7805 40TH AVE W 2018 Plans 2022-11-30 (2)

0 above from entering the detention and water treatment system.This change also results in some of the flow from the frontage improvements bypassing the detention system instead of entering the detention system as is intended,however as noted,the additional existing road water offsets this water that is being bypassed.The discussion above,and the calculation provided in the following section,show that the excess flow from the existing roadway that is going into CB#2,and should instead be bypassing the detention system,is offset by the flow at the frontage that will be bypassing the detention system by the revision to CB#7 so the net effect is that the drainage code is being met. Supporting Calculation The calculation presented in this section shows that the area of frontage flow that is bypassing the detention system is offset by the area of additional flow from the existing road that is now being picked- up and is going through the detention system. In Figure 2 below,the orange shaded area labeled A approximates the flow from the existing road that collects at CB#2 and the teal shaded area labeled B approximates the flow from the frontage improvements that collects at the proposed location for CB#7. These areas are depicted based on field observations during rainfall events and considering the as-built geometry of the roadway.As mentioned previously,the roadway has a 6.4%grade and a 2%cross slope with the crown at the middle of the roadway. It is noted that the pre-construction contour lines shown on drawing C3.0 do not show the location of the as-built crown correctly as observed in the field. Water will flow along the longer,steeper slope more quickly than the cross slope which has resulted in the existing original report identified bypass flows,bypassing CB#6.The Area A depiction of additional road flow that is going into the detention system,and being treated has been terminated just south of the southern property line as the goal of this calculation is to show that there is more than sufficient flow area from the existing road going to CB#2 that was not included in the original calculations to offset the flow at the frontage area that is now going into CB#7. In reality based on as-built field observations,a larger portion of the 2.03 acres of upstream flow bypasses the bypass collection system and collects at the low point of the roadway profile than was originally modeled.As a result the revised location of CB#7 into the road with an open grate,does the job of what CB#6 was originally designed to do,and that is to collect the upstream flow to be bypassed.The additional area that bypasses both CBs shown as area A,collects and goes through the detention and water treatment system so the overall requirement of treating the equivalent of the new area is being accomplished and the drainage code being met through CB#2.