جستجوی مقالات مرتبط با کلیدواژه « irrigation canals » در نشریات گروه « مکانیزاسیون کشاورزی »

Concrete is the most common material used to line irrigation canals and must maintain its durability for the lifetime of the canal. Compressive strength has been used as an index to control the quality of concrete; concrete that remains durable under freeze-thaw conditions is that with high compressive strength. Research has shown that concrete linings can show suitable compressive strength in the first days of existence, but begin to decompose after a period and lose the property of durability. The present study examined the relationship between compressive strength and the durability parameters of initial water absorption, final water absorption, water penetration depth and porosity in the Variyaneh and Dingel-e Kahriz irrigation canals in the province of Hamedan. Laboratory testing was carried out on 27 cores (69 mm in diameter; different lengths) extracted from the concrete linings of canals. The cores were prepared and their compressive strength and durability parameters were determined. The results show an inverse linear relationship between the compressive strength and density of the samples and their porosity. The durability parameters of initial water absorption, final water absorption, and water penetration depth showed no significant relationship. The results indicate that compressive strength is not sufficient for evaluation of the durability of concrete lining. Of the 27 cores, 40% had acceptable compressive strength. Of these, 50% showed acceptable durability parameters for exposure to freeze-thaw. The results also showed that the mean penetration depth and porosity of the samples were >2.5 timesgreater than the maximum recommended values and that the initial and total water absorption values were >1.5 times greater than the maximum recommended values. It is evident that the concrete linings will decompose more quickly than the anticipated lifetime from the influence of water and other expansive solute solutions in cold weather. It was noted that samples having similar compressive strengths had durability parameters that were greater or less than acceptable values. These results suggest that the compressive strength of concrete alone is insufficient to ensure durability and it is necessary to examine additional parameters affecting the lifetime of the concrete linings.

The conjunctive use of surface and groundwater in irrigation networks influences the performance of canals. One condition of conjunctive use is to add the groundwater to the surface water via a canal to satisfy demand. Management and operation of the canal is a complex task that must consider demand variation and groundwater entering the canal. The variety of decision variables in conjunctive use requires the use of optimization techniques to determine optimal operation. Simulation models should be combinedwith optimization models for this purpose. In this research, an irrigation conveyance system simulation (ICSS) hydrodynamic model was used to simulate the flow in an irrigation canal. A combined optimization technique was used that considered the complex and implicit relations between the objective function anddecision variables. A model based on the shuffled complex evolution (SCE) optimization technique, a heuristic intelligent search technique, was used to develop an ICSS-SCE model. The proposed model was applied to the L8 canal of the Qazvin irrigation network, consisting of five conjunctive wells. Two options (25 and 40%) for demand increase provided by groundwater was considered. For each option, regular and optimum operations (four options in total) were taken into account. Optimal control settings (for water flow) were determined and canal performance for each option was calculated using the ICSS-SCE model.The results showed that setting controls according to optimal recommendations influenced by conjunctive use led to considerable performance improvement of the canal and intakes. The objective function of the canal was improved in two cases by 40-48%. In general, it was concluded that the proposed model was capable of determining optimal operation of the irrigation canals under conjunctive surface and groundwater use.