AGENDA CAPTION:
Title
Consider approval by motion of Change in Service #5 in the amount of $94,775; for Professional Engineering Services in Connection with 2D Model Enhancement and 2015 Blanco Flood Analysis (Contract #216-076), with, Halff Associates, Inc. for providing engineering services to update the 30% storm drain system within the TxDOT right-of-way.
Body
Meeting date: November 20, 2018
Department: Engineering/CIP
Amount & Source of Funding
Funds Required: $94,775
Account Number: C629
Funds Available: $600,000
Account Name: IH-35 Utility Relocations
Fiscal Note:
Prior Council Action: NA
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Stormwater
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Background Information:
The attached Change in Service #5 to Halff Associates, Inc. in the amount of $94,775 will provide engineering services required for the analysis of the storm drain system within the TxDOT right-of-way for IH-35 from north of Ranch to Market (RM) 12 (Wonder World Drive) to south of State Highway (SH) 80 (Hopkins Street) in San Marcos, Hays County, Texas as identified in the TxDOT schematic dated June 2017.
TxDOT proposes to improve the frontage roads, ramps, and select locations of the main lanes within the project limits of approximately 2.5 miles. The Engineer will update the 30% plan set from the existing 10-year design to the ultimate 25-year design to correspond with the betterment improvement to the TxDOT storm drain system. These updates will allow offsite flows from Sunset Acres for an Ultimate (fully developed) 25-year storm event to safely be conveyed through the TxDOT right-of-way. Scope of work includes:
• Project Management: perform general project management and coordination during the course of the project
• Storm Drain Analysis: Obtain information regarding existing and proposed drainage from off-site areas outside of the TxDOT right-of-way from the City of San Marcos. This information may include drainage studies for Clairwood Area, Sunset Acres Area, COSM Comprehensive Drainage Master Plan, Cottonwood Creek 2D H&H Analysis, and/or other areas the City may have knowledge about. The Engineer will utilize this off-site information develop by others as part of the analysis for the potential storm drain system upgrade.
• Storm Drain Design: Analyze and size trunk lines, ditches, and outfalls to safely convey the Ultimate (fully developed) 25-year storm event as non-pressurized flow. Analysis shall minimize the interference with the passage of traffic or incur damage to the highway and local property in accordance with TxDOT’s Hydraulic Design Manual, District criteria and any specific guidance provided by TxDOT. Size the inlets to intercept the 25-year storm event. Inlet spacing and spread criteria will be based on the TxDOT 10-Yr design. Structural design of oversize junction box or RCB tee to equalize flow between dual box culverts. Update the 30% plan set the betterment design the cost estimate
Although a new contract with Halff Associates, Inc. is required to complete the 30% storm drain design within TxDOT right-of-way, however it will take much longer time to execute a new contract. Therefore a CIS#5 to the existing contract #216-076 i.e. “Professional Engineering Services in Connection with 2D Model Enhancement and 2015 Blanco Flood Analysis” is requested to accommodate the aggressive project schedule proposed by TxDOT (design completion by June 2019). The amount requested to complete additional tasks will be funded from C629, i.e. IH 35 Utilities Relocations.
Council Committee, Board/Commission Action:
NA
Alternatives:
NA
Recommendation:
Staff recommends approval of CIS#5