US Army Corps of Engineers
Los Angeles District

Alamo Dam Water Control Plan

Published May 3, 2018

LINKS:

Water Control Plan Update Scoping Session Posters


Overview of the Proposed Water Control Plan Update

Alamo Dam’s current 2003 Water Control Manual contains a Water Control Plan and an Environmental Impact Statement (EIS) and Biological Opinion (BIOP) developed in 1999.  The Water Control Manual is the Corps guiding document on how the project holds and releases water from Alamo Reservoir to meet its congressionally authorized purposes. To fix or clarify certain issues as well as address changed circumstances the Corps intends to re-evaluate existing operations at Alamo Dam to determine if changes to the Water Control Plan – and thus changes to how Alamo Dam is operated - are warranted.

The Corps is currently conducting scoping for the proposed reevaluation of the Water Control Plan.  During this initial scoping phase the Corps is soliciting comments from all interested parties: the public, Federal, state, and local agencies and officials, American Indian tribes, and others for consideration during the evaluation phase. Scoping is conducted after the agency determines there is a need and purpose for an action but before the agency begins drafting the NEPA document.  The intent of Public Scoping is to identify subjects of concern to review in the environmental impact statement (EIS) and produce a list of key factors to be analyzed in the EIS developed for the Water Control Plan. 

After public scoping is completed the Corps will develop the draft EIS.  Once the draft EIS is completed, it will be released for public comment and review.  After the draft EIS comment period closes the Corps will review and respond to all received comments in an appendix to the final EIS or if comments are received that bring to light new or previously unknown information requiring substantive changes to the draft EIS, the draft EIS will go out for public review again after the changes are made. 

If you are unable to attend a scoping meeting, and would like to submit comments on the proposed Water Control Plan update please submit your comments via email to AlamoDamSPL@usace.army.mil, using the subject line “Water Control Plan Update Scoping Comment”.

Why update the Water Control Plan?

Under existing operations, Alamo Dam has several ongoing issues:

  • Since 1999, several new species have been protected by the Endangered Species Act and new critical habitat has been designated that may be impacted by project operations.

  • Because flushing release flows from the dam aren’t routinely made sediment builds up and becomes anoxic, generating corrosive and hazardous hydrogen sulfide gas.

  • The existing bulkhead gate was not designed to operate at the higher water surface elevations the project is now managed for making the performance of routine maintenance problematic. The design and means of using the bulkhead gate need to be reviewed.

  • Certain portions of the Water Control Plan may be difficult to implement due to limitations of the project’s aging hardware.

  • Based on preliminary information, the largest design flood [theoretical] used to assess the dam’s performance in an extreme event would cause the dam to be overtopped using the current water control plan.

  •  Current project maintenance requirements are difficult for the Corps to implement due to the need to complete required compliance efforts associated with a newly listed species and newly designated critical habitat under the Endangered Species Act [ESA].

  • In 2002, the Corps included Alamo Dam in the initial set of projects involved in the Sustainable Rivers Program, a joint initiative with The Nature Conservancy.  This will provide the Corps with another perspective when considering various alternatives for operating the project.

What type of changes might be made to the Water Control Plan?

1. Adjust the target lake elevation:

            a) Increase target lake elevation

            b) Decrease target lake elevation

            c) Leave target lake elevation the same

2. Modify the reservoir release pattern:

            a) Shape releases to mimic natural flow patterns - high flow events during rainy season

            b) Maintain existing release pattern

            c) Higher flow events spread through out the year

3. Reallocate some storage to different project purposes.

4. Better define how to implement future maintenance activities into the operations plan. This may include lowering the water surface elevation to 1110 feet every 10 years, or as needed, to allow the Corps to inspect the upper conduit of the dam’s outlet works.

Figure 1. Diagram of the major structures of Alamo Dam.

 

Figure 2. Existing reservoir storage allocations for the three defined purpose water pools – flood control,
 flexible operations [previously water conservation], and recreation.

 

Table 1. Existing Riparian Release Schedule, please note once the lake elevation enters the flood control
 pool releases up to 7,000 cfs will be made until the pool is back to the target elevation.

 

What things aren’t likely to be changed in the Water Control Plan?

1.  Corps maintenance of a minimum 10 cfs average release for downstream water rights and riparian base flows.

2. The maximum release possible through the outlet works is 7,000 cfs.

3. Maintaining flood control releases when the reservoir is in the flood control pool, barring unusual downstream constraints.

4. Operation for fish and wildlife benefits should not reduce flood control or recreation benefits.

5. Bulkhead can only be installed when elevation ≤ 1110 ft and putting the bulkhead gate in place must be placed to inspect the Dam’s upper conduit.

6. The Corps must be able to conduct routine inspections (i.e. upper conduit, gate maintenance, etc.) at a scheduled interval.  The interval must be short enough to allow reasonable confidence in the operational functionality of the Dam.

7. The Corps must operate the Dam in a way to minimize the potential for the probable maximum flood to overtop the Dam.