager’s point of view, the canal system should run as closely as possible to the target water level which in turns guarantees flow diversion closer to the demand. Irrigation Management Module will provide the canal water level and discharge at specified locations under different gate operation scenarios. Irrigation Demand Module has been developed to assess irrigation water requirement. To serve the purpose a groundwater model including unsaturated zone has been set. The mathematical modelling software MIKE SHE (DHI, 2000) has been used for the purpose.
Input in Irrigation Demand Module: This module requires the information about soil type, land use and crop calendar, climatic condition and initial soil moisture status at the land. The physical properties of the different types of soil including hydraulic conductivity, capillary pressure and water content relationships are required to calculate the vertical flow through unsaturated zone. Unsaturated zone is the place from where crop takes water. It is important to have a well-defined unsaturated zone through characteristics of soil types in detail. Classification of land based on cropping pattern has to be specified. In the present DSS land classification has been made according to the command area of tertiary canals. Each command area should be linked with a crop rotation. Crop rotation allows specifying what crops are planted when. This is an important information as model will compute water demand mainly based on the crop type and its stage at the time of computation. Varying crop rotation, benefits of crop diversification and staggered cropping may be assessed. One of the most important information when calculating water demand is the climatic condition. In present DSS, user-defined option has been made for climatic data. The user will be able to select among the climatic conditions: wet, average, dry (no rainfall) and custom. The wet and average conditions will be calculated based on historical data of the period 1974 to 2000. The custom rainfall enables the user to specify the actual or forecasted rainfall. The evapotranspiration will be taken from actual field data, though from previous years.
The initial soil moisture conditions in the root zone will be critical for the crop water demand calculations. The user will be able to select among the initial moisture conditions: 15, 10 and 5cm water on the field; saturated, i.e., groundwater table at the field; average water content is equal to field capacity or wilting point or is equal to 50% deficit, i.e., in between field capacity and wilting point. In DSS, where the initial moisture condition will be very important for calculating the water demand for a 5 to 7 day period, it is crucial that the initial conditions are correct. For each soil type there are predefined values where the moisture condition is equal to the above mentioned. When the user selects a specific initial moisture condition, those values will be used.

Source of Information: International Conference on Water & Flood Management (ICWFM-2007), 12 - 14 March 2007, BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

1.

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Total Budget (Tk.) :

Achievement/Findings:

DSS is a computer-based system, which helps decision makers to utilize data and models in decision making process. It is not the DSS that determines the decision, but the water manager who will add his experience to the information from the DSS to make the decision.
The goal of DSS is to increase the effectiveness of decision making. The main uncertainties of the present DSS are the rainfall as well as the available supply have to be estimated for the period of interest. After the the analysis, the manager can select the most suitable scenario. This approach can be adopted to manage irrigation project, where no other alternatives are available for decision making.
Present DSS has been developed to enhance the overall performance of the irrigation system of a pilot area of Teesta Barrage Project. It may be possible to introduce an automated optimization routine where by the DSS simulates a number of scenarios and offers the “best” solution to the irrigation manager. In this approach, the hydraulic behaviour of the system obtained from the simulation model is to be embedded into the optimization model and the combined model determines the best operating policy under the objectives and restrictions set by the manager.
Further use of the DSS may be extended not only for managing existing irrigation projects on a day-to-day basis but may also be used by planners when designing new irrigation projects.

Knowledge Management: Report/Proceedings