COMMENT OF THE DAY: FURTHER READING INTO YOUR HOUSTON FLOOD AND FIRE CHANCES “Every home is susceptible to flooding. There are not ANY non-flood areas. There are only homes that are more likely to flood and homes that are less likely to flood. The likelihood is expressed, on flood maps, by the single-year probability of being flooded (with some other factors). This does not properly describe the likelihood of being flooded during the course of a longer time period — of, say, a 30-year mortgage. Homes eligible for NFIP preferred flood rates can have up to just less than a 1 percent chance of flooding annually. These ‘preferred areas’ are what the public thinks of, euphemistically, as non-flood areas. Assuming a .009 probability (just less than 1 percent), a home has a 20 percent chance of flooding, at least once, over the course of a 30-year mortgage (look up binomial probability). An alternative way to think about it is that 1 in 5 homes, in preferred flood zones, will flood over the course of a 30-year mortgage. [In that case,] you are actually more likely to experience a flood than a house fire in a ‘preferred flood area.'” [Jardinero1, commenting on Where Houston Floods Outside the Flood Zones] Image of recent flood map revisions: FEMA RiskMap6
From some of the same folks who brought you those fun-with-worst-case-scenarios hurricane flood maps earlier this year — Neena Satija and Kiah Collier of the Texas Tribune, and Al Shaw of ProPublica — comes a fresh set of animated maps of a few of Harris County’s most flooded and floodable places, along with a bit of investigation into how they got that way (and whether that might change any time soon). The new illustrated presentation shows off the spread of properties that took a dip during some of Harris County’s last few citywide submersion events (flooded properties from Tax Day 2016 are shown in yellow above, along with the Memorial Day 2015 flooded properties in orange).
Texas A&M Galveston researcher Sam Brody tells the authors that “more people die here than anywhere else from floods. More property per capita is lost here. And the problem’s getting worse.” In sorting through some of the whos, whats, and hows of Harris County’s flood infrastructure and chronically soggy residents, the article juxtaposes the recent flood damage data with the likes of FEMA-mapped 100- and 500-year flood zones (shown above), a visual tally of the land area developed last decade, and a view of what’s left of Houston’s coastal prairie (as of 2010):
The areas in red above mark some of the new additions to the legally-gotta-buy-flood-insurance zones on FEMA’s recently revised flood maps. The agency’s interactive online viewer lets you mix-and-match a few data sets for Harris County (as well as Galveston, Fort Bend, and Wharton), compare the old mapped flood zone boundaries to proposed new ones, or look only at what would change — a FEMA spokesperson told Houston Public Media that about 8,000 properties have been added to the list in Harris County, while only about 400 were dropped.
Those acid-green highlights are areas that have been removed from the special flood hazard zone by the updated map (while blue shows areas that have just changed floodplain classification some other way. Bits of brown and yellow in other areas of the map show places added or removed (respectively) from the floodway. The updates above to the mandatory flood insurance zone (legally called the Special Flood Hazard Area) are set to go into effect in January, as shown above.Buffalo Bayou and its tributaries are pretty marked up:
Residents of the Rio Brazos area near Cumings Rd. north of Rosharon are being advised as of this afternoon to boil their tap water until further notice, while the Fort Bend County Fresh Water Supply District 2 sorts out possible problems stemming from a flood-related loss of water pressure in the network. (The map included here has been added to the Fort Bend County emergency office’s Facebook page following a brief online outpouring of confusion as to what neighborhoods the warning was actually targeting.)
Meanwhile, TXDOT is still listing dozens of miles of roadways as covered by to high water as of this morning, with more closures expected as Brazos floodwaters drain southwest toward Angleton and Freeport. Here’s Brazoria County’s latest worst case scenario potential floodmap, with the county’s mandatory evacuation zones now stretching across more than 15 miles from roughly Brazos Bend State Park to the outskirts of Angleton:
COMMENT OF THE DAY: WHY FLOOD CONTROL ENTHUSIASTS KEEP EYEING PREVIOUSLY PAVED LOTS “This is a standard practice: to elevate [existing] commercial properties so they will drain off the property. It is very easy to do. The concern is that the city of Houston does not require new properties on old lots to detain water on the lot. . . . Elevated commercial properties that do not mitigate acre-foot-for-acre-foot will lead to water running off and flooding adjacent properties. It is a simple concept, but developer propaganda is strong. The most common myth promulgated by the developers is that if something was already concrete then a new property need not mitigate run-off. The fact is, any time a new development is built that does not mitigate run-off, it will force water onto its neighbor. [Flooding, commenting on Former Fiesta Site Preps for Teardown as Heights Dry Zone Petitioners Circle] Illustration: Lulu
TxDOT has been doing some circling around over the thoroughly soaked Brazos River valley this week grabbing a few snapshots, including some taken yesterday morning as 31 East and Central Texas counties picked up flood-related disaster declarations from the governor’s office. Running north-to-south (right-to-left) under the murky waters shown above is FM 723 in Rosenberg, TX; you can spot the bridge rising up to cross the river’s normal channel on the left side of the photo, while SH 36 stretches away to the northwest.
Flash- and non-flash flood warnings are in effect around the region through at least Friday night, depending on how intense the rest of this week’s predicted downpours turn out to be. Meanwhile, the already-feet-past-the-previous-record flood gauge at nearby Richmond, TX, is still creeping upward this morning toward 55 ft.:
The footage above captures Ed Nelson’s high-water trek last Monday through an overflowing detention basin at the corner of Bob White Dr. and Reamer St. just north of Brays Bayou. Nelson narrates his soggy expedition through the basin (which sits at the south end of the Robindell and Braes Timbers neighborhoods, between Hillcroft Ave. and Fondren Rd.) as he attempts to document different flows of water into and out of the pond; he ultimately claims that water is flowing into the detention pond from Brays, and moving from there into the floodway easement running behind nearby houses on Reamer.
Nelson and other neighbors claim that the surrounding area did not flood prior to the detention basin’s completion in 2008, and that the detention pond was intended to collect water from the surrounding neighborhood and prevent it from flowing too quickly into Brays bayou — whereas during the Tax Day and Memorial Day floods, the basin purportedly collected water from the bayou and channeled it into the neighborhood, causing houses to flood that neighbors believe might not have otherwise.
A water-watching reader sends some south-facing photos from yesterday evening (right) and last October, comparing views over the fenceline of the 400-ft.-wide diversion channel at the northern edge of the Addicks reservoir. The channel picks up most of the flow from Langham and Horsepen creeks where they join up as they flow south into Addicks. The 400-ft.-wide floodway was dug in the 1980s; the flow usually lurks down in the narrow channel seen in the shot on the left.
The scene above is less than a mile east of Bear Creek Village, where water is now moseying into neighborhoods from the western edge of the reservoir (and washing some wildife and livestock around). The Army Corps of Engineers has been releasing water from both Addicks and Barker dams to minimize the pooling (and relieve stress on the dam structures themselves) — but those releases have to be done slowly enough to avoid causing additional flooding downstream along Buffalo Bayou. Meanwhile, water is still flowing into the reservoirs from western watersheds; the measured levels behind the 2 dams topped all previous water level records and normally allowed pooling limits in the reservoir by Tuesday, and has been rising since. Here’s a shot of water gushing out through some of the gates of the Barker dam this afternoon: