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disruptive to the existing landscape. To maximize pipe flow potential and limit head build up,a <br /> 24"arch pipe was assumed for cost estimating purposes. <br /> This was an option originally considered in the preliminary analysis. Once the survey data was <br /> obtained it was recognized that this may not be a viable alternative. Because the invert of an <br /> emergency overflow pipe at the east end of the driveway would be higher than the low garage <br /> floor elevations,this option would not serve a practical purpose. Modeling Option 2 showed <br /> that this action would have no impact on either the north or south low points. The estimated <br /> cost for Option 2 is shown in Table 1. <br /> Option 3(Figure 4) <br /> Option 3 would serve to isolate the low point catch basins on Arden View Court from the main <br /> line storm sewer. A 24"storm sewer bypass pipe would be constructed between units 4401 and <br /> 4402 of Arden View Court. <br /> Currently,the entire flow upstream of the low point catch basins in Arden View Court must <br /> make a 90-degree turn at the catch basin to continue downstream. Given the momentum and <br /> velocity of a 24"pipe flowing full,it is likely that the storm sewer pipe and grate in the <br /> driveway to the east of this low point is surcharged and backs up during heavy rainfall events, <br /> as occurred in July of 2011. It was thought that a proposed bypass pipe would help to relieve <br /> flow pressure from the low point in Arden View Court and likely reduce the flooding potential <br /> in this area. To minimize disruption to the existing landscape in this area,a new pipe was <br /> considered to be jacked. <br /> Modeling Option 3 showed insignificant improvement to either the north or south low points. <br /> The HWL at the north low point was 973.33(-0.02')and the HWL at the south low point was <br /> 964.98 (-0.17'). The estimated cost for this improvement is shown in Table 1. <br /> Option 4(Figure 5) <br /> This option involves constructing a new outlet from Pond 2 towards the west,which would <br /> outlet near Pond 5. A new outlet pipe from Pond 2 would reduce the outflow from the <br /> downstream storm sewer conveyance system. This would provide extra carrying capacity of <br /> the existing system,thus allowing for greater storm events to be handled before surcharging <br /> occurred. A directionally drilled pipe from Pond 2 towards Pond 5 would limit the overland <br /> disruption. <br /> Modeling Option 4 showed no significant improvements at either low point. The HWL at the <br /> north point was 973.29(-0.06')and the HWL at the south low point was 965.09(-0.06'). The <br /> estimated cost for this improvement is shown in Table 1. <br /> Option 5(Figure 6) <br /> This option focused on reducing the flooding in the southern low point and is similar to Option <br /> 2. The difference is that a new storm sewer outlet was simulated being constructed near the <br /> existing rectangular driveway grate,which is east of the south low point on Arden View Court. <br /> This pipe system was routed toward the southeast pond(Pond 3),where it would outlet. This <br /> scenario placed a new grate near the existing low point,which could start taking water <br /> immediately once runoff from the catchment occurred and divert some of this flow to the <br /> southeast. <br /> This scenario was modeled simulating the July,2011 storm,with the existing low point catch <br /> basins in this area essentially plugged. Constructing a new catch basin structure and a 24" <br /> outlet pipe resulted in a HWL of 966.4 at the southern low point. The existing low garage <br /> elevation is 966.63. This option would protect the low townhomes adjacent to the low point <br />