Narrative
Water, Civil, and Environmental Inc. TMCC Bridge Installation
February 28, 2020 Narrative
To: City of Meridian Project: Private Bridge Installation
Prepared By:
Ryan a. Eldridge, P.E.
Cc: File
Date: April 17, 2020 Task:
Subject: Narrative for Proposed Bridge installation for Ten Mile Christian Church
Introduction:
Water, Civil, and Environmental Inc. (WCE Inc.) has prepared this narrative for the installation of a private
bridge that crosses Ten Mile Creek at Ada County Parcel Numbers S1210449033 and S1210449070. The
bridge will be used by Ten Mile Cristian Church to gain vehicular access to their property on east side of
Ten Mile Creek.
Background
Ten Mile Christian Church (TMCC) owns two parcels of land that are currently segregated by a section of
Ten Mile Creek that they would like connected. TMCC is proposing to construct a bridge and abutments to
gain vehicular access to their property on the northeast side of Ten Mile Creek. Elements for this project
include installation of a new prefabricated steel bridge with supersill abutments and construction of a short
span of road. The bridge and abutments are being designed to span from top of bank to top of bank outside
the flow path of 10 Mile Creek. No construction within the banks of 10 Mile Creek is anticipated for this
project.
Project Area
Ten Mile Creek runs along the north side of Ada County, Idaho Parcel Number S1210449033. The proposed
bridge crosses the river on the northeast edge of the parcel at the following approximate coordinates:
• Latitude = 43.606714o N and Longitude 116.434901°W
The parcel is located on FEMA Map Number 16001C0231H; a FEMA Firmette of the study area is attached.
Elevation Data Sources
Detailed topographic data and cross sections were collected by Forsgren Associates Inc. in May, 2019. This
survey data is referenced to NAD83 Idaho State Planes, West Zone.
Description of the Proposed Bridge
The proposed bridge is a 28’ x 80’ pre-engineered modular steel bridge with supersill abutments on either
side of Ten Mile Creek. The proposed bridge will consist of the following elements:
Water, Civil, and Environmental Inc. TMCC Bridge Installation
April 17, 2020 Narrative
• SuperSill Abutments
• W-Beam steel girders
• Steel deck surface with concrete wearing surface
• Weathering steel w-beam guard rail
• Grading of the bridge approaches
The proposed bridge will be constructed so that the installation and use of the bridge will not impact the
channel’s natural flow for a 100-year flood, as shown in drawing sheet C103. To minimize impact to Ten
Mile Creek, all construction of roadways and installation of the bridge will occur outside and away from
the 100 year floodway for Ten Mile Creek. The use of an erosion and sediment control (ESC) plan, drawing
sheets ESC01 and ESC02, and best management practices will then ensure no impact to Ten Mile Creek.
Description of the Proposed Driveways
The installation of approximately 200 feet of gravel driveway on the west side of the canal and 220 feet of
asphalt driveway on east side of the canal is proposed for this project. The gravel driveway will be installed
from the gravel overflow parking in front of Ten Mile Christian Church and will be graded to a short, 40
foot section of asphalt road that will be connected to the bridge. The east side of the bridge will be connected
to an existing parking lot in parcel # S1210449070 by a 180-foot-long asphalt driveway. Driveway plan and
profile drawings can be found in drawing sheet C102.
Hydrology
A No-Rise report has been prepared to provide the city of Meridian with the information needed to confirm
that the proposed project meets both its own and FEMA’s no-rise requirements. FEMA guidelines state that
the effective FEMA hydraulic model is the primary tool that should be used to demonstrate “No -Rise”.
However, at this time, FEMA has not conducted a detailed hydraulic analysis along Ten Mile Creek in the
proximity of the proposed bridge replacement and only an estimated floodway has been developed and
published by FEMA. Since a specific BFE has not been established for the study area, FEMA regulations
44CFR 60.3 (b) were followed and, utilizing the FIS 100-yr event from Flood Insurance Study – Ada
County, Idaho and Incorporated Areas (FEMA, Revised 2003), survey data, and United States Army Corps
of Engineers’ HEC-RAS modeling software, a BFE condition was established and employed. Model results
demonstrate that the project will not increase 100-year floodplain or floodway water surface elevation and
therefore satisfies the “No-Rise” requirement.
Conclusion
The existing and proposed conditions model shows that during a 100-year flood event, the water level in
the channel is such that it will be contained in the channel. The project will not alter the channel at or below
the 100 yr flood BFE with all construction and installation occurring outside and away from said BFE. The
bridge and abutments will be located above and outside the 100-YR flood plain. Finally, with the use of the
ESC plan and best management practices there will be no negative impact to Ten Mile Creek.