Project Information

Project Description:

The Flagstaff Family Food Bank (FFFB) is experiencing flooding damage to their property due to high intensity monsoonal rain events during July and August. Runoff Engineering, Inc.’s task is to remediate flooding issues at the FFFB by developing a design that is inexpensive and adheres to City of Flagstaff (CoF) codes and requirements.  Analysis of design alternatives will be conducted in this report and will consist of: topographical studies, hydrological studies, and an economical analysis’s.  Once design alternatives have been analyzed, a final design recommendation will be presented based on a decision matrix.

Topographical Analysis:

The topographic map aided in the analysis of natural flows of stormwater runoff, low points where ponding occurs, building locations and other permanent structures, potential cut/fill values for design alternatives, and slopes of the existing property for hydrological analysis.  From the topographic map, it was found that the slope in front of the main building contributes to the flooding issue.This creates as a ponding area for the water to form between the slope and the office, causing damages to the property.

Hydrological Analysis:

The City of Flagstaff Stormwater Management Design Manual was utilized to ensure the CoF standards and procedures for hydrologic analysis were adhered to.  From the design manual, the rational formula was implemented to calculate the flow on the FFFB property, and, the sheet flow travel time formula for the area in front of the building.  The precipitation data was gathered from NOAA Atlas 14 and the evaluation of a 10 year storm was conducted, per the City of Flagstaff Stormwater Management Design Manual.

Design Alternatives:

Design alternatives have been developed in order to assess the most effective solutions to alleviate the flooding on the FFFB property.  The main priority of the FFFB project is to eliminate the ponding and flooding that occurs near the front of the FFFB property.   Before a design alternative can be installed, the current slope at the front of the main office must be removed. This will be done by cutting out the current slope for a more favorable slope, in order to control the flow at the front of the property and to mitigate flooding. Once the surface is regraded, design alternatives can be employed. For these design alternatives, Runoff Engineering is proposing two designs: a commercial drain with retaining wall, and a valley gutter with a retaining wall.

Design Assessment:

The purpose of the FFFB project is to alleviate the flooding occurring. The client requested that more than one final design option be presented. In order to meet these demands and to ensure flexibility, Runoff Engineering did not select a final design. However, Runoff Engineering has further assessed the design options, in order to assist the client in selecting a design to best suit their needs.