Drought: Five Things You Need To Know About This Rainy Winter

By Warren Tenney

Many people are wondering what this rainy, snowy winter means for Arizona after more than two decades of drought. Here are five things we know right now.

1. It’s raining and snowing in the right places. So far, it has been raining and snowing in locations that have the potential to increase water in two major reservoirs, Roosevelt Lake and Lake Mead. These reservoirs are key to drinking water supplies for the majority of Arizona’s population.

  • Lake Mead relies on runoff from snow pack in the Upper Colorado River Basin, primarily from two main tributaries: the Green River in southwestern Wyoming and the Upper Colorado River in western Colorado. December snowpack in the Colorado River Basin has ranged from 50 percent to three times above normal.  The result of this above normal precipitation will likely boost the reservoir levels of Lake Mead.
  • Roosevelt Lake relies on rain and snow in the watershed that feeds the Salt River. This watershed reaches into the high country northeast of Phoenix. So far, the watershed has received about 45 percent more precipitation than normal. As of January 25th, 211,000 acre-feet of water had flowed into Roosevelt Lake. (One acre-foot of water is enough to serve three average Arizona households for a year.)

2. This is a good start. Weather in February and March must remain cold and wet to hold and increase the gains and potential gains in both reservoirs. Water resource managers are pleased with rain but prefer snow accompanied by extended weeks of cold temperatures. Low temperatures keep the snow on the ground longer, which stops the water in the ground from evaporating and helps to reduce the threat of summer wildfires. The slow flow from melting snow also delivers cleaner water and is easier to manage in a water delivery system. So while it has already been a good winter, we will have to wait until April to know if it has been a great season.

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This is a map of the  watershed where the springs, creeks and rivers originate that feed into Roosevelt Lake, a key drinking water reservoir for the Phoenix Metro area.

3. The drought is not over. Research shows that drought cycles and wet cycles in Arizona run 20 to 30 years. A drought cycle has fewer wet years than dry and a wet cycle has a greater number of above average rainy years. The current record-breaking drought cycle began around 1996. The last six years have been the driest on record in the Salt and Verde rivers’ watersheds. If the weather follows historical trends, the current drought could be coming to a close within the next several years, but there’s no certainty and it does not factor in climate change. It would take a few years of greater than average snow and rain to begin to heal the wounds left by the current drought. This includes helping to replenish local aquifers used to back up water available in dams and reservoirs. Plus, two or three years of well above-average precipitation on the watersheds that feed the Salt and Verde rivers would help to re-establish depleted wildlife, such as quail and deer. That much precipitation would help to restore overgrazed grasslands and begin to create a healthier forest, with trees not as susceptible to diseases and bark beetle infestation.

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4. AMWUA cities are built for drought. Sunshine is the norm in Central Arizona and rain is an event. We have never denied that we live in an arid part of the country and we plan for drought cycles. AMWUA cities save water underground for future use, keep leaks within their water distribution systems to some of the lowest rates in the country, and re-use 99 percent of their wastewater. Salt River Project (SRP) operates the system of reservoirs and canals that store water from the Salt and Verde rivers. After a rare rainy year in 2010, SRP has faced six dry years on the rivers’ watersheds. Despite record low precipitation, Roosevelt Lake has remained half full and SRP has been able to fill water orders for farmers, industries and cities. SRP was forced to limit water orders by 33 percent in 2002, the driest year in the Southwest in 1,200 years. That year, the SRP system was only 25 percent full and Roosevelt Lake alone was down to 10 percent full. It was the first reduction since the 1950s.

Central Arizona Project (CAP) operates the canal that brings Colorado River water released from Lake Mead to Arizona. CAP has not yet had to reduce water supplies due to a Colorado River shortage. The state’s cities, farmers and industries currently are working together to maintain and increase the level of water stored in Lake Mead and prevent a water shortage declaration next year. The recent increase in winter precipitation and snowpack in the Colorado River Basin decreases the chances that a shortage would be declared in 2018. So, while we regularly face metrological droughts, our water supply droughts are rare.

5. You can make the rain count. Homeowners, apartment managers and businesses make a contribution to our reservoirs when they turn off their irrigation systems and auto-fills on their pools each time it rains. More homeowners and communities also are harvesting the rain by contouring their landscapes to hold storm runoff. Swales built around trees and plants help rainwater stay in place longer so the water soaks deep into the landscape and stays available to plants and trees longer. All of this reduces the need to irrigate and the demand on city water supplies, which in turn saves more drinking water for drinking.

For 48 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit http://www.amwua.org. 

 

Putting Storm Runoff To Work

By Warren Tenney

Cities in the Phoenix Metropolitan area are experimenting with building methods to slow storm runoff and allow more of it to be absorbed into the ground instead of rushing into streets and down storm drains. Low Impact Development (LID) is an approach to land development – or redevelopment – that mimics the natural environment by encouraging rainwater to stay in place and to sink into landscaping and planters, soak through sidewalks and parking lots made of permeable pavement, pour off roofs into cisterns and rain barrels, even collect on rooftop gardens. LID practices aim to preserve, restore and create green spaces using soils, vegetation, and rainwater harvesting. The City of Tempe has just taken a big step forward in determining how to make LID work for desert cities.

Cities are taking a hard look at Low Impact Development methods for building streets, commercial developments and planned residential communities. The methods could reduce water used to irrigate landscaping, prevent street flooding, and allow cities to downsize expensive storm drain systems. For example, the City of Phoenix maintains an 895-mile underground storm drain system. During the Valley’s infrequent but often hard and fast rainstorms, runoff rushes into 18,641 catch basins cut out of Phoenix sidewalks and along streets or into grated dry wells often located in parking lots. Many of the storm drains eventually empty into the Salt Riverbed.

Last year, the cities of Mesa and Glendale, working with the consulting firm Logan Simpson, created the Low impact Development Toolkit, which offers technical variations of techniques that make the most out of storm runoff. Mesa and Glendale have used Low Impact Development techniques on several public projects and plan more. For example, Mesa used curb cuts that allow runoff to collect in shallow basins and irrigate street landscaping around Fiesta Mall, along Southern Avenue at Alma School Road. Glendale used permeable pavement in a 6-acre park-and-ride lot at 99th and Glendale avenues where water sinks through the pavement and into the ground.  

Now, Tempe is adding another piece of critical information about Low Impact Development in desert cities. Tempe, working with the Flood Control District of Maricopa County and contractor J2 Engineering & Environmental Design, used new technology to create a model that divided most of the city into 20-square-feet grids. New highly detailed topographical maps allow engineers to know how much grass, pavement and gravel are contained in each grid and if there are buildings or fences or walls. Then consulting engineers used computer-modeling techniques to determine what happened to runoff in each grid during the lightest to the heaviest rainstorms. Linking the grids has given the city the most accurate storm runoff data available. (These computer-modeling methods have been around for many years, but only within the last 5 years have typical computers been powerful enough to model entire cities.)

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Tempe neighborhood as it is now.

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Model of Tempe neighborhood with LID techniques.

Here’s the interesting part: Tempe and its consultant modeled a small portion of a neighborhood with a history of flooding problems by dividing it into even smaller 4-square-feet grids. The city then overlaid the model with different Low Impact Development techniques. This model produced the state’s most detailed and quantifiable data about the effect of Low Impact Development techniques on storm runoff. The small section of the neighborhood was modeled using different Low Impact Development methods, such as driveways made of permeable pavement and yards contoured to hold water and release excess water into permeable underground pipes. The model included street landscaping created with curb cuts and swales to hold stormwater and even a roof garden on a nearby school building. Runoff was measured using different combinations of Low Impact Development techniques and different percentages of homeowners using the techniques.

Here’s what the City of Tempe found out: If 50-75 percent of homeowners agreed to participate and applied the suggested Low Impact Development techniques to their property, flooding would be mitigated enough to downsize a proposed new storm drain system for the area. The city has concluded that retrofitting established neighborhoods with Low Impact Development techniques is possible and worthwhile. 

Making it work, however, would require a partnership between homeowners and the city and that needs more research. What is the best approach to engage and assist residents to apply Low Impact Development techniques to their yards?  What tools and information will they need?  Would rebates be an effective means to encourage homeowners to invest in revamping their landscapes and driveways, similar to turf removal incentives? 

For now, these Low Impact Development techniques would be most practical when used on public property, such as parks, streets and sidewalks, and when they are built into large new residential or commercial developments or redevelopments.

Quantifying the effect of Low Impact Development is a big step toward helping it to gain traction in desert cities.  Cities will be able to demonstrate the value of integrating these techniques into the community to better manage stormwater, reduce infrastructure costs, potentially offset landscape irrigation, and to enhance our built environment.

For 47 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.