Projects & Studies

As of 10/15/2019

Z-08 Preliminary Engineering Study for Large Diameter Tunnels for Stormwater Conveyance

Project Description

This short-term study was intended to take a high-level look at the feasibility of potentially constructing large diameter deep tunnels to help move stormwater out of Harris County. The study was the first phase of a multi-phased approach to look at soil types, geotechnical challenges specific to Harris County, hydraulic capacity and impacts, scheduling and cost projections, and compare conditions in Harris County with other active and completed tunnel projects around the United States and the world.

> Phase One Final Report

Phase One findings include but are not limited to:

  • Geotechnical conditions do not appear to present any remarkable nor non-negotiable concerns.
  • Geologic faults may require special design and construction considerations if crossed by the tunnel; not considered fatal flaws.
  • Tunnels can move a significant rate of stormwater operating by gravity as an inverted siphon.
  • Tunnel cost, including a 50% contingency, for a representative 10-mile-long, 25- and 40-foot diameter tunnel is approximately $1 billion and $1.5 billion respectively

Harris County Flood Control District funded this study through a $320,000 grant from the U.S. Economic Development Administration and an $80,000 cost-share from the HCFCD 2018 Bond Program.

Harris County Flood Control District worked with experts from Freese and Nichols, Parsons, Brierley Associates, Terracon, HVJ, Sowells Consulting Engineers and Middleton Brown for this study.


This phase one study was not watershed specific nor scoped to focus on any particular alignment/location.


This project is currently in the FEASIBILITY STUDY phase - completed phase 1. 

> Learn more about our project lifecycle 


Total allocation for this multi-phase project is currently $20 million on the Bond Project List.

> Download the Bond Project List

Project Milestones

Fall 2019 – Request for Statements of Qualifications for Phase 2 of the Feasibility Study expected to be published by Harris County Purchasing.

September 30, 2019 – Final Report submitted to Department of Commerce, Economic Development Administration for review.

September 23, 2019 – Final Report delivered to HCFCD.

September 17, 2019 – Initial Project Criteria report completed.

August 22, 2019 – Preliminary Inverted Siphon Analysis completed.

August 16, 2019 - Preliminary Tunnel Cost Analysis completed.

August 16, 2019 – Preliminary Geotechnical Desktop Study completed.

August 15, 2019 - Preliminary Opinion of Tunneling Applicability completed.

June 25, 2019 – Houston Faulting Workshop held with local fault experts.

June 10, 2019 – Project Kickoff meeting with project consultant held.