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In arid and semiarid regions such as the south-eastern Spain, agricultural water reservoirs for irrigation are required to regulate available water allocations adapting them to the crops demands. However, surface water storage has two major problems: (i) substantial water losses through evaporation and (ii) a high nutrient loading that induces frequent algal blooms, resulting in serious water quality problems that are of great concern for drip irrigation systems. In order to maintain the hydraulic efficiency of these systems, filtration equipment is frequently subjected to cleaning processes, which involve significant losses of water and energy.

In this water stressed region, suspended shade cloth covers are being installed on the reservoirs. These covers, made of polyethylene, significantly reduce evaporation and improve the quality of stored water.

This study evaluates the effect of the installation of suspended shade cloth covers on the filtering equipment. To carry out with the experiment, 10 agricultural water reservoirs with normal regulation of the irrigation were selected: 4 uncovered reservoirs with algaecide treatment, 4 uncovered reservoirs without algaecide treatment and 2 covered reservoirs without algaecide treatment. To perform the filtering, a portable irrigation system was designed with several analogical and digital manometers that evaluated for each test the progressive increase of the pressure drop in the filter. Additionally, chlorophyll-a (a proxy of the algae concentration) was measured in the field using a multi-parametric instrument. After each test, the filter was dried and weighed to determine the amount of retained particles and algae. In uncovered water reservoirs without algaecide treatment, filters were saturated in 0.45 to 2.25 h (water filtered = 1.7 to 8.0 m(3)). In uncovered water reservoirs with algaecide treatment, filters were saturated in 42 to 51 h (water filtered = 151 to 183 m(3)). Finally, in covered water reservoirs, filtering trials ended without reaching saturation of the filters (>450 h and >1500 m(3)).

These results indicate that the use of suspended shade cloth covers significantly reduces the filtering requirements and therefore, in an irrigation system, filtration could just be considered as a preventive process to maintain the irrigation system instead of being frequent and compulsory.