Dibble provided topographic survey, drainage design, and plan preparation for dam repairs to Little Hell's Canyon Dam. The project was located in a steep area prone to scour. The new spillway outlet was designed to mitigate scour while protecting the dam embankment including a 96 foot wide concrete channel.
Lake Havasu City's system of washes are unprotected channels that regularly experience erosion, scour, sedimentation and head-cutting from storm events. Some wash beds have been eroded over time, and banks have scoured such that roads, structures and some utilities appear to be at risk. Dibble has evaluated the physical conditions, hydraulics and proximity to nearby roads and structures of all 77 miles of washes based on their risk of failure. This has resulted in a criticality ranking of each wash reach for master planning cost effective improvements, and meeting the budgetary constraints of the City. Dibble is designing a unique system of cost effective modular structures that the City can build, which will stabilize the wash beds and re-establish their original elevations over time. Dibble is also leading the City's effort to obtain a Regional General Permit from the US Army Corps of Engineers. This unique permitting method allows the City to make improvements to the washes, limiting applications for separate permit applications each time.
A joint project between the Airport and Dibble solved a long-standing safety problem at Chandler Municipal Airport. An existing retention basin at the end of Runway 22L/4R drained so poorly that Airport staff had to pump stormwater out of the basin after each rain event, which usually lasted many days and attracted waterfowl, a significant threat to aircraft using the runway. After evaluating alternatives, Dibble designed a solution which connected the retention basin to an adjacent offsite retention basin/park. The Airport's basin was also re-graded and drywells were installed in both basins to ensure that the entire system emptied within FAA requirement of 36 hours.
Dibble provided design and construction of the Lower El Mirage Wash Basin and transformed 24-acres of a rough-graded eyesore into a showcase park that is now the pride of area residents. From the beginning of the design phase, the Flood Control District of Maricopa County and the City of El Mirage approached the project in the spirit of partnership. As a result, Dibble Engineering and Environmental Planning Group were able to produce a truly integrated design that served both the District in its regional flood hazard mitigation activities, as well as the community of El Mirage in providing a safe community recreation space. This project received the 2014 Arizona APWA Project of the Year in Structures.
Dibble provided design and post-design services for two miles of 6-lane freeway, including two traffic interchanges at Bethany Home and Glendale Avenue with full access ramps. Design scope also included traffic signals, lighting, drainage, signing and marking, utilities, geotechnical engineering, traffic control, sound walls, and landscaping. Significant drainage design involved more than 85 inlets with collection lines and outlet to the regional flood control channel for the 10-year storm event. An offsite regional flood control concrete channel was designed to pass the 100-year, 24-hour existing condition flows with no freeboard and future conditions with freeboard. The channel design included varying channel drops as needed to optimize cost and effectiveness.
Dibble developed pre-design features for regional drainage improvements to the Watson Drainage System as identified in the Buckeye Area Drainage Master Plan. The pre-design refined and firmly established the project alignment and features, determined design constraints, resolved unknowns, and clearly established the final design criteria. The proposed system features include open channels, regional retention basins, and reaches of underground storm drain. Five different channel types, employing, five different lining materials were used for this system. Channel velocities were evaluated to ensure the stability of the proposed channel banks.
Dibble completed the design and construction management for major offsite infrastructure for an approximate 106 acre mixed use development, which included significant regional and local drainage elements. The project included design of approximately 1-mile of Dove Valley Road, an urban arterial roadway with several off-site flow crossings. These include a low-flow culvert with high-flow dip crossing of Skunk Creek, a regional wash with an upstream drainage area of approximately 50 square miles. The Skunk Creek crossing included scour and sediment transport analysis, compliance with EPA 404 and 401 federal regulations, as well as FEMA floodplain revisions meeting the requirements for a Letter of Map Revision. On-site drainage elements included underground storm drain, retention, and channels meeting City of Phoenix requirements for major collector roadways and commercial site development. This project was completed under an aggressive schedule.
This project consisted of evaluating alternatives for drainage improvements to the West Retention Basin at Chandler Municipal Airport. The West Retention Basin is currently located within the Runway 4L RPZ and is a major wildlife attractant and poses a serious risk to pilots taking off and landing on Runway 4L.