The natural basin of Navajo Lake includes three sink holes and highly fractured basalt at the east end of the lake that serve as the largest outlet source, allowing the lake to historically drain almost dry during drought years. In 1932, an earthen embankment was constructed across the entire lake basin to isolate the majority of the lake from the sink holes, establishing much more stable water levels and making it possible to maintain a sport fishery. Navajo Lake has since become an extremely popular recreational fishery (actually receiving more angler use during summer months than almost any other fishery in southern Utah) and is known for producing trophy splake (see attached reports in the "Images/Documents" section of this proposal). The fishery simply would not be able to exist without the embankment preventing the lake from going dry in drought years or getting low enough even in normal water years that hypoxia-related fish losses would be common every winter and spring. Unfortunately, the embankment has failed twice in recent years. The basin fills and inundates the dam on high water years over a relatively short period of time (almost entirely driven by snow runoff) with the water flowing over a spillway in the embankment, but the spillway is undersized and the water often flows over the top of the embankment, causing failure in 2009 and 2010. Additionally, the spillway is old and the concrete has deteriorated to where it no longer forms a chute, exposing the embankment to spillway flows more frequently. In order to maintain the fishery, the spillway and embankment need to function. This project would reconstruct the spillway and complete maintenance on the embankment to significantly reduce the future risk of failure.

The main goal of the project is to greatly reduce the risk of embankment failure and subsequent loss of the fishery by improving the spillway and embankment to better withstand up to 500-year flood events. Specific objectives would be to (1) completely rebuild the spillway about 1 foot lower and 10 feet wider with reinforced concrete and (2) complete maintenance work on the embankment (e.g., adding road base along the top of the embankment).

There is currently a high likelihood that the spillway will be insufficient to pass inflow from snowmelt runoff on any given year, greatly increasing the chances of a failure of the embankment. The repair of a major embankment failure could be cost prohibitive and would mean the loss of the fishery over the long-term.

The project meets general Utah Division of Wildlife Resources (UDWR) Goals and Objectives to maintain or expand fish populations and quality fishing opportunities. A public committee is currently working on a new Navajo Lake Fisheries Management Plan (NLFMP). The NLFMP is certain to include goals and objectives related to rebuilding the spillway and completing maintenance work on the embankment. A copy of the NLFMP will be uploaded to the "Images/Documents" section of this proposal as soon as it is finalized.

The project could help to maintain Navajo Lake as a source for water to fight fires in the area.

The project would help to ensure that Navajo Lake maintains at about 400-600 acres and does not go almost completely dry in drought years.

The project is essentially maintenance, limiting how much is required in terms of compliance. NEPA will not be required. All other possible permits/clearance (e.g., archaeological, ACOE 404) will be addressed/secured before construction begins.

The general plan and cost estimates are from a memo (attached in "Images/Documents" section of this proposal) from a professional engineer (PE) with the Utah Division of Water Resources outlining options for addressing the failing spillway and embankment at Navajo Lake. The Utah Department of Facilities, Construction, and Maintenance (DFCM) and an engineering company would oversee the vast majority of the project. UDWR personnel would assist DFCM and help supervise construction. The public bid process would be used to hire engineering and construction companies. The tentative plan would be to complete all plan/design/permit work by the end of summer 2022 and then complete construction work in the fall of 2022.

The new spillway and restored embankment would be inspected by the UDWR several times each year and maintenance completed as necessary. The fishery is monitored through gill net and angler surveys.

We are working closely with Utah Division of Water Resources, Dixie National Forest, Kane County, local businesses, anglers, and all other stakeholders.

The spillway and embankment would be inspected and maintained annually by the UDWR with assistance from the Dixie National Forest.

The fishery at Navajo Lake is maintained through sustainable levels of stocking and this project would not impact that management.

07/01/2022

06/30/2023

2023

The final methods did not deviate from the original plan in any meaningful way. The existing, severely deteriorated 20' Navajo Lake concrete spillway was widened to 30' and entirely rebuilt. Additionally, maintenance work was completed along the dirt and rock embankment of the dike (the embankment maintenance work was primarily to replace sections of the dike that had eroded and establish a consistent level, which would help with reducing future erosion). Material for the project was taken from on-site or nearby.

An engineering firm was hired in the summer of 2022 through a public bid process and finished the preliminary design for rebuilding the spillway and repairing the embankment. A contractor was then hired through the public bid process in the early fall of 2022 to complete the work to the specifications of the engineered designs. The Utah Department of Facilities, Construction, and Maintenance (DFCM) and the engineering company oversaw the vast majority of the project, with Utah Division of Wildlife Resources personnel assisting DFCM and helping to supervise construction. All work was completed by late fall of 2022. The old dike and spillway was only capable of passing a 10-year flow, while the new dike and spillway are now capable of passing up to 500-year flows. The new spillway and dike performed well in the early summer of 2023 when extremely high flows occurred from the melting of a historic snowpack.

The new spillway and restored embankment will be inspected by the UDWR several times each year and maintenance completed as needed. The fishery is monitored through annual gill net surveys and periodic angler surveys.