Central Alabama Water Advances Lake Purdy Dam Rehabilitation wiht Additional investigations
Central Alabama Water (CAW) is undertaking a $28 million, multi-phase project to rehabilitate the Lake Purdy Dam, originally constructed in 1909 adn raised in 1929. The current Phase 1 focuses on strengthening the dam’s structure with roller compacted concrete. Recently,the CAW board approved three additions to the ongoing work,aimed at a comprehensive assessment and reinforcement of the historic dam.
These additions include a dye test to identify potential seepage pathways, exploration drilling on the dam’s left (downstream) side, and the installation of a deep foundation utilizing micro piles on the right side. schnabel Engineering will conduct a reservoir dye test as early as next week,releasing two non-toxic,biodegradable,and NSF-approved dyes upstream. Engineers will monitor the downstream area for three hours to observe dye movement, potentially resulting in temporary discoloration of the Little Cahaba and Cahaba Rivers. Officials emphasize this poses no risk to the river ecosystem or drinking water,as water from the Cahaba River undergoes filtration and treatment at the Shades Mountain Filter Plant.
The exploration drilling on the left side of the dam will confirm geological conditions and is expected to take one to two days at a cost of approximately $25,000. Together, engineers will begin installing a deep foundation on the right side, involving drilling, inserting steel pipes filled with rebar and concrete, and capping with a concrete slab. design for this foundation is anticipated to take two weeks,with construction slated for completion by the end of December.
CAW Vice-Chairman Phillip Wiedmeyer, a retired engineer, highlighted the importance of the project, stating it’s a “generational opportunity” to ensure the dam’s continued service to customers. he further explained the rationale behind the additional exploration, noting that conducting it before concrete is poured allows for informed decision-making at minimal expense.
Despite the ongoing work, CAW assures the public that Lake Purdy Dam remains safe. As of October 17th, the reservoir was nine feet below full capacity due to typical late summer/early fall dry conditions. Officials stated that over seven inches of rainfall within a 24-hour period – equivalent to a 25-year storm – would be required for water to reach the dam’s crest,indicating a low risk of overflow.
The board has postponed a vote on engaging an outside expert for a separate review of the dam’s overall health.