Water Resource Design
Elements of Place
A fundamental of regenerative design is that there is to be a dialogue between the things we make and the place in which they take root. For buildings, this means allowing the resource richness or scarcity of a particular location to inform the design process and to be evident in the final result. Sunlight, fresh air, and water resources are essential aspects of the natural environment that can, and should, inform each place that we regenerate.
A building informed by sun and air is recognizable. It is well daylit year-round, its windows are open in the shoulder seasons, and it wears a crown of thoughtfully organized solar panels. The same can be said for a built environment that is informed by the ecological flow of water, though a more subtle reading of the solution is required.
Winter snow accents parapets and ledges. Ice builds on rain-chains during freeze-thaw cycles. Plants that are familiar regenerate in the thawing of Spring. Snowmelt mixes with rain and is conspicuously stored, offering resilience through the heat of the coming season. Late Summer thunderstorms become a celebration as cisterns overflow, filling swales and recharging the earth. Leaves are shed in the Fall, finding their way to the bottoms of swales. Grasses are bent and crushed under early snows. Water slows. Ice forms. The process repeats – but a little differently each year.
Process Fundamentals
The starting point for designing an ecological water flow is precipitation. While annual precipitation totals are important, it is seasonal variation that drives strategy. A place that has a fairly consistent precipitation pattern has an enormous advantage over one that has a discernable wet and dry season since storage needs increase with the length of that dry season.
For our Watershed Row project in Klamath Falls, Oregon, irrigation demand is expected to outpace supply during the drier Summer months, drawing down a 17,000-gallon cistern to 12% of capacity before being replenished in the wetter Fall months. A larger cistern or a non-potable backup source is needed in order to provide climate-change resilience.
If Watershed Row were to be relocated to Park City, Utah, without changing the outputs demand would only be expected to outpace supply one moth of the year. The conclusion is that a smaller cistern could do the job in Park City’s climate (storage limited to 2,500 gallons in Utah).
Once the source is understood, possible uses can be considered. Will the stored water be used for outdoor irrigation? Indoor irrigation? Toilet flushing? Another relevant non-potable use? Are there complimentary seasonal use patterns between contemplated uses that can be leveraged? Planting areas, evapotranspiration rates, fixture flow rates, and occupancy schedules need to be estimated so that water use volumes can be calculated and compared.
Ultimately, storage volume is a function of a location’s precipitation rate applied to a design’s discrete collection area. Collection surfaces such as rooftops and canopies can gravity-feed into above or below ground storage tanks. Rain and snowmelt aggregated from non-ground sources are generally suitable for non-potable uses such as irrigation and toilet flushing. By organizing the components of the collection and storage system vertically, pumping energy can be minimized or avoided.
By comparing monthly storage volume potential to expected monthly water demand for the envisioned uses, a balance point can be calculated. Contingencies related to climate-change must be applied so that storage tanks are less likely to run dry during times of drought. Similarly, overflow pathways need to be considered for each element of the system so that ecological flows are reinforced when cisterns are already full and precipitation is abundant.
Precipitation Collection Model
Place Collaborative has created an open-source Precipitation Collection Model in spreadsheet form that demonstrates how location and design interact in pursuit of place-based water use reduction strategies. By using the tool iteratively, an intuition regarding suitable solutions for a given place will form over time. Consult and collaborate with accredited and licensed professionals in order to determine the suitability of inputs and outputs before deploying contemplated strategies.
