Summary of the June 8 - 9 Flood over Brays Bayou and the Texas Medical Center

On the evening of Friday June 8, 2001, we began to watch the return of Tropical Storm Allison to the central Houston area. During the evening hours, beginning at 6:00 p.m., rainfall over Brays was steady until 11:00 p.m., but did not appear threatening, and there were small cells moving northward. After about 11:00 p.m, the northward bands stalled, began to move southward very slowly and began to grow in size and intensity. At 11:00 p.m., the Flood Alert System (FAS) predicted about 15,000 cubic feet per second (cfs) peak flow in Brays Bayou at Main St. From Midnight to 3 a.m, the Rice University rainfall gage unofficially recorded about 10.4 inches of rainfall. At 12:50 a.m., the Texas Medical Center was contacted and told of the imminent threat of flooding on Brays Bayou. At 1:56 a.m., just before Rice University's Internet Service Provider lost power, the Flood Alert System showed a predicted peak flow of 27,000 cfs. The final total rainfall at Rice University was 14.8 inches, with over 8.5 inches recorded in two hours. These rates of rainfall are some of the highest ever recorded over the Texas Medical Center.

Early Saturday morning June 9th, the Harris County Office of Emergency Management (HCOEM) stream level gage at Main St. showed a rapidly rising Brays Bayou. At 2:00 a.m., the HCOEM stream level gage at the Harris Gully outlet from TMC recorded 41.75 ft, or about 2.5 ft over the top of the wall above Harris Gully. High water marks in the area indicated that Brays rose to about 4.8 ft over the top of the Harris Gully Box culverts, near bankfull conditions. Maximum flood elevations around the TMC and Rice indicated as much as about 5 ft in Fannin and about 5 ft in Rice Boulevard, north of Rice Stadium. Due to the extremely high rate of rainfall for this event, the Southwest Freeway, under Hazard St., collected about 300 acre-feet (almost 100 million gallons) of flood water in a short period of time. The Southwest Freeway acted as a storage detention pond for flood water and is one reason that Rice and the Museum District were less severely impacted in this flood event. However, the enormous rainfall rates caused a large hydraulic gradient in the area and generated enormous overland flows to be directed towards the Texas Medical Center.

The Radar images or animation (1.7 MB) showed greater than 3 inches per hour being registered entirely within Loop 610 and areas east, including the University of Houston, along Brays Bayou. Table 1 indicates the average radar rainfall totals from the FAS for June 8 - 9, 2001, and clearly shows greater than 100 year rainfall totals for lower Brays (east of Main) and Mid-Brays (Main to Gessner). Upstream of Main Street, however, recorded 7.26 inches, between a 10- and 25-year storm. BayouCam pictures taken during Allison show the rapidly rising water levels after midnight.

In summary, this flood event of June 8 - 9, 2001 represents one of the most intense rainfalls to ever hit the Texas Medical Center. The event is clearly larger than the 1976 flood, since more than 5 ft of water stood in both Rice Blvd. and in Fannin Street. The incredible rates at which the rainfall and runoff occurred during this storm caused the water to exceed the height of the protection devices that were designed after the 1976 flood, and could not easily have been predicted in advance.