Theoretical analysis and experiment of hydrodynamics of water distributor for linear run-on infiltrometers

Abstract: The water distributor is one of the important components of the linear source method for soil infiltability measurement. This study suggested a new material and structure of the water distributor, which used special sponges to make the key component for water distribution. The water distributor was composed of a water supply tubing, a water distribution chamber, a level, a sponge strip and a fixing plate. Theoretical analysis was made to detail the requirements of an ideal water distributor for even distribution of water flow supplied to soil surface for infiltration along its length. Hydrodynamics of water movement inside the water distribution sponge along its length and those at the interface both inside the soil and the water distribution sponge were analyzed. Analysis was made on the conditions for identifying the materials for the water distributor manufacturing. Trials were made to select the sponge materials of ideal hydraulic responses before water distributors were made and used in the experiments to identify their hydrodynamic responses. A centrifuge machine was used to measure the pF-curves of the sponges, ranging from -105 Pa up to -103 Pa. The exponential function was used to fit the measured data between the water content and suction. For the ideal material chosen from the experiments, there was a good relationship between the water content and soil-water suction, with the coefficient of determination, R2=0.948. Water content remained very low and almost constant as the water potential inside the sponge increased at its low level (i.e. large negative values). After some critical value of the water potential, the water content increased very rapidly with an increase in water potential. Water potential continuity concept was used to analyze the water movement in the interface between soil surface and the water distributor. The results indicated that the sponge selected for the experiment was an ideal hydrological material for the water distributor. The details of the water distributor structures were also obtained from the study. Manufactured linear water distributors were used for actual water application under laboratory condition and the wetted area on soil surface had a very good linear pattern. The measured results verified the hydraulic characteristics analysis of water distributor and hydrodynamic data through the experiment demonstrating the feasibilities of the newly suggested linear water distributor. This study will help the application of the linear run-on method for soil infiltrability measurement and relevant to some related applications.