Native Aquatic Species of the Gila River Basin
in Arizona and New Mexico
Aravaipa Creek Fish Barriers - Design Criteria
Design Considerations
The fish barriers were engineered and designed at Reclamation's Phoenix Area Office (PXAO) by the Engineering Division. The reinforced concrete pile design was reviewed with assistance of Reclamation's Technical Service Center (TSC), located in Denver, Colorado.
Initial investigations for a construction site within the Aravaipa Canyon Wilderness Area were determined to be infeasible. Private land downstream of the wilderness area was considered, but landowners were opposed to construction of the fish barrier project. As a secondary option, a site on San Carlos Apache allotted land downstream of the private property boundary was selected.
Specific design criteria guidelines for construction of the fish barrier structures were established by the U.S. Fish and Wildlife Service, as follows:
1. Construct the barriers to prevent upstream fish movement during a 100-year flood.
2. Construct two distinct barriers for multiple protection and to create a management area.
3. Construct the barriers with a minimum 4-foot vertical drop.
4. Construct apron downstream of the drop to prevent the development of a deep scour hole.
Designing the barrier structures proved to be a difficult and challenging task, with the barriers constructed on alluvium foundation material and anchored only to bedrock at the abutments. The difficulty was designing a stable structure that could resist scour, sliding, and overturning forces produced during the occurrence of large flooding events.
The fish barrier structures were constructed of reinforced structural concrete with the following components; upstream and downstream cutoff walls below grade, support piles beneath the barrier aprons, apron slabs on grade, and 4-foot vertical drop crest walls above grade. The barrier structures were secured to the abutments, by anchor bars embedded into keyway slots chipped into the abutment bedrock. Rip rap material was placed downstream of the barrier structures within the high velocity portion of the stream channel, as erosion protection and to reduce scouring.
The purpose for the upstream and downstream cutoff walls was to prevent scour damage and undermining of the barrier structures. The upstream and downstream cutoff walls were 3-foot thick, and varied in height form 8 feet to 16 feet dependent on their locations within the stream channel. Scour depth calculations indicated scour depths up to 16 feet in the high velocity zones below the channels, and scour depths up to 8 feet in lower velocity flows at the abutments.
The design incorporated reinforced concrete piles as additional support beneath the structures, in the event anticipated scour depths were exceeded and to provide sliding resistance for the structures. A total of ten 4-foot diameter piles with reinforcement steel in the upper 30-foot were constructed, 6 each for the downstream barrier and 4 each for the upstream barrier. A 60-foot depth was specified for all piles placed on alluvium foundation material. The pile depth was shortened accordingly for piles founded on bedrock, with piles placed on alluvium foundation material. The pile depth was shortened accordingly for piles founded on bedrock, with piles socketed into bedrock approximately 3 feet.
The concrete apron slabs downstream of the 4-foot barrier drops, were specified to prevent a deep scour hole from developing downstream of the structure. In addition, the apron slabs created a shallow high velocity flow condition downstream of the barrier drop, which further reduces the potential for fish passage. The apron slabs were 2.25 foot thick, and varied in length from 25 feet at low velocity flows near the abutments to 35 feet at higher velocity zones in the vicinity of the existing stream channel.
The 4-foot vertical drop crest walls are the principle component in controlling fish migration upstream. The barrier structures followed the original ground contour across the entire channel for the most part. The top finished grade of the crest wall drops was approximately 4-foot higher in elevation than the existing ground surface, except for notches designed into the barriers at the existing stream flow locations. Notches were designed and sized to promote sediment transport over the barriers to minimize stream migration, and to maintain the course of the original stream flow channel.
Excerpt from Technical Report of Construction, Aravaipa Creek Fish Barriers,
San Carlos Apache Allotted Land, Central Arizona Project dated June 2003.
ARAVAIPA DESIGN SUMMARY AND OPERATING CRITERIA - (.PDF Approx 34KB)
Last Reviewed:
August 10, 2007