Clark County Pond Sample Clauses

Clark County Pond. In November, 2000 a flood test was performed at a storm-water infiltration pond in Clark County. The pond, which is shown in Figure 4.2, is located in a residential area in the northern part of Vancouver. The pond is enclosed with a chain-link fence. No information was available regarding the age of the pond or area of the basin that drains into the pond. The pond bottom is rectangular with dimensions 75 feet by 25 feet (23 meters by

Clark County Pond. The basic data that were used to estimate infiltration rates at the Clark County site are shown in Table 4.1 and in Figure 4.6. Table 4.1 lists the flow rates, the duration of the test, and the pond geometry. Figure 4.6 shows the depth of water as a function of time, measured at 10-minute intervals. The flow rate into the pond during the filling portion of the test was approximately 2000 ft3/hr (250 gpm or 57 m3/hr), and the filling stage lasted for approximately 2.5 hours. The water level in the pond reached a depth of approximately 21 inches (53 cm) during the filling portion of the test. The draining phase, which lasted just under 70 hours, can be divided into two parts. During the first part, which lasted until hour 30, the change in water level followed an exponentially shaped curve that became flatter with time. Between hour 30 and the end of the test, the water level followed a linearly shaped curve with a slope that was essentially constant. The water level data shown in Figure 4.6 can be used to estimate the infiltration rate as a function of time with Equation 4.4. Figure 4.7 shows the infiltration rate averaged over each 30-minute period. The infiltration rate increased with time during the filling portion of the test and reached a maximum rate of approximately 2 in/hr (1.4x10-3 cm/s). After the discharge to the pond was stopped, the infiltration rate quickly decreased to approximately 0.25 in/hr (1.8x10-4 cm/s). This rate remained roughly constant for the duration of the test. The total volume of water that was discharged to the infiltration pond during the full-scale test at the Clark County site was approximately 4710 ft3 (133 m3). All of this water eventually infiltrated into the ground. Figure 4.8 shows the fraction of the total inflow that had infiltrated from the pond as a function of time. The total inflow is estimated by summing the infiltration rates shown in Figure 4.7 over the duration of the test. This total inflow is given in the last column of Table 4.1. Note that the total inflow that was calculated on the basis of estimated infiltration rates (Column "I" in Table 4.1) is different from the total inflow that was calculated on the basis of discharge to the pond