Fig.1. Experimental Setup for horizontal infiltration Theoretical back ground A well-known equation for water conservation is defined to analyze the dynamic water flow during the infiltration process. This equation is shown in Eq. (1) (1) where is the soil water content (SWC), is the water inflow to the soil, Jwi θ(t) is the density of water, is the volume of water entry to the soil, and are the V water losses from the soil system caused by the soil evaporation and the plant transpiration, which does not contain in our experiment. For linear time invariant (LTI) systems, the transfer function models are introduced to denote dynamic responses between selected inputs and outputs of the physical system. These modeling are used extensively in the field of control system design because it is often the most effective way to incorporate LTI other elements in otherwise physical computational model (Franklin et al., 1998). In our transfer function modeling, the first order transfer function of G(s) was used: where is the gain constant, is the time constant, and is the time lag. The Kp step response of for the input of the water head is given by: h(t) θ(t) (3) where is obtained from the inverse Laplace transform using Eq. (2), is the ) θ(t) Heaviside function which is equal to 1 within and 0 at other time, is the value of the step function. RESULTS & DISCUSSIONS Figure 2 shows the experimental matric potential and the volumetric water content curves for the Karma clay soil. The curve has a point of inflection. In Fig. 2.the SWC gradient is changed at = -230 cmH2O and increases from this Ψm point. Figure 3 shows the transient response of SWC and the matric potential. As can be observed, when the infiltration starts, SWC increases from the initial value 10 % associated with the negative matric potential decrease from the maximal value -70kpa. After about 4 hours, SWC approaches to the saturated value 45%. The negative matric potential changes at about 2 hours when SWC is about 30%,
Fig.1. Experimental Setup for horizontal infiltration Theoretical back ground A well-known equation for water conservation is defined to analyze the dynamic water flow during the infiltration process. This equation is shown in Eq. (1) (1) where θ(t) is the soil water content (SWC), Jwi is the water inflow to the soil, is the density of water, V is the volume of water entry to the soil, and are the water losses from the soil system caused by the soil evaporation and the plant transpiration, which does not contain in our experiment. For linear time invariant (LTI) systems, the transfer function models are introduced to denote dynamic responses between selected inputs and outputs of the physical system. These modeling are used extensively in the field of control system design because it is often the most effective way to incorporate LTI other elements in otherwise physical computational model (Franklin et al., 1998). In our transfer function modeling, the first order transfer function of G(s) was used: where Kp is the gain constant, is the time constant, and is the time lag. The step response of θ(t) for the input of the water head h(t) is given by: (3) where θ(t) is obtained from the inverse Laplace transform using Eq. (2), ) is the Heaviside function which is equal to 1 within and 0 at other time, is the value of the step function. RESULTS & DISCUSSIONS Figure 2 shows the experimental matric potential and the volumetric water content curves for the Karma clay soil. The curve has a point of inflection. In Fig. 2.the SWC gradient is changed at Ψm = -230 cmH2O and increases from this point. Figure 3 shows the transient response of SWC and the matric potential. As can be observed, when the infiltration starts, SWC increases from the initial value 10 % associated with the negative matric potential decrease from the maximal value -70kpa. After about 4 hours, SWC approaches to the saturated value 45%. The negative matric potential changes at about 2 hours when SWC is about 30%,
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