Rock Creek Reservoir: Feasibility Study and Preliminary Dam Design

Project Overview

Cache Water District (CWD) is searching for several smaller dam locations at high elevations as potential solutions to future water shortages. CWD requested Boucher Engineering perform a feasibility study for a dam in the Blacksmith Fork River watershed.

The proposed reservoir project must:

  • Provide 5,000 to 10,000 acre-ft storage capacity.
  • Be located in a watershed that has the capacity to consistently fill the reservoir.
  • Provide new recreational opportunities.
  • Maintain flow in the Blacksmith Fork River during peak demand.

Alternative Analysis

Boucher Engineering conducted an alternative analysis to determine the most effective alternative for the achievement of the goals set forth by CWD.

Table 1 – Design Alternatives and Assessment Criteria

Design of Chosen Alternative

Stage Storage: The existing topography represents the bathymetry of the proposed reservoir to relate reservoir elevation to reservoir storage (see Figure 1).

Safe Yield: Boucher Engineering built a numerical model using existing data from the Blacksmith Fork River. The model estimates reservoir level, storage (see Figure 1), and demand and spillway releases over time.

Dam Stability: Calculations were done to determine if the dam would overturn or slide; The dam has a factor of safety (FOS) of 1.52 (see Figure 2).

Outlet Works: The bottom outlet works were designed to sustain conservation flows. The auxiliary spillway design is an 8 ft ogee crest weir that is capable of passing the design storm (see Figure 2).

Figure 1 – Stage storage and safe yield storage relationships.

Conclusions

Boucher Engineering determined the preferred alternative is an RCC Dam in the Rock Creek Canyon.

  • Proposed reservoir total storage: 6,327 acre-ft
  • Potential for public recreational areas on reservoir and adjacent areas.
  • Safe yield indicates the Rock Creek watershed can support filling the reservoir while maintaining conservation flows.
  • Outlet works successfully attenuate design storm flows and mitigate flooding downstream.
Figure 2 – Proposed plan and cross section of Rock Creek Dam.
Figure 3 – Proposed location for Rock Creek Reservoir.

Acknowledgements

Dr. John Rice (Utah State University), Greg Richards (Gannett Fleming), Dr. James Evans (Utah State University), Dr. Bethany Neilson (Utah State University), Austin Ball (Utah State University), Nathan Daugs (Cache Water District), Dr. Jim Bay (Utah State University)