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Avra Valley Recharge Project

Introduction
Facility Components
Operations
Maintenance

INTRODUCTION

Avra Valley Recharge Project (AVRP) was Central Arizona Project's (CAP) first recharge project. It was first conceived as part of the Northwest Tucson Active Management Area (AMA) Replenishment Program, a cooperative effort of the local water entities that began in 1994. Located in the northwest portion of the Tucson AMA, the project consists of approximately 11 acres of recharge basins. CAP constructed and began operating AVRP in July 1996 as a 2-year pilot project and permitted the facility as a full-scale project in March 1998. The project is located near the Marana Airport west of the Tangerine Road exit off I-10. It was developed and constructed with State Demonstration Project funds.

Water is pumped from the CAP canal utilizing two natural gas-powered engines into an open channel irrigation canal. The water is diverted from the irrigation canal into a main distribution box. The facility is divided into four separate basins that range from 1.8 to 3.5 acres in size. The flow is measured using individual v-notch weirs at each basin.

Water delivered to Basin 3 at AVRP

Project Facts

Permit Capacity: 11,000 AF per year
Cost: $790,000
Basins: Four basins ranging from 1.8 to 3.5 acres
Total Acreage: 10.8 acres
Location: T12S,R11E, Section 3 SW Corner
Delivery Capacity: 12 cfs
Pilot Operation: 1996-98
Full Scale Startup; March 1998

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FACILITY COMPONENTS

AVRP consists of four basins ranging in size from 1.8 to 3.5 acres for a total of 10.8 acres. The water is delivered to the project using two natural gas-powered canal-side pumps that are capable of pumping up to 11,000 gallons per minute each (approximately 25 cubic feet per second). The water is pumped into an open irrigation supply canal and conveyed approximately 1 mile from the CAP canal before being diverted into the project by manually adjusting a slide gate in the canal.

Manual slide gate to divert water into recharge project

The water that is diverted into the basins enters a single concrete distribution box where it is delivered to the individual basins. At each basin, a separate concrete distribution box containing a v-notch weir measures the flow before entering the basin. The water level in the v-notch weir is measured using a pressure transducer inside a stilling well and recorded every 15 minutes. Also, pressure transducers are installed in each basin to measure change in the water levels to ensure the basins do not overfill.

V-notch weir with stilling wells at top of photograph

All the information collected at the project is recorded at a central SCADA system via remote data acquisition units powered by solar energy. The data is collected and transmitted by radio to the CAP Twin Peaks Pumping Plant where it is sent through the CAP microwave network back to the CAP Control Center.

Solar powered remote data acquisition system at AVRP

Lower Santa Cruz Recharge Project and AVRP are within the Federal Aviation Authority's (FAA) 10,000-foot radius of the Marana Northwest Regional Airport and, therefore, require mitigation to protect the airplanes from bird strikes. LSCRP, the larger of the two projects, employs the Phoenix Wailer that generates random noises to scare off loafing birds while at AVRP, passive bird mitigation is employed.

Passive bird mitigation at AVRP utilizing plastic-mounted owls

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OPERATIONS

AVRP began operations in June 1996 as CAP's first recharge project and consists of four basins totaling 10.8 acres. CAP entered into a Water Transportation Agreement with BKW Farms, Inc. (BKW) to wheel or transport water through BKW's agricultural irrigation canal system to the recharge basins. The flows are measured at the turnout of the CAP canal with a McCrometer propeller flow meter, and the flows that are diverted into the recharge basins are measured with v-notch weirs at the inlet to each basin.

With only 10.8 acres of basins, rotating basins is not practical, so when the project is operational, all the basins are receiving water. Infiltration rates vary from basin to basin. Basins 1 (SE), 2 (SW), and 3 (NE) average from 2.1 to 3.5 feet/day with Basin 4 (NW) averaging < 1 foot/day. A clay layer that impedes its infiltration rate underlies basin 4.

Water delivered to Basin 3

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MAINTENANCE

The maintenance schedule is dictated by observing the infiltration rates of the basins. With only 10.8 acres of basins, AVRP is operated at full capacity with no basin rotation possible. As the infiltration rates decrease, the methods used to rejuvenate the basins vary. When the infiltration rates first begin to degrade a single basin, drying is utilized to allow the fine-grained clogging material to dry and form desiccation (mud) cracks. Spring-tooth harrows are also used to break up the clogging layer. Finally, when the clogging layer becomes too thick, the basins are scraped to physically remove sediment using a 30-yard belly scraper.

Desiccation cracks formed on basin bottom from drying the clogging layer.

Ripping the basin bottom using the spring-toothed harrow.

CAP water does not carry a heavy sediment load. The fine-grained clogging material is primarily diatoms, blue-green algae, wind blown dust and unicellular green algae. The use of chemicals to control the algae is avoided to maintain the chemical quality of the recharged water.

Algae growth in the basins at AVRP

The control of weeds is important at AVRP due to the proximity of the Marana Northwest Regional Airport to reduce habitat for birds.

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