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Development of a model for dam irrigation management based on GIS network models


3. Description of the model
Irrigation network efficiency is generally defined as amount of water received by consumer divided by the water taken from the source. This includes the three parts of conveyance, field canal and field application efficiency (Khuzestan's energy organization, 2000). Conveyance efficiency is related to the working condition and design of the channels, gates and penstocks. The field canal and field application efficiency depends on the irrigation channels and irrigation system used inside the farms. Therefore, these parts of efficiency are not covered in this article. Here, we calculate conveyance efficiency and call it efficiency.

To define the efficiency of the network, the efficiency of each link should be calculated and considered. To do this, the water delivered to the gate of beginning of the link and the water received at the gate of the end of link are measured. By dividing the output water to the water inputted to the link and multiplying it by 100, the efficiency of the link is extracted.

To calculate the efficiency of the network, on the basis of the shape and connections in the network, it is divided to some regions, each served and fed with a level-two channel. In each region, for every level (levels from two to four) the averages of efficiency of all links are calculated. By multiplying the efficiency averages of all three levels, the efficiency of that region is calculated.

3.1. Calculation of the efficiency The methods of calculating the efficiency of the channels are similar. To get proper formulas, we consider them in two groups of one-part channels and multi-part channels.

  • One-part channels
    Channels of level four are usually of this type. They consist of one part each. The efficiency, as mentioned, is calculated by dividing the output of the channel by its input water and multiplying it by 100; that is:



    E is the water received at the gate of the end of the channel and T is the water delivered to the gate of the beginning of the channel
  • Multi-part channel
    A channel of this type consists of many parts. In other words, in such a channel there are a few gates. Any such a gate delivers water to lower level channels. Usually channels of level one, two and three are of this type. To calculate the efficiency of such a channel, the channel is divided into simple (one-part) sections. Then for each one of simple sections, the efficiencies are calculated and then multiplied (formulas 2 and 3).





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