Rainwater Harvesting at the NAU ARD Building


The ARD Team

Porject Description

Design Process

Site Location

Precipitation Analysis

Water Consumption

Rooftop Analysis

Sizing and Location

Water Distribution

Applicable Regulations



Applicable Regulations


The main purpose for installing a rainwater harvesting system at the Applied Research and Development building is to provide water for an urban garden that will be built on the top two tiers of the runoff detention basin on the south side of the building.  This basin serves a large portion of the west side of flagstaff in capturing rainwater runoff from large storms and snowmelt.  It is also an area designated for storing excess snow removed from roadways.  Because of the effort to beautify this formerly neglected portion of campus, it is important to look at pertinent laws and regulations that might affect these plans.

Terracing the Rainwater Basin

As a part of the original landscaping plan, the different levels of the detention basin were to be terraced using rock to represent the rock face of the Grand Canyon.  This has been a reoccurring theme throughout the process of brainstorming a design for the landscaping of the basin.  In order to make this work there are some considerations that need to be addressed with regards to the intended use of the detention basin.  One requirement is that any changes do not decrease the volume of the detention basin.  This includes terracing the basin, as well as the addition of planting beds for the garden.  Another requirement is that large equipment such as earth movers be able to access the detention basin.  This means that terracing 360° around the basin would not be a practical design aspect.  Also, with regards to the gardening area, the maximum allowed height of a retaining wall is five feet, and the minimum width between retaining walls is three feet.  A retaining wall greater than four feet tall should have a guard rail for safety purposes.

Water Rights Issues

The use of a garden in the detention basin means that a small amount of water will be released into the basin area through infiltration.  This small amount of water will not have any effect on the ability of the runoff detention basin to function normally, and does not cause conflict with the city with regards to water rights issues.  The collection of rainwater from the roof of the ARD building is also not an issue for concern.  This water can be collected freely without a claim from the city.  The rainwater and runoff that is collected in the detention basin, however, does belong to the city and should not be removed.


The City of Flagstaff codes do not present any obstacle in the rehabilitation of the rainwater detention basin and its use for urban gardening.  Because the volume of the detention basin must be maintained it is recommended that the top two levels of the garden be terraced using cut and fill as opposed to building raised beds in the detention pond.  It is also recommended that some type of access for large equipment be maintained as part of the design.  The retaining walls for the gardening are should also be built less than three feet in height to avoid the need for rails and address safety concerns.