HomeMy WebLinkAboutFile Documents.395 Thunderbowl Ln.0153.2017 (67).ARBKWoody Creek Engineering, LLC
PO Box 575
Woody Creek, CO 81656
970.429.8297 (o)
970.309.7130 (c)
395 Thunderbowl Lane MEMO Asbuilt Drainage 20210204
Memorandum
To: Engineering Staff
From: Josh Rice, P.E.
CC:
WCE Project
Number: 0049
Date: February 4, 2021
Re: 395 Thunderbowl Lane As-built Drainage Analysis
The drainage system was generally built per plan except for Pipe A (Western Main), the East Pond Outlet
and the size of the ponds. We have analyzed Pipe A minimum conveyance capacities versus required ca-
pacities. We have revised the orifice based on the as-built storage condition. With the change to the ori-
fice plate, the as-built drainage system operates as designed.
1. Pipe A Capacity:
Pipe A was required to convey 0.837 cfs per the approved drainage report (see Table 5 in the ap-
proved report). The minimum pipe slope as depicted by the as-built survey is a 6” PVC @ 1.32%
(see Figure 1 for calculation). The pipe has a carrying capacity of 0.91 cfs when flowing 80%
full.
2. Storage
A total of 450 cf of storage was constructed. The drainage report required 340 cf.
3. Outlet Orifice
A 4.83” diameter orifice plate limits the release from the sand filter to the report approved allow-
able release rate of 1.002 cfs (see Figure 2 for calculation).
1/11/20182/4/2021
Page 2
February 4, 2021
Re: 395 Thunderbowl Lane As-built Drainage Analysis
395 Thunderbowl Lane MEMO Asbuilt Drainage 20210204
Figure 1. Pipe A Capacity
Page 3
February 4, 2021
Re: 395 Thunderbowl Lane As-built Drainage Analysis
395 Thunderbowl Lane MEMO Asbuilt Drainage 20210204
Figure 2. Bioretention Orifice Calculation