Building a fire retention pond can be a wise investment in safeguarding your property against the devastating wildfires that often occur in Oregon. We’ve explored some of those reasons in the earlier articles in this series:
- We’ve discussed sharing the costs and use of a fire pond with your neighbors.
- We’ve taken a general look at paperwork and permitting.
- We’ve considered where the water will come from.
Now let’s talk about location, size, physical structure, and the infrastructure needed for an effective fire suppression pond.
Site Selection
When building a fire pond to protect your property or your community, the first consideration should be location. Consider how accessible the proposed pond will be to fire trucks and other firefighting vehicles and how pumping or extraction infrastructure will be installed.
Next, place the pond where maximum storage volume can be created, with minimal excavation, to optimize cost-effectiveness. Since excavation is typically the most expensive part of the project, minimizing it can help the budget. For example, if you can get approval from Oregon agencies, a site in a gully or swale is an excellent choice.
However, avoiding areas near dwellings, feedlots, corrals, drain fields, or any location that may produce contaminated runoff is essential. A contaminated pond can create algae, aquatic weeds, and heavy sediment, making it unsuitable for firefighting. It can also generate odor and health concerns for your family and neighbors.
Careful consideration of your pond’s location will ensure its maximum effectiveness in combating wildfires while minimizing costs and potential risks.
How Big is Big Enough?
The size of your fire pond should be determined by the size of your property and the potential fire risks. As a general guideline, a fire pond should be able to hold at least 10,000 gallons of water, the typical volume needed to suppress a single house fire.
The shape of the pond can be roughly circular or rectangular, depending on your preference and available space. When it comes to depth, it's recommended to have a minimum depth of 8 feet to ensure an adequate water supply.
Many people tend to associate pond size with surface area, but a deep pond will quickly outpace a shallow one for the volume it can hold in a limited area. Another factor to consider is that shallow ponds will lose more water to evaporation than deep ones.
Pond Structure
Typical fire ponds can be categorized into three main types: embankment, excavated, and combination ponds. An embankment pond is created by building a dam across a stream or watercourse in a ravine deep enough to contain at least five feet of water. The land slope can range from gentle to steep.
An excavated pond is dug out in a nearly level area, with the water capacity obtained entirely through excavation. Since the labor of excavating is so intense, excavated ponds are generally reserved for situations requiring a smaller water supply.
In other situations, ponds are built in areas with moderate slopes, and the capacity is achieved through a combination of excavation and embankments, where the excavated materials are used to construct the barrier, saving both time and money.
It’s vital to avoid placing an embankment pond where a dam failure could risk people or livestock, or damage buildings, roads, or ecologically sensitive areas. Safety should be a top priority, so consulting an engineer during design and construction is essential.
Fire Pond Firefighting Infrastructure
A fire pond’s primary purpose is to provide a dependable water supply for firefighting, and certain infrastructure elements are required so it can fulfill that purpose effectively. One or more dry hydrants should be installed so engines can quickly suction water from the pond and support firefighters in different parts of the property.
If the pond is located near houses or barns, having a centrifugal pump with a power unit and a hose that can reach all sides of the buildings is a good idea.
Although the water-storage requirements for fire protection are not extensive, the withdrawal rate for firefighting is high. Your local fire department can advise you on which fittings and sizes are compatible with their equipment and what flow rate they need.
To support multiple firefighting streams, you’ll need enough storage to operate all of them. One acre-foot of storage is sufficient for four streams, for example.
Embankment Safety: Spillways
A spillway is a crucial component of an embankment pond as it helps to divert excess water away from existing structures and inlets. During periods of intense rainfall, elevated peak discharges can threaten the pond’s integrity by exceeding the pond’s capacity and damaging outlet structures or embankments.
Designing the pipe inlet to accommodate such peak runoff is impractical, so an emergency overflow or spillway is essential, regardless of the pond’s size. The spillway routes water around or through the dam, preventing an overflow or breach.
Without a secondary water-drainage structure, the water level in the pond could rise to a point where it overtops the dam, causing damage to the downstream slope and potentially leading to the failure of the entire structure.
To ensure its effectiveness, the spillway should be located away from the dam’s center, where the natural topography intersects the excavation work. This placement protects the embankment from erosion and minimizes the visual impact on the pond.
