Pima County's Urban Oasis
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KERP Pima County’s Urban Oasis INTRODUCTION 31 e are standing on the edge of a vast basin Great Blue Heron , a Cooper’s Hawk and two swallows. W that’s nearly invisible from the surrounding streets. A 2.2-mile paved path for pedestri- This environmental restoration facility is the Ed Pastor ans and bicyclists hugs the perimeter and is often used Kino Environmental Restoration Project, or KERP for by office workers from nearby government buildings short. It is named for the Arizona congressman who as a place for lunch hour exercise. was instrumental in shepherding the project through Congress. It is a tranquil oasis A member of the Tucson where the practical and the Audubon Society looks into this aesthetic are perfectly blended. giant basin near Kino Parkway and Ajo Way and remarks on KERP is the end result of a the ponds and lush vegetation. multi-purpose environmental Willow, ash, cottonwood and restoration and stormwa- mesquite trees were planted in ter harvesting project. The what was once little more than a ponds are part of a carefully barren mud flat. designed flood control proj- ect that collects and captures The nearby office buildings rainwater from a 17-square belie the surrounding natural mile watershed that includes environment. It takes some ef- Davis-Monthan Air Force Base. fort to remember we are in the The harvested stormwater middle of the Sonoran Desert, is used to sustain the lush where 12 inches of rain in a wildlife habitat within KERP. 12-month period is considered a Extra stormwater irrigates Pima wet year. The Audubon member County’s Kino Sports Complex is looking through the trees at and surrounding landscaping, a Great Egret standing motion- providing a significant cost sav- less on the bank of the pond. ings to taxpayers. A moment later a flash of red darts across his field of vision, The lush habitat attracts a wide and an Anna’s Hummingbird variety of wildlife and wildlife Due to the high diversity of birds at KERP, it has become a popular settles lightly on a thin mesquite birding location watchers. More importantly, branch. KERP also protects down- stream homes and businesses. These areas would be In less than an hour of wandering the periphery of this devastated by flooding if stormwater were to follow its manmade flood control and environmental restora- natural path from the Eastside of Tucson to the Santa tion project, the birder points out two Night Herons, Cruz River. a Neotropic Cormorant, a Yellow-rumped Warbler, a 2 WATER IN THE DESERT f you stand today on the banks of the I Santa Cruz River near downtown Tucson or the Rillito Creek at Craycroft Road, you would be forgiven if you didn’t recognize that these now dry riverbeds used to provide year- round water for the lush forests and wildlife that once thrived there. Some 15,000 years ago, the physical environment of the region was markedly different than it is to- day. With the wetter and cooler climate during the last Ice Age, large mammals that have long been extinct – the Pleistocene bison, mammoth and The Santa Cruz River at the base of “A” Mountain near downtown Tucson camels, for example – could be found grazing in in 1904. grasslands and drinking from rivers and streams. Evidence of this history was found at the KERP site in 1990, when a County employee inspecting erosion cuts found a Pleistocene mammoth tusk buried in a prehistoric stream channel along the edge of the earthen basin. The reasons for the transition from lush aquatic ar- eas to the dry arroyos we see today are numerous, but the rapid increase in the human population beginning in the 1880s and the subsequent urban expansion and groundwater pumping are the main culprits for the more recent drying. Picture of the old arroyo just downstream from present-day KERP, 1961. By the year of Arizona’s statehood (1912), the Santa Cruz River near downtown was no longer flowing Summer rains come fast and hard; and desert year-round. soils are incapable of absorbing more than a small percentage of the rainfall. Rain that is not absorbed Nonetheless, intense rains – especially summer into the soil very quickly begins to flow laterally rains – turn the Santa Cruz River and other regional across the ground surface, gathering speed and waterways and washes into raging rivers that can force as it flows downhill. Urban development – overflow their banks and cause flooding. pavement in particular – aggravates the situation. 4 Less than 100 years ago, the area south deaths caused by the storm: “The Thun- of downtown Tucson was a broad derstorms with heavy rain overflowed the mesquite-lined wash surrounded by banks of an ordinarily dry wash and tore creosote desert that stretched largely a 15-foot gap in the bridge on Benson unbroken to the south, east and west of Highway. Four automobiles plunged into the city. the raging torrents where ten people were drowned while four others struggled out of As Davis-Monthan Air Force Base grew the floodwaters” and the city expanded to the east, rooftops and pavement covered larger expanses of Following this event, flood control became a priority the desert. Paved streets and runways offered less and in 1948 the area’s first major flood control proj- resistance to the rainwater that fell on the water- ect, the Tucson Diversion Channel, was authorized shed; and stormwater began flowing downhill more by the U.S. Congress. The long concrete and earthen rapidly. channel collects rainwater beginning near the northwest edge of the Air Force Base at Alvernon A storm on August 9, 1945 was ranked by the Na- Way and Golf Links Road. It crosses Tucson’s south tional Weather Service (NWS) as one of the top ten side, dumping floodwaters into the Santa Cruz River weather/climate events to impact Tucson in the last southwest of the Interstate 10/Interstate century. The NWS described the destruction and 19 interchange. 5 5 n 1999, Congress authorized construction bosque (bosque is a Spanish term meaning forest). I of the Tucson (Ajo) Detention Basin Environ- This riparian, or river-supported, area is surrounded by mental Restoration Project. The project’s nearly 100 acres of upland vegetation communities. purpose was threefold: 1) to preserve flood control function, 2) to harvest stormwater for irrigation, and 3) Several Pima County departments play a role in KERP to establish natural and riparian wildlife habitat. operations. Basin managers work closely with state and federal agencies to ensure KERP meets the state Construction of KERP began in 2000 and was complet- and federal guidelines set forth for water quality and ed in 2001 at a total cost of approximately $11 million. stormwater detention. The project was funded by the U.S. Army Corps of Engi- neers and Pima County. Local contributions toward the The District performs routine monitoring for mosqui- project totaled $6 toes and applies a million. bacterial larvicide Bti (Bacillus Thuringi- The final footprint ensis Israelensis) as of KERP covers 121 needed to protect acres and includes public safety. Re- constructed stream moval of non-native courses, five invasive plant and vegetation-lined animal species ponds, restored (i.e.: buffelgrass, native vegetation bullfrogs) helps to communities and conserve urban na- a recreational path tive species diversity. that surrounds the Pima County can basin. Aerial photograph of KERP looking south. purchase reclaimed water from the City of Tucson to supplement irriga- The project included installation of approximately tion needs of wetland vegetation during extended 850,000 square feet of rubberized liner under the drought. ponds and constructed stream courses. The project also includes a 6-acre, 50-foot-deep, cement-lined KERP won the 2006 U.S. Army Corps of Engineers Chief water harvesting basin. This basin collects and supplies of Engineers Award of Excellence for Environmen- the stormwater used for irrigation. tal projects. According to the Corps, “This is truly an exceptional project. It takes an existing mud flat in an arid The streams are fed by an elaborate stormwater area and creates aesthetic landscapes, recreation features, recirculation system, and these streams support over flood control, and is a prototype for water harvesting. It is 30 acres of open water ponds, emergent wetlands, technically sophisticated while appearing natural. It has ephemeral cienegas, stream courses and mesquite proved sustainable over the recent drought years.” 6 THE BENEFITS 7 he goal of the KERP was to establish an Water Harvesting Benefits T ecosystem in a flood control basin. How- Water harvesting is the collection of rain and sur- ever, the project also provides recreation- face water runoff. A sophisticated system of irriga- al and economic benefits. tion channels dating back to 1200 BCE was discov- ered on the site of Pima County’s Tres Rios Water Flood Control Benefits Reclamation Facility. The discovery of this site, with On September 15, 2011, 2.64 inches of at least eight canals and a series of rain were recorded at Davis-Monthan HARVESTED STORMWATER agricultural fields, is evidence that Air Force Base. More than 16,000 gal- ancient people in Southern Arizona lons per second of stormwater flowed Year Gallons manipulated water flow for their from the Tucson Diversion Channel 2002 39,099,480 benefit. into KERP. Because KERP is able to 2003 28,349,074 temporarily detain over 400 million 2004 10,003,639 KERP differs from most other water gallons (1,230 acre-feet) of stormwater, harvesting projects by capturing 2005 21,147,758 the outflow westward into the Tucson runoff from a stream channel, rather Diversion Channel was reduced by 2006 0* than directly from rooftops or open over a third to less than 10,250 gallons 2007 21,489,902 areas.