HomeMy WebLinkAboutCC - Engineers Drainage Calcs Kimley>>>Horn
MEMORANDUM
From: Michael O'Reilly, PE
Kimley-Horn
Date: 4/11/2025
Subject: District Ten Mile Subdivision 1 Drainage Calculations
This memo accompanies the submittal of the public improvements plans for the District Ten Mile
Subdivision.
The proposed improvements are the public utility improvements and access road required for access
and utility services to each of the proposed lots. The proposed access road is the only impervious
area proposed as part of the improvements. To treat the additional runoff generated from the
proposed road, a drainage swale has been proposed on either side of the road. A section for this
swale can be seen on Sheet C7.00 of the construction drawings. The proposed drainage swale has a
9' top width, 1' bottom width, and side slopes of 3:1. This provides 5.83 cf of storage per linear foot of
roadway with 0.5' of freeboard. Using Ada County Highway District's stormwater requirements, the
100-yr rainfall event would require 2.2 cf per linear foot of the access road. Therefore the proposed
drainage swales have more than enough capacity to handle the increased stormwater from the
access road.
Therefore, it is our opinion that the proposed drainage management is sufficient for the interim
condition for the plat improvements. Once each lot develops then the lot will have to retain it's portion
of the roadway in a final design that is acceptable to the City of Meridian.
Please let us know if you have any questions or need any additional information. Thank you!