Risk Reduction Spillway and Dam Safety Modifications at Lower Beaver Brook

August 26, 2018 by  
Filed under Dam Safety @ LBB - 2018

Comments Off on Risk Reduction Spillway and Dam Safety Modifications at Lower Beaver Brook

Project Summary and Status Update – June 2019

The Lookout Mountain Water District (LMWD) has received assistance from FEMA to address identified dam safety deficiencies at the Lower Beaver Brook Dam, pursuant to the National Environmental Policy Act (NEPA), Section 106 of the National Historic Preservation Act (NHPA), Executive Order (EO) 11988 – Floodplain Management, and EO 11990 – Wetland Protection, and Federal agency implementation procedures, including 44 CFR Part 9 and FEMA Directive 108-1.

FEMA funding will be provided through the Pre-Disaster Mitigation Program (PDMC-PJ-08-CO-2017-002), which provides funds for the planning and implementation of long-term hazard mitigation measures prior to a disaster event. The purpose of the PDM program is to implement cost-effective mitigation projects that will reduce the overall risk to populations and property.  In accordance with NEPA, an Environmental Assessment (EA) was prepared to evaluate the potential impact of the proposed project on the human and natural environment and has issued a Finding of No Significant Impact (FONSI). Appropriate mitigation measures will be implemented in accordance with EO 11988 and Section 106 of the NHPA.

The proposed project includes addressing the identified dam safety deficiencies at Lower Beaver Brook Dam by replacing the existing 114-year-old rockfill embankment dam with a new concrete gravity dam. The proposed Lower Beaver Brook Dam will be designed and constructed to be in conformance with the State of Colorado Division of Water Resources, Dam Safety Branch Rules and Regulations for Dam Safety and Dam Construction. The new concrete dam will be constructed immediately downstream of the existing dam and will not result in additional storage capacity or increased discharges during routine flow conditions.

Request for Proposals for Consulting Engineering Services for Design and Construction Management of the Lower Beaver Brook Dam Project:

The District plans to publish a Request for Proposals (RFP) on July 24 and July 31, 2019.  A mandatory pre-proposal meeting is currently scheduled for 10 a.m. on August 6, with the tentative due date for RFP submittal on August 28th (these dates are subject to change, please confirm after publication).

Draft Environmental Assessment:

0. Lower Beaver Brook Dam_EA_Final Draft 5 21.rm

EA Appendices:

pg1-42 1. Lower Beaver Brook Dam Appendices A-B 5 21

Appendix C – Agency Correspondence_cs

Appendix D – 8-Step Decision-Making Process

Reference Documents:

1 of 3 – Wheeler, 2017-1_Alternatives Analysis Report – Lower Beaver Brook Dam_Oct 2, 2017 thru Appendix A

2 of 3 – Wheeler, 2017-1 Alternatives Analysis Report Appendix B due to file size restrictions must be requested.

3 of 3 – Wheeler, 2017-1_Alternatives Analysis Report – Lower Beaver Brook Dam_Oct 2, 2017

Project Summary and Status Update – March 2019

The Lookout Mountain Water District continues to work on the Lower Beaver Brook Dam Safety Modifications Project. The District applied for grant funding of $3.9 million for the project through the national Pre-Disaster Mitigation Program. The purpose of this program is to implement cost-effective mitigation projects that will reduce the overall risk to populations and property.  The dam is over 100 years old and its spillway is undersized, so it must be replaced to ensure that the District will have a secure supply of water for the treatment plant and to reduce risk of failure during flooding. District residents will be responsible for funding the remaining cost of the project (current estimated total project cost is $5.3 to 6.2 million).

FEMA has issued an eligibility notice in 2018 and expects to award the grant in mid-2019, then design and permitting can be completed in 2020 with construction to follow in 2021.  The project is currently under review for environmental and historical preservation.

Primary Participating Agencies —

Federal Emergency Management Agency  (FEMA)

Colorado Division of Homeland Security and Emergency Management (CDHSEM)

Colorado Division of Dam Safety

Colorado State Historic Preservation Office

Colorado Water Conservation Board

U.S. Army Corps of Engineering

Jefferson and Clear Creek Counties

 

PRE-DISASTER MITIGATION PROGRAM FUNDING

FEMA is considering funding a portion of the proposed project through the Pre-Disaster Mitigation Program (PDM), which provides funds for the planning and implementation of long-term hazard mitigation measures prior to a disaster event. The purpose of the PDM program is to implement cost-effective mitigation projects that will reduce the overall risk to populations and property.  In accordance with NEPA, an EA will be prepared to evaluate the potential impact of the proposed project on the human and natural environment.  A portion of the project will be funded by LMWD. The State of Colorado Office of Emergency Management will oversee the administration of the grant funding.

DAM SAFETY SUMMARY

The proposed project includes addressing the identified dam safety deficiencies at Lower Beaver Brook Dam by replacing the existing 114-year-old rockfill embankment dam with a new concrete gravity dam. The modified Lower Beaver Brook Dam will be designed and constructed to be in conformance with the State of Colorado Division of Water Resources Dam Safety Branch Rules and Regulations for Dam Safety and Dam Construction. The existing 114-year-old rockfill dam will be removed in stages throughout the construction of the new concrete dam.

The new concrete dam will be constructed immediately downstream of the existing dam. The new concrete dam will have a non-overflow dam crest at each end, with a central emergency spillway. The existing service spillway on the right abutment will be rehabilitated to maintain the existing normal pool elevation of about 7837.7 because maintaining this normal high-water line is important for maintaining water storage for drought protection, operation of the Water Treatment Facility, and for avoiding long-term environmental impacts to habitat and wetlands in the reservoir area. The new structure will not result in additional discharges in the downstream floodplain during routine flow conditions.