Item 10 - Lake Surveys — original pdf

Backup

Item 10 Water & Wastewater Commission: May 21, 2025 Council: June 5, 2025 ..Title Posting Language Recommend approval to authorize negotiation and execution of an Interlocal Agreement with Texas Water Development Board (TWDB) for Sedimentation and Bathymetric surveys of Lake Austin and Lady Bird Lake for a total contract amount not to exceed $107,038. Funding in the amount of $107,038 is available in the Fiscal year 2024-2025 Operating budget of Austin Water. ..De Lead Department Austin Water. Prior Council Action: 8/7/2008 - Council Approved - Authorize negotiation and execution of an Interlocal Cooperation Agreement with the Texas Water Development Board (TWDB) for a volumetric survey of Lake Austin, in an amount not to exceed $20,628. 8/7/2008 - Council Approved - Authorize negotiation and execution of an Interlocal Cooperation Agreement with the Texas Water Development Board (TWDB) for a volumetric survey of Lady Bird Lake, in an amount not to exceed $19,981. 2/25/2010 - Council Approved - Authorize negotiation and execution of an Interlocal Cooperation Agreement with the Texas Water Development Board (TWDB) for a volumetric survey of Lake Austin, in the total amount of $5,157. Note - This Agreement applies to the portion of the original contract that has not already been paid to TWDB in the amount of $5,157.00. 2/25/2010 - Council Approved - Authorize negotiation and execution of an Interlocal Cooperation Agreement with the Texas Water Development Board (TWDB) for a volumetric survey of Lady Bird Lake, in an amount not to exceed $4,995.25. Note - This Agreement applies to the portion of the original contract that has not already been paid to TWDB in the amount of $4,995.25. Council Committee, Boards and Commission Action: May 21, 2025 - To be reviewed by Water and Wastewater Commission. Additional Backup Information: The Texas Water Development Board (TWDB) will perform a sedimentation and bathymetric survey of Lake Austin and Lady Bird Lake. A bathymetric survey will entail collection of bathymetric or depth measurements to develop an updated elevation-area-capacity table and associated contour maps. While a bathymetric survey only identifies the current bottom surface of a reservoir, a TWDB sedimentation survey identifies the pre-impoundment surface of the reservoir as well. Sediment core samples are collected throughout the reservoir and correlated with multi-frequency acoustic data signal returns to aid in the identification of the pre-impoundment surface. A sedimentation survey report includes updated elevation- area-capacity tables, a bathymetric contour map, a sediment volume and annual average sedimentation rates, and a map of sediment thicknesses throughout the reservoir. These surveys will also include three dimensional scans of Austin water intake structures at Ulrich Water Treatment Plant, Davis Water Treatment Plant, and the abandoned intake structure at the decommissioned Green Water Treatment Plant. The last bathymetric survey of these lakes was completed in 2008. An updated survey will provide information relating to accumulation and loss of sediment in creek deltas and along the lakeshore, as well as change in lake volume. The most recent survey did not include sedimentation survey and the scans of water treatment plant intakes. This data will inform water resource projects to meet the needs outlined in Water Forward, Austin Water’s 100-year integrated water resource plan and other water resources planning efforts.