Existing diversions structures and acequias of the lower Rio Chama
Using aerial imagery, 12 diversion structures were identified on the lower Rio Chama: nine rock structures and three concrete structures. The diversions are an impedance to the natural flow and function of the river and are vulnerable to damage from high flows, the rock diversions especially. Nevertheless, the diversions serve a very important role in irrigation and cannot be removed completely but there would be benefits to fewer diversion structures in the river.
Multiple irrigators who share a diversion would share the financial and labor burden of regular maintenance and repair any damage that may occur
Fewer backwater areas where increased sediment deposition occurs and poses a flood risk; better sediment flow overall
If maintenance and repair burden is lessened, irrigators may be more likely to keep their traditional rock structures than to replace them with a more durable concrete structure is given the opportunity to do so
Fewer structures would improve fish passage
Fewer structures would reduce obstacles to boating that inhibit development of recreation opportunities
Consolidated diversion structures must be able to handle a greater quantity of water than the existing individual structures do because it must serve multiple acequia headgates. Removal of a structure would lead to the remaining structure(s) being reinforced or reconstructed to effectively serve all of its acequias and to better withstand high flows. The materials for strengthening the diversion structures to be considered are concrete weir, rock grouting, sheet pile, and gabion boxes.
ALTERNATIVES FOR STRENGTHENING CONSOLIDATED STRUCTURES
The 12 diversions were analyzed to identify if there is an area where closely spaced diversions could be consolidated. One such location was identified and named the focus area. The focus area has three diversions (labeled as 7, 8, and 9) which service four acequias. It was determined that, if the diversions at this site were consolidated, diversion 7 could be removed and diversion 8 strengthened so that it can efficiently serve its acequias. The two acequias on the southern side of the focus area would benefit from realignment to move their headgate closer to diversion 8. This focus area was used when considering what reinforcement or replacement methods would be effective on the lower Rio Chama.
FISH PASSAGE
Fishes cannot directly pass through this diversion structure so fish passage system needs to be constructed separately along the diversion structure. The design objective for resilient ecology is maintaining a habitable environment for vegetation and fish species. Department of Fish and Game has led initiatives to maintain fish habitat. Fishing in the lower Chama is an economic driver in the region. Fish species are introduced for the fishing seasons. There are limits in which native and non-native species can be fished out. When diversion structures are consolidated, there is a chance that it might disrupt the migration for fish. To address this issue, fish ladders can be constructed along the diversion structures. Fish ladder’s design depends on the jumping height of the fish species.Fish passage must be constructed in conjunction with the diversion structure. Fish passage can be made with the same material used for diversion in cases of concrete diversion and rock dam with grouting. For gabion and sheet pile dams, fish passage much be made with a different material. Fish ladders can be made using concrete or steel. The major advantage of having a fish ladder is that fish can easily migrate for seasonal change or breeding pattern. Fish ladder will aid in maintain the fish ecology of the region.
AUTOMATED HEAD-GATES
A concern for irrigators in the area is when high flows occur and they are unable to open their headgates in time to alleviate the pressure applied by the flow. An automated headgate is a potential solution to this issue. Automated headgates can be calibrated so that when flows of a certain magnitude occur, the gate can open immediately. Several commercially available automated headgates exist (examples can be found here and here) and many are solar powered so they can be utilized in areas where electricity is less readily available. Actuators that can be fitted to existing gates (if the existing gate is suitable) are also commercially available. An example of a commercially available actuator can be found here.
Example of automated slide gates. (Rubicon, 2017)
PERMITS
Permits are required if there are plans to construct in a river. EPA would require permits for construction related to consolidating structures. Section 404 Permit Program Section 404 of the Clean Water Act (CWA) establishes a program to regulate the discharge of dredged or fill material into waters of the United States, including wetlands. Activities in waters of the United States regulated under this program include fill for development, water resource projects (such as dams and levees), infrastructure development (such as highways and airports) and mining projects. Section 404 requires a permit before dredged or fill material may be discharged into waters of the United States, unless the activity is exempt from Section 404 regulation (e.g., certain farming and forestry activities). Compensatory Mitigation This page provides updates and background information regarding Clean Water Act Section 404 Compensatory Mitigation Requirements. In 2008, EPA and the U.S. Army Corps of Engineers jointly promulgated regulations revising and clarifying requirements regarding compensatory mitigation. According to these regulations, compensatory mitigation means the restoration (re-establishment or rehabilitation), establishment (creation), enhancement, and/or in certain circumstances preservation of wetlands, streams and other aquatic resources for the purposes of offsetting unavoidable adverse impacts which remain after all appropriate and practicable avoidance and minimization has been achieved. National Environmental Policy Act (NEPA) NEPA Handbook from Bureau of Reclamation (Reclamation) on Managing Water in the West might also be involved in the permitting of using equipment in the river.
References
Rubicon. (2017). SlipGate®. Retrieved from https://www.rubiconwater.com/modules/prodcatalogue/files/28603/719/719_Rubicon%20Data%20Sheet%20SlipGate%20%28English%20US%29.pdf