Determining the infiltration capacity in the unsaturated environment using the integration of the infiltration trench and the permeable pipe in the laboratory environment

Among the problems faced by artificial feeding methods, we can mention low rainfall, limited water resources, high temperature and high evaporation, high sediment yield due to poor vegetation cover, etc. Artificial feeding methods in these areas should be designed in such a way that it has maximum efficiency from the available water resources. In this research, it has been tried to reduce the aforementioned problems by presenting a new method of artificial nutrition suitable for desert areas. In order to design a suitable method of artificial nutrition, sufficient information about the distribution of water flow in the soil is needed. On the other hand, research on the distribution of water flow in porous media without modeling the field conditions is time-consuming and expensive. In the current research, the issue of determining the infiltration capacity in the unsaturated environment was discussed using the integration of the infiltration trench and the permeable pipe in the laboratory environment.

For this purpose, a physical model was built in which water was injected into the unsaturated environment through a permeable pipe and a trench. The input flow to the model included 5 flow rates of 1, 1.5, 2, 2.5 and 3 liters per minute. With the beginning of the experiment, which was entered into the model with the mentioned flow rates, the amount of progress of the moisture front was determined every 5 minutes. This process continued until the moisture front reached the water level. At the same time as the water was removed from the model, the output flows were measured every 5 minutes. The way water moves in the unsaturated environment and the formation of the moisture front was photographed and the images were analyzed using Plot Digitize and AutoCAD software. In the next step, after creating a flow in the porous medium, the volume of passing water was measured in different conditions at a certain time. The amount of water output from the model depends on factors such as the flow rate entering the model, the dimensions of the model, the slope of the ponding surface, the distance between the bottom of the trench and the ponding surface, the texture of the soil, the length of the trench, the width of the trench, the height of the permeable pipe to the bottom of the trench, the average diameter of the permeable material, and the entry time. The water depends on the model until it reaches the stagnation level and the time it takes for the water to reach the stagnation level until the end of the test. In the experiments, the input flow to the model was variable and other factors were considered fixed. After the water reaches the stagnation level in time intervals of 5 minutes for 60 minutes (a fixed time, the duration of which is obtained according to reaching the peak output flow rate from the model and preliminary tests for the lowest flow rate) It was measured for all model inlet flow rates. Next, after the completion of 60 minutes, the amount of water output from the model was measured for another 30 minutes. In flow rates of 2.5 liters per minute and 3 liters per minute, due to the fact that the inlet flow rate was higher than the capacity of the model, the excess water volume overflowed from the model. Then the inlet was cut off and for another 120 minutes, the output flow rate from the model was measured in 5 minute intervals. Then, the volume of water entering the tank (V_in) and the volume of water leaving without calculating the base flow that was mentioned earlier was measured to simulate the static level, V_out=(V_B-V_A). V_A is the volume of water input to simulate the static surface and V_B is the volume of water output from the model. The performance of the model was calculated based on V_out in relation to the volume of water coming out of the model without calculating the base flow rate as maximum 〖(V〗_(out max)) and also V_out was calculated in relation to V_in.

The highest penetration capacity of the model was determined to be 2.049 liters per minute. The results showed the trend of changes in the output flow from the model, the time the moisture front reached from the trench to the reservoir surface, the average infiltration velocity, V_out, the time to reach the maximum output flow from the model, and the slope of the water discharge line from the model after approaching the flow rate proportional to the capacity. The influence of the model has decreased. The performance of the model was evaluated based on V_out during the duration of the experiment in two modes. The best performance of the model was related to the flow rate of 2 liters per minute, which is the closest flow rate to the flow rate corresponding to the infiltration capacity of the model. The results showed that the performance at a flow rate of 2 liters per minute in the case where V_out was measured in relation to V_(out max) (water entering the model is less than the infiltration capacity of the model), 96% and in the case where V_(out max) was compared to V_in was taken into consideration (water flow entering the model is greater than the infiltration capacity of the model), its performance was determined to be 98%. In the presented artificial feeding method, the inlet flow rate through the permeable pipe should be designed according to the infiltration capacity of the trench so that the maximum capacity of the trench is used and water loss is minimized.