One Less Thing to Worry About in Latest Storm: How Seasonal Lowering of Lake Conroe Helped

Storms during the last two days were traumatic for virtually everyone in the Kingwood area. Tragically, one person lost her life when her car hit a downed tree.

  • Others lost vehicles, trees, and sleep.
  • Torrential rains for a brief period – at the rate of 4-5 inches in an hour – flooded streets and vehicles.
  • They also brought water near or into homes.
  • Parents picking children up from school waited in rising waters as their students sheltered in place.
  • A small tornado may have briefly touched down near Town Center.
  • Kingwood Drive was shut down for hours during the Friday afternoon rush hour.
  • People traumatized by Harvey were re-traumatized.
  • People without power waited and wondered for hours about what was going on around them.

Lake Conroe: One Less Worry This Time

Despite all that, we did NOT have to worry about one thing: Lake Conroe opening its flood gates again during this storm. The seasonal lowering policy established last year worked.

The SJRA board voted to lower the lake’s level one foot to 200 mean feet above sea level (MSL) from April 1 to May 31.

That action may have saved the Lake Houston area from additional flooding in the last round of storms.

Releasing Water Continuously At Low Rate Created Extra Capacity

Lake Conroe had released water continuously since April 1 at a slow, controlled rate of 350 to 550 cubic feet per second. However, because of spring rains, Lake Conroe had only dropped about a half foot from 201 to 200.66 feet MSL. Had the releases not happened, the lake would have been an estimated 1-1.5 feet higher, according to Mark Micheletti, an SJRA board member from Kingwood. That means the lake level would have been approaching 202 feet, the level at which the SJRA automatically begins releasing water, when the storm hit. That would have forced the SJRA to release water at a higher rate that could have overloaded the downstream watershed.

Buffer Against Downstream Flooding Worked

In other words, the policy worked. The seasonal lowering provided a buffer against downstream flooding. NOAA shows a double crest on the San Jacinto West Fork at US59 during the last two days that coincided with two waves of storms. At peak flow, the river came within about two feet of going out of its banks.

An additional foot of water released from Lake Conroe would have added two feet to Lake Houston and created flooding.

About a mile downstream at River Grove Park, the water was up, but still within its banks.

Despite torrential rains last night and early this morning, the West Fork remained in its banks. The river was up, but no homes flooded from the river.

Success: No Rivers or Streams Out of Banks

At this hour, neither NOAA, the SJRA, nor Harris County Flood Control, predicts any flooding from yesterday’s storms. In fact, all streams and bayous seem to be receding at this time. That’s one less thing to worry about as we clean up from the latest storm. The SJRA’s seasonal lowering DID help.

Remember, Lake Conroe is almost twice as big as Lake Houston (33 sq. mi. vs 18.5 sq. mi.). So one foot released there translates into almost two feet here. And two feet would likely have forced the San Jacinto out of its banks for the fifth time in a year.

Kudos to the SJRA board, the City of Houston, and the TCEQ for enabling this policy. That, in conjunction with the City’s pre-release policy for Lake Houston, have made a difference.

Posted by Bob Rehak on 5/5/2019

614 Days since Hurricane Harvey

Street Flooding vs. River Flooding

During Harvey, most of the damage in Kingwood happened from river flooding. Yesterday, it happened from street flooding. What are the respective causes? Differences? Fixes?

River Grove Park the morning after the street flooding during the previous day and night. The river was still well within its banks and is not predicted to come out.

River Flooding Overview

River flooding happens when heavy rainfall exceeds the conveyance capacity of a river. In other words, the river comes up and out of its banks. This happened to the San Jacinto during Harvey. The river, normally a couple hundred feet wide, became three to four miles wide, inundating miles from the main current.

River flooding can be caused by heavy rain, upstream snow melt, dam/levee breaks, dam releases, and more. Most commonly, it takes hours to days for water to work its way through a river system and affect people downstream.

River Flooding Remedies

Fixes for river flooding include things like:

  • Building dams upstream to reduce the flow downstream.
  • Increasing the conveyance of the river through widening, deepening or dredging
  • Removing blockages such as the mouth bar on the West Fork of the San Jacinto
  • Increasing the outflow capacity, for instance by adding gates to dam
  • Building levees
  • Diverting water to tunnels.

Street Flooding Overview

Street flooding, on the other hand, is often much more local and happens over shorter periods of time. It is often referred to as flash flooding because it comes up quickly and goes down quickly. That’s what the Lake Houston Area experienced yesterday. The San Jacinto, its tributaries and drainage ditches were and still are well within their banks.

Flash flooding occurs when the rainfall RATE temporarily exceeds the drainage capacity of storm drains, sewers, swales, and ditches that lead to rivers.

Yesterday, we received 1/20th the amount of rainfall that we did during Harvey, but many people reported the water coming up higher. That’s because storm sewers could not handle the intense rainfall that happened during approximately a one hour period.

Drains on Valley Manor could not handle the sudden surge.

Streets Designed as Part of Flood Retention System

The streets in Kingwood (and most cities) are actually designed to be part of the flood retention system. When developers excavate streets, they often use the fill to build up homesites. By increasing the elevation difference between street level and your foundation, they reduce the chances that you will flood.

They size the sewers so as not to make drainage ditches overflow. Rainfall rates like we experienced yesterday don’t happen for very long. The storm passes. The water in the street goes down and life returns to normal. You just don’t want to be caught out on the road in your car when it happens. Nor do you want to have your car parked on the street!

Street Flooding Remedies

The Greater Houston Flood Mitigation Consortiums’ report on Harvey contains an extensive discussion of the different types of flooding. Their discussion of street flooding starts on page 14. Page 15 identifies solutions, including:

  • Communicate the role of streets in the drainage system. Many residents may not be aware that roads are intended to act as a secondary short-term storage system and/or conveyance pathway for water. This can lead to severe property damage and loss of life when residents do not move property out of harm’s way. For example, recent street flooding has caused severe flooding of cars, which are frequently parked in the street. It is also important to note that 12 inches of water can float a sedan and 18-24 inches can float a larger vehicle, creating hazardous road conditions during extreme events. It is critical to develop a strategy to communicate to the public that streets are designed to be a secondary short-term storage system so that people can take action to prevent loss of property and life. 
  • Address debris in streets and waterways. Maintaining clear openings to storm sewer inlets is a great way to help reduce street flooding. Flooding in many neighborhoods can be made worse by debris and floating trashcans that clog inlets. Additional city, county and MUD maintenance, or organized community efforts may be required. 
  • Ensure that developers have sufficient “upstream” information. Land development engineers typically focus on mitigating the runoff generated by their development project, and as such, flows entering onto their site from other sources may not be considered in their design analysis. Examining strategies to share information about upstream conditions with developers during the design analysis phase could help maximize site-based mitigation. 
  • Maximize on-site retention. Green infrastructure may provide a viable alternative for managing stormwater and reducing nuisance flooding through implementing on-site retention or by providing additional in-line storage capacity within the street (examples include Cottage Grove and Bagby Street). 
  • Identify & target high-risk areas. Determining the neighborhoods most vulnerable to flooding from local drainage challenges would be a pivotal step to targeting public education and mitigation strategies. 

For More Information

The flooding yesterday happened so quickly that it scared people. For many, it brought back vividly the trauma of Harvey and the pain that followed. One person even died when her car ran into a downed tree that fell across Kingwood Drive.

The most damage happened, not to homes, but to vehicles caught in high water on flooded streets – streets DESIGNED to hold water. There’s a simple answer to that. Unfortunately many people did not get the warnings that could have kept them off the streets.

For more information on different types of flooding, see the first part of this FloodWarn Training Seminar that Katie Landry-Guyton of the National Weather Service presented last year at Kingwood College.

Posted by Bob Rehak on 5/4/19

613 Days since Hurricane Harvey

Overnight Rains Could Add to This Afternoon’s Woes

A strong line of thunderstorms with high winds, torrential rains and possible tornadoes swept through the Lake Houston area this afternoon. It left widespread power outages, snarled traffic, flooded streets, and swollen creeks and ditches. People still suffering PTSD from Harvey were re-traumatized by the sound of news helicopters and water creeping up their front steps. More heavy rains tonight will add to the area’s woes, even as people are still cleaning up from this afternoon’s flooding.

Examples of Damage Reported

Among the damage reported:

  • Several flooded homes in Bear Branch and Woodland Hills near creeks or ditches
  • Flooded locker rooms at Kingwood High School
  • Trees down and blocking Kingwood Drive at rush hour
  • Power lines down on Kingwood Drive
  • Knee-high water on Kingwood Drive at Town Center
  • Kingwood Drive traffic rerouted up Valley Manor
  • New pad sites for the retail expansion of the HEB center under water
  • Street flooding from one end of Kingwood to the other

Streets Designed as Part of Flood Retention System

Note: the streets in Kingwood are DESIGNED as part of the flood retention system. When rainfall rates exceed what creeks, ditches and bayous can handle, water backs up into streets. and drainage swales.

The amount of rain we received today was not great. But the intensity was off the charts. In about a half hour at my house, we received almost two inches. That’s between 3 and 4 inches per hour. Here’s an example: the swale beside my house.

Valley Manor just north of Kingwood Drive at 4PM on 5.3.19. Two neighbors across the street reports water on their front steps. One said water started to come through her front door. The family is still repairing from Harvey. Her entire family is traumatized.
This is the ditch adjacent to the retail expansion of the H-E-B center. Photo courtesy of Mark Micheletti.
Kingwood Drive west of Town Center. Photo courtesy of Clay Crawford.
Kingwood Drive at Town Center.Photo courtesy of Clay Crawford. I heard that the entrance to Fosters Mill was also under water.
Video of street in Riverchase by John Knoerzer.

Rainfall Totals for Friday Storm

Rainfall totals for last 24 hours as of 10PM 5.3.19. Note higher totals upstream from Lake Houston area.

River Report: Minor Flooding Possible on West Fork

Harris County Flood Warning System’s Real Time Inundation Mapping shows most streams within their banks. But note the warning for Humble at US59. While the river is 2 feet below the top of bank as of 10PM, it could easily go out of bank tonight.

More Storms on Way

As of 9PM a severe thunderstorm watch is still in effect for much of southeast Texas until 3PM Saturday.. A large line of strong to severe thunderstorms has developed from E of Austin to NW of San Antonio and is moving ESE/SE at 15-20mph. Expect an average 1-2 inches with the line passage. Isolated total up to 3 inches be common. Creeks and bayous should be able to handle that amount of rainfall, according to Jeff Lindner of Harris County Flood Control.

NOAA forecast clearly shows the line of strong thunderstorms that should hit us overnight.

Here is an updated radar image as of 12:01 AM Saturday morning.

Image courtesy of RadarScope, an amazing app!

Expect minor flooding at 59 and River Grove Park, that could be exacerbated by the mouth bar and other sediment still in the river.

This does not account for any local effects to the mouth bar.

Hoping you stay dry!

Posted by Bob Rehak on 5/3/19 around midnight

613 Days since Hurricane Harvey