River Grove Park

All Floodwaters Receding, But Flood Warnings Remain in Effect

1/28/24, 2PM – After a week of near-constant rain and flooding, all river and lake gauges in the area show floodwaters receding, even if they aren’t below flood stage yet.

Whew! If you didn’t flood, you can stop worrying.

Nevertheless, the National Weather Service (NWS) still has flood warnings in effect for the areas:

  • Near the San Jacinto East Fork at FM1485 in New Caney. The warning affects people in Montgomery, Harris and Liberty Counties. Expect moderate flooding, primarily in low lying areas through Tuesday. The river is currently at 62′; flood stage is 58′ at that location.
  • West Fork around US59 until Monday afternoon. The river was at 51.4 feet, but bankfull is 45.3 feet.
  • Around Sheldon, below the Lake Houston Dam until tomorrow morning.

Photos Before, During, After Flood Crests

Below are 18 pictures I and a reader (who prefers to remain anonymous) took this week shortly before and after flood crests arrived. Each is dated and appears in chronological order. Together, they give you an idea of the extent of flooding. People who live in low-lying areas near major rivers were most affected.

But others, still suffering PTSD from previous floods, watched and waited with a sense of impending doom, wondering whether the water would claim their homes. It was a week of high anxiety and sleepless nights for many.

East Fork at Plum Grove

FM2090 over East Fork San Jacinto at Plum Grove. Thursday, 1/25/24.

It was hard to tell where the East Fork was at times. The river had penetrated an adjacent sand mine in multiple places and was flowing through it.

East Fork (upper left) broke through dike of abandoned sand mine and started flowing through it. Thursday, 1/25/24.
Rising water flooded the sand mine and isolated an adjacent house. Thursday, 1/25/24.
Looking west toward West Fork across Northpark South. Despite the ditch that contractors dug to drain the wetlands, a lot of water is still ponding. Thursday, 1/25/24.

West Fork in Humble/Kingwood Area

On Friday, 1/26/24, rising West Fork floodwaters near US59 invaded the neighborhood north of the bridge.
West Fork at US59 on Friday, 1/26/24. Rising water flooded turnarounds under the freeway on both sides of the river.
Friday, 1/26/24. Confluence of West Fork (right) and Spring Creek (left). Contrast enhanced to show that flow came predominantly from West Fork at this time.
Saturday 1/27/24. Homes isolated by floodwaters just south of New Caney ISD’s New West Fork High School (upper right).
Looking west, farther downstream on the West Fork at homes along Lake Point and North Shore Drives.
Saturday 1/27/24. KSA River Grove Park parking lot, boardwalk, and bridge to soccer fields were all under water.
Saturday 1/27/24. Golf course near Barrington subdivision flooded.
Saturday 1/27/24. Edgewater Park at US59 and West Fork partially underwater.
Kingwood County Club’s Forest Course becomes a Water Course south of Kingwood Greens subdivision.
At Kings Harbor on Saturday 1/27/24, water topped the pier, and the riverwalk, but didn’t get into businesses.
Sunday, 1/28/24. Looking at West Fork and adjacent sand mines from Northpark Woods. Note multiple breaches in dikes of two abandoned sand mines. Photo courtesy of reader.
Sunday 1/28/24. Courtesy of reader. Looking west past Northpark Woods (lower right). Note level of water in ditch. Google Earth measurement shows the water extends more than 3,000 feet up the ditch. That’s more than half a mile.
Farther up the ditch, you can see silty water from the mines on left and right mixing with water in the ditch. Photo courtesy of same reader.

Takeaways from Flood

I took several things away from this experience.

  1. Sediment mainly moves during floods. It’s too early to tell how much moved and whether it will be enough to impair the conveyance of rivers, bayous, creeks and ditches. But this flood represents a major opportunity for the engineers conducting the SJRA’s sedimentation study.
  2. Even relatively small amounts of rain (a couple inches per day) caused some major heartburn.
  3. The SJRA’s modeling nailed the flood peak on the West Fork. Even when the National Weather Service was predicting a peak in the 52′ range at US59, the SJRA said it would be 53.5′. The actual peak was 53.71, within tens of an inch.
  4. SJRA claimed the rainfall in the Lake Creek watershed was a major contributor. They don’t control that. It joins the West Fork downstream from the Lake Conroe Dam. A gage on Lake Creek showed 9.8 inches fell there in five days – among the highest totals for the region.
  5. The recent freeze killed a lot of vegetation that would normally have slowed runoff. That contributed to faster, higher peaks, according to testimony given during the SJRA board meeting last week.
  6. The SJRA did a much better job of communicating its gate operations to the public during this storm than ever before. It sent out a stream of press releases explaining what it was doing and why. I even received a personal call from an SJRA board member at 9pm before they increased their release rate to 19,500 cfs.
  7. The timing of the calls to news media got the news of the release on the 10 o’clock news before people went to bed. During Harvey, that didn’t happen. Many people were caught sleeping in bed by rising flood waters and had to evacuate by boat. Lesson learned.
  8. We need to do a damage assessment both upstream and downstream from the Lake Conroe dam to see where damage was concentrated. Did the SJRA do a good job of balancing upstream and downstream interests? Could gate operations have been improved?
  9. The SJRA says it waited to release water until it got within 6 inches of the top of its tainter gates. Had the water gone over the top of the tainter gates, they could have lost control. The gates would have become inoperable and the dam could have been placed in jeopardy.
  10. One leading hydrologist told me, “Understanding watershed hydrology is difficult. It rained quite a bit over a very large area. Watersheds all respond differently. The timing of the runoff reaching channels is crucial. How it combines with all of the other runoff from different places is key.”
  11. We need more floodgates on Lake Houston.

The worst of this event is behind us. Now comes the hard part. Cleaning up.

I wasn’t able to cover every area that flooded during this event. So, if you have photos of the flood or its impact that you would like to share, please submit them through the contact page of this website. Understand that all photos used here are in the public domain and may be shared by others. Finally, please indicate whether you would like a picture credit, and if so, how it should read.

Posted by Bob Rehak on 1/28/2024

2343 Days since Hurricane Harvey

How bad was that rain.

How Bad Was That Storm?

A week of rain has ended. Flood crests are passing. And many are asking, “How bad was that storm?”

The short answer to the question: depending on where you live in the region, you got a 1- to 5-year rainfall.

Why is that? And how do you determine it? It’s simple. Let’s start with the rainfall.

Step One: Determine the Amount of Rainfall You Got

If you don’t have a rain gauge, go to the Harris County Flood Warning System. Elsewhere in Texas, you can go to the Texas Water Development Board’s Mesonet.

For demonstration purposes, let’s focus on the Harris County Flood Warning System.

By default, the home page shows a map with the locations of gages with rainfall in the last 24 hours. But you can also select other time periods in the sidebar. The storm dropped water during most of the week. So I selected “7 Days.” I also selected “All Gages” to see the varying amounts of rainfall across the region.

Then I clicked “Watersheds,” and “Channels.” Automagically, 7-day rainfall totals appear over a map that lets you see which watersheds the rain fell in. That determines how it will work its way downstream to the Gulf.

From Harris County Flood Warning System on 1/27/24 at 6:18 am.

On the low side, values ranged from 4″ to 6″ south of Lake Houston. On the high side, they ranged from 9″ to almost 11″ north and west of Lake Conroe. Such variation is common.

Step Two: Find the Duration and Distribution of the Rainfall

When you click on any gage location, a “For more information” box pops up. Click the link to see the distribution and duration of rainfall.

The gage at the San Jacinto West Fork and US59 received 5″ during five days. If a giant peak on one day outweighed all others, you might want to investigate that particular day further. But in this case, most days were within a half inch of each other.

Now, you’re ready to find how that compares to other storms.

Step Three: Compare Recorded Totals to Precipitation Frequency Estimates

Next, compare recorded rainfall to expected rainfalls of different intensities and durations.

Most hydrologists currently use precipitation frequency estimates called “Atlas 14.” NOAA determines them.

To find the estimates for your area, enter your address here. You should see a table like the one below although your numbers may vary slightly depending on where you live.

This is where some judgment comes in.

Determine the “best fit” between your observations and NOAA’s estimates.

So, I started by looking across the seven-day row and highlighted the first box. It showed 5.76 inches. The smaller numbers in parentheses indicate possible variation due to uncertainty. Almost all the lower numbers fell within this range.

At the high end of the observed rainfall totals, I highlighted the 10.4 inch box as the most representative. Again, all of the observed totals north and west of Lake Conroe fell into the range in parentheses.

Atlas-14 rainfall probability statistics for the Humble/Kingwood area.

Looking up to the top of the table, you can see that the highlighted boxes correspond to the volume of rain you could expect once every year to five-years. Meteorologists also refer to these as “100% and 20% annual-chance” storms.

If you live elsewhere on the map, you might find your area received a 50% annual-chance storm.

Rainfall Chances Do Not Automatically Translate into Flood Chances

For the record, the flood at the West Fork and US59 this morning peaked at 53.71 feet. That’s three feet LESS than a 10-year flood at this location.

From NWS at 6 am Saturday Jan. 27, 2024

So, in this case, the flood level was generally consistent with a 5-year rainfall upstream. But that’s not always the case.

Many people assume that a rainfall recurrence interval of 1- to 5 years automatically translates into the same probabilities for flooding. It doesn’t.

First, for large watersheds, such as the San Jacinto, rain can vary drastically. Variation upstream will determine how high the resulting water surface elevations are at various points downstream when peaks arrive.

Also understand that annual exceedance probabilities for floods incorporate many more variables than rainfall probabilities. For instance:

  • Landscape/Slope – Is it flat or hilly? Will water be bottlenecked or does it have room to spread out?
  • Degree of development – Are you surrounded by farms or do you live in an urban area which produces more runoff faster?
  • Soil type – More water infiltrates into sandy soils than clay.

Regardless, engineers still consider rainfall probabilities.

How Engineers Use Rainfall Estimates

Why are rainfall estimates important? Engineers must design drainage and infrastructure to handle extreme rainfalls.

For instance, most storm sewers are designed to handle the type of rain you can expect every year or two. When you see water ponding in streets or underpasses, it’s because the storm sewers can’t carry the water away fast enough.

Houston’s recently upgraded infrastructure design standards aim to keep structures safe in a 100-year event. It matters not whether the rain happens in five minutes or 60-days.

Engineers use these estimates when determining the elevation of homes, setbacks from a river, the size of stormwater detention basins and more.

When you see flooding of streets or neighborhoods, it’s generally a sign that:

  • Rainfall exceeded the design standard
  • Something changed, for instance, a sewer was blocked, sediment has clogged a drainage ditch, etc.
  • Someone miscalculated or cut corners during design and construction
  • Infrastructure was designed to old (lower) rainfall probability standards.
Last night, before the West Fork (upper left) peaked, water started flowing across Hamblen Road, cutting off some residents in North Shore.

Experts base the probability of extreme future events on the frequency of extremely rare past events using a branch of mathematics called extreme value analysis.

It’s important to understand that rainfall probability estimates change periodically – especially after major storms, such as Tropical Storm Allison or Hurricane Harvey. Meteorologists acquire additional data on extreme storms from these events.

All rainfall probability estimates represent best guesses given knowledge at a point in time.

NOAA is already working on Atlas-15 estimates. Atlas 15 will take climate change estimates into account for the first time.

Going forward, NOAA will compile new precipitation-frequency estimates every 10-years.

Posted by Bob Rehak on 1/27/24

2342 Days since Hurricane Harvey

Flood Crests Closer to Lake Houston

Friday, 1/26/24 – Flood crests moved closer to Lake Houston this morning. Crests in the upper Lake Houston Area should happen today and tomorrow. Here is today’s lake and river report based on information provided by Harris County Meteorologist Jeff Lindner.

While rain chances will be high today, actual amounts will be low – generally less than .50 of an inch and more likely less than .25 of an inch. This amount of rainfall will not cause any additional flooding over the region. Drier and cooler conditions will filter into the area over the weekend.

Run-off from the rains this week continues with several rivers flooding, but we are starting to see some crests and slow improvement as flood waves move downstream.

Lake Conroe

The level in Lake Conroe started decreasing this morning. So did the SJRA’s release rate by 3,000 cubic feet per second. It is now down to 16,500 CFS at noon.

Spring Creek: 

Spring creek has crested and fallen rapidly in the headwaters to SH 249 overnight. The middle and lower portion of the creek is cresting and will fall today. Minor flooding along the creek will subside.

Upper Cypress Creek: 

Run-off from Waller County has finally reached upper Cypress Creek with flooding now in progress at Sharp Road. The creek is slowly rising and will crest later today, but remain above bankfull into tonight. Flooding of portions of Sharp Rd is ongoing and will continue. No flooding is expected downstream of Katy Hockley where the capacity of the creek increases.

West Fork of the San Jacinto River (Lake Conroe to SH 99)

The river has crested overnight and is starting to fall, but remains above major flood levels with widespread impacts ongoing. Water levels will be decreasing slowly today and then faster into the weekend.

West Fork of the San Jacinto River (US 59 to Lake Houston):

The river began a secondary rise overnight and it is continuing this morning with a long duration crest later today into Saturday around 52.5ft.

Jeff Lindner

The US 59 turn arounds under the US 59 bridge crossing are under water and will be flooded well into the weekend.

Several streets on the north bank of the river are flooded including Lakeshore, Northshore, River Bend, and Lake Point. The majority of the flooding will occur south of Hamblen Rd…although a few location north of Hamblen could see high water. The few structures in this area are elevated and are cut-off into the weekend as water levels remain elevated.

Large portions of the Kingwood Golf course are/will be flooded. At these levels back water will also begin to effect tributary drainage channels into the river and higher than normal water is likely along these tributaries. No flooding of homes is expected in Kingwood. See inundation map below.

West Fork inundation map in Humble/Kingwood area as of 11am 1/26/24

Note: There is about a 6.0 ft difference in the water surface elevation between US 59 and West Lake Houston Pkwy. We are NOT going to get to 52.5ft at W Lake Houston Pkwy…we will see levels between 46.0-47.0 ft at crest.  

East Fork of the San Jacinto River:    

The river rose 6-8 ft overnight from Plum Grove to New Caney with widespread low land flooding along the river in progress from above Plum Grove to Lake Houston.

East Fork at FM1485. As of 11 am, the river was still above 68 feet.

FM 1485 west of the river bridge is now flooded and will be impassable for an extended period of time. Additionally, some roads on the west side of the river just downstream of FM 1485 will be flooded and elevated structures cut-off. Elevated structures downstream on the east river bank off River Terrace Rd will be cut-off. The river is forecasted to remain well above flood stage through the weekend.

Here are two inundation maps from Harris County’s Flood Warning System as of 11 am on 1/26/24.

If you live in an area not shown here, go to the interactive map, click on “inundation” in the left control panel, and scroll the map to your location.

Lake Houston: 

High flows are moving through Lake Houston…the total inflow into the Lake from all combined run-off sources this morning was 67,580 cfs with a total discharge of 50,878 over the spillway and through the tainter gates.

Since the inflow is still greater than the outflow the lake level will still rise some today. Water levels throughout the lake are elevated and above the bulkheads and docks at several locations.

Lower San Jacinto River below Lake Houston: 

The river is rising with minor flooding now ongoing at Sheldon (HWY 90). Minor to moderate flooding is forecasted along the river from below Lake Houston to Galveston Bay.

Low lying areas of Sheldon, Banana Bend, Highland Shores, and Rio Villa will experience flooding of roadways and may become cut-off (Rio Villa). Higher than normal flows will impact vessel traffic around I-10 and vessels should be properly secured for a period of prolonged increased flows and high water levels.

The river will peak between 6.0-8.0 ft at Rio Villa Saturday. This area should be prepared for rising water today and potentially being cut-off as the water overtops Wallisville Rd.

Trinity River: 

Major flooding is forecasted from below Lake Livingston to Goodrich and near Liberty. Some homes below the lake will be flooded. Several subdivisions will be cut-off around Liberty and at the current forecasted levels…widespread extensive flooding over portions of Liberty County near the river and its tributaries can be expected.

For Current Information at Any Time

Current water levels and inundation can be found at www.harriscountyfws.org

River forecast can be found at National Weather Service Advanced Hydrologic Prediction Service

Posted by Bob Rehak on 1/25/2024 based on information from Jeff Lindner

2341 Days since Hurricane Harvey