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City of Houston Re-evaluating Benefit-Cost Ratio on Lake Houston Gates Project Alternatives

According to minutes of the Coastal Water Authority (CWA) February 9 board meeting posted in March, work on the project to add more gates to Lake Houston was paused in January while the City of Houston updated the project’s benefit-cost ratio.

gates for Lake Houston and Conroe
Lake Houston and Lake Conroe gates side by side. Lake Conroe’s gates (right) can release water 15 times faster.

CWA Board Minutes Give High-Level Overview of Concerns, Status

Screen capture from CWA Feb. 9, 2022, minutes approved and posted in March.

Earlier, in December, the board learned that the project team was trying to get the benefit/cost ratio above 1.0, so benefits exceed costs.

Screen capture from CWA January 12, 2022, board minutes.

At that time, the CWA hoped to receive the updated BCR later in January. But it still hadn’t happened by the February board meeting.

Martin Says “September-ish” for BCR Report

City of Houston Mayor Pro Tem Dave Martin said he hopes to have the BRC report in a “September-ish” time frame. I asked him whether the Community Impact report was accurate when it said the project had been scaled back to 500 feet of crest gates as opposed to the original 1500 feet. He said “no,” and that the engineers were looking at multiple options. He also said “1.0 is incorrect as well,” but did not elaborate.

That leaves a lot of questions regarding this project.

History of Project

After Harvey, the Lake Houston Area Task Force identified adding additional gates to Lake Houston as one of three primary strategies to reduce flood risk in the Lake Houston Area. The idea: to equalize the discharge rates of the flood gates on Lake Houston and Lake Conroe. Conroe’s is 15X greater. That makes it difficult lower both lakes quickly in advance of approaching storms.

As a temporary strategy, the City and SJRA agreed on a temporary, seasonal lake lowering strategy to create more capacity in Lake Conroe until more gates could be added to Lake Houston. But the strategy met with significant pushback from Lake Conroe residents and lawmakers. The Lake Conroe Association even took the SJRA to court to stop it.

At various times, City representatives have discussed 10 and 6 additional tainter gates, plus 1500-, 1200-, and 1000-feet of crest gates. Engineers and City officials have repeatedly emphasized the need to balance costs, downstream impacts, and flood risk reduction.

Back in October 2020, the engineers calculated that the upstream influence of the dam ended at approximately Lake Houston Parkway. But they never explained why. It would seem that if the influence extended upstream to US59 when the lake is at its normal level, that the influence should extend at least that far in a flood. However…

BCR Not Based on Harvey Damage

Much of the damage to the Humble/Kingwood Area during Harvey happened upstream of the West Lake Houston Parkway Bridge. It included:

  • $60 Million to Kingwood College
  • $70 million to Kingwood High School
  • $50 million to Kingwood County Club
  • 283 homes in Barrington
  • 218 homes in Kingwood Lakes
  • 97 apartments in Kingwood Lakes
  • 110 homes in Kings Forest
  • 100% of businesses in Kingwood Town Center
  • 225 homes in Kingwood Greens
  • 30 homes in Deer Cove
  • 3 Homes in Deer Ridge Estates
  • 32 homes in Trailwood Village
  • An unknown number of homes in Forest Cove
  • 78 townhomes in Forest Cove
  • All of the Big Box stores along 59
  • Homes and business north of Deerbrook mall
  • 40% of all businesses in the Lake Houston Chamber
  • Humble ISD admin building
  • Destruction of US59 southbound lanes
  • Union Pacific Railroad Bridge

However, Black & Veatch does not base its benefit-cost ratio calculations on another Harvey. They’re basing it on 25- and 100-year storms. Almost all homes, businesses and infrastructure near the lake are already above those levels – at least based on pre-Atlas 14 standards. That may explain the difficulty and delays with benefit/cost ratio calculations and the multitude of scenarios examined.

Time, Uncertainty: More Factors to Consider in Cost and Risk Reduction

Each flood-risk reduction alternative would reduce lake levels by a different amount during a 100-year storm and therefore require its own BCR.

Other factors to consider: How much time do dam operators really need to lower Lake Houston? And how much uncertainty are they willing to live with?

Given the desire to preserve water, these are crucial considerations. If forecasters can reliably predict a need to lower the lake two days before a storm instead of one, operators may only need half the number of new gates. That could get the cost down to the point where the benefit-cost ratio needs to be.

But don’t forget another element of uncertainty: Atlas 14. FEMA has not yet approved the new flood maps based on the higher rainfall totals. Those could put more people in or closer to the floodplains. Below is the timetable for flood map updates currently posted on the MAAPnext website.

Timetable for flood map updates from MAAPnext.

Posted by Bob Rehak on 4/4/22 and updated on 4/5/22 with MAAPnext timetable

1679 Days since Hurricane Harvey