Ask the Contractor: Dry winter is a good time to plan rainwater harvesting
Updated as of Friday, February 16, 2018 1:20 PM
Have we time-warped into spring?
This extreme, “no-winter weather” condition is affecting our lakes and aquifers and our ski time. This crazy weather is having an effect locally on socioeconomic factors, too.
The lack of rainfall is having a significant impact on many aspects of our local economy and is greatly enhancing our quality of life; we are outdoors more this winter, hiking and “road tripping,” because of the glorious weather. And we are having a lot of wonderful visitors to our area.
But while many of us are out and about on these wonderful, warm and sunny days, ski resorts are missing the cold temperatures and seasonal snow.
Meanwhile, home construction and road construction is progressing at a more rapid pace with this temperate weather, instead of wet, cold snowy days.
Energy usage is closely linked with the weather, and the demand for energy — such as natural gas, propane and electricity — is less this winter.
Local businesses that rely on winter revenue are experiencing a decline in register sales; chain saws are not being used to cut winter timber.
Therefore, sharpening services are down.
From a picturesque point of view, our beautiful Arizona wildflowers will certainly be affected by the lack of moisture this winter. On the plus side, however, spring flowers are already popping.
The lack of winter moisture will certainly increase the threat of wildfires, and the warm winter will likely enhance proliferation of forest and woodland insects.
While you might think this unusually dry and warm winter is a crazy time to talk about rainwater harvesting, I had four calls over the past week from homeowners who wanted to know about rainwater harvesting.
Residential rainwater-harvesting methods vary from simple earthworks, designed to divert and catch surface runoff, to complex systems that collect water from roofs and other surfaces, direct it to storage tanks and pump the water to its destination.
To begin rainwater harvesting, you must consider seasonal rainfall patterns, topography of your property, roof catchment area, water requirements of your landscape or garden, water storage (in soil or tanks), and, of, course your budget.
Passive rainfall harvesting systems rely on manipulation of topography and smart design. Earthworks — such as berms or swales — can be constructed from soil to create areas where water is diverted and/or collected for direct infiltration. On flat ground, you could create lower-elevation basins -- often called rain gardens -- to collect harvested water. On a slope, berms should be crescent-shaped, higher in the center than the edges, and formed where they will catch surface runoff coming down the slope.
If you are considering paving an area, you may want to use pervious pavement, to allow infiltration into the ground of some water, while directing excess water to basins. Permeable pavements allow water to infiltrate through or in between the paving material. Paving materials such as brick or concrete pavers and flagstone can also be set in sand, rather than concrete, to allow water to enter the soil if desired. There are also pervious concrete mixes that contain coarse aggregate and little or no sand.
The potential volume of water available for harvest can be estimated by knowing the relationship between inches of rainfall and volume of water: one inch of rainfall equates to 0.62 gallons per square foot of horizontal surface area. For instance, given the average city lot (1/4 acre or 10,890 sq. ft.) and average rainfall -- let’s use 12 inches/year -- this calculation yields 81,021 gallons of water (7.48 gal./cubic ft.).
In reality, it is impractical to try to capture or redirect all this water for use by plants or people, but that can be a goal. Calculating total amounts provides some idea of the volume of water moving through your landscape on a yearly basis.
Household water-harvesting systems commonly utilize the roof of the home and other buildings as a collection surface. You can collect 600 gallons of water per inch of rain from 1,000 square feet of catchment surface, in which the water is collected via rain gutters, downspouts and collection pipes and diverted into a storage container.
The simplest and least expensive storage containers are plastic barrels. Two or more containers can be connected with PVC pipe that allows water to flow from one barrel to the next. Steps should also be taken to seal the barrel, to limit access to mosquitoes and small animals that could fall in and drown. There are also specially designed downspout filters and other accessories to improve water quality and harvesting efficiency.
More complex water-harvesting systems utilize larger storage tanks to store harvested water and pumps to distribute it when needed. The tank can be above or below ground. You can use commercially purchased water tanks or home-built tanks, constructed from a corrugated-steel culvert, set upright in concrete. The advantage to the above-ground cistern is that gravity can be used to direct water to areas where irrigation is needed.
While I am not even thinking of turning Yavapai County Contractors’ Association into an organization to scientifically study the earth’s atmosphere and weather patterns, I found it interesting, anyhow, in looking at the National Climatic Data Center web site that “based on the Palmer Drought Index,” this area is experiencing a severe/moderate drought condition. And the precipitation required to end our current drought in 1 month would be 7.6 inches of rain. The drought outlook for the rest of February and into March is going to persist, and the Palmer Drought Severity Index has our area currently at -3.33.
While Arizona is reported to be in a severe drought condition, and, as a result, we have issues of wildfire and insects looming, we must take an active role in water conservation and do our part to be water smart. So let’s harvest the rainwater we receive or, at least, get ready to harvest rainwater whenever it arrives.
Sandy Griffis is executive director of the Yavapai County Contractors Association. Email questions to her at firstname.lastname@example.org or call 928-778-0040.