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Development of a model for dam irrigation management based on GIS network models
Abolghasem Chehreghani, Saadi Mesgari, Mohammad Karimi, Ahmad Seyfi Mastan
Department of GIS, Faculty of Geodesy & Geomathics
K.N.Toosi University, Tehran, Iran
Abstract
As a result of population growth and industry development, the consumption of water increases continuously. A large portion of usable water is consumed by agriculture, which requires more efficient ways for both conveyances of water and irrigation. Usually the efficiency of irrigation-water conveyance is too low, meaning that much of the water is either evaporated or absorbed by soil before reaching the user. In this paper, we describe the development of a model for the management of dam-irrigation network. The model is on the basis of network analysis /modeling capabilities of GIS. In this model, the water conveyance efficiency of every segment and consequently every route on the network is calculated. Having the amount of water by farmers on lands, the amount of water needed to be entered to the network is computed. Then, we can compare the whole amount of water needed to be provided with the amount obtainable from the dam discharge. These, in turn, could be used to plan and ration the consumption of water by users and to classify farms according to their priorities for irrigation in an irrigation network.
1. Introduction
The amount of available water resources for irrigation decreases continuously. The reasons for this include population growth, industrial development and global climate changes. According to the available census, agriculture as the main consumer of water uses 92 percent of the 93.1 billion cubic-meter available water (Irani, K.S., 2004).
Agriculture is not only the largest water consumer, but also it uses water with the cheapest price and lowest efficiency (Irani, K.S., 2004). Previous studies in many countries show that the low efficiency of the irrigation systems is mostly the result of weak maintenance and management of irrigation network. This is the main obstacle to the justly consumption of water among farmers. That is, further farms from the water source get much less water than the nearer ones (Irani, K.S., 2004).
The issue of water saving, after a certain point, is that of water saving in irrigation. Thus, irrigated agriculture is increasingly feeling the pressure to demonstrate and improve its performance (Burt, C.M., A.J.Clemmens, T.S.Strelkoff et al., 1997).
In this article a method on the basis of the network analysis capabilities of GIS is described to help in a better management of the irrigation network.
2. Modeling of the irrigation network spatial features
Usually there are five types of features in an irrigation network:
- Dam: this is the provider of water to the irrigation system. It can be presented as a point feature having the name, the ID and the amount of water delivery as its attributes.
- Channels: they act as the transporter of water to the farms and are divided into three groups(Khuzestan's energy organization, 2000):
- Level-one channel, that receives water from dam and sends it to level-two channels or to other level-one branches;
- Level-two channel, starts from a level-one and transfers water to level-three channels;
- Channels of level three and four are the branches of the network that deliver the water to individual or groups of farms.
The name and identifier of the channel, its water capacity, the ids of its start and end gates are the attributes that should be linked to channel features.
- Gates/Turnouts: through these features, the water is delivered from higher level channels to the lower level ones. At the end of level-four channels also, the farms receive the water from the farm turnouts. These features are represented as points, having the attributes of ID and the amount of water received (capacity).
- Lands (villages): the main purpose of irrigation network is to transfer water from the sources to these features. When the data about each land is not available, the village could be considered instead. These features are modeled by points. Regarding each cultivation type present at a village, the attributes of cultivation type area and percentage to the whole cultivation of the village are linked to the village.
- Consumption points: the farm turnouts are the consumption points. These points are required to be connected to the villages. The purpose of the irrigation system is to serve these points.
- Other consumers: beside agriculture, usually there are other types of consumers. Name of the feature and its consumption are the main attributes.
- The table of needs for water: this is the only non-spatial part of the model that is connected to consumption points (villages). In this table, the amount of needed water for each cultivation type in area unit is recorded.
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