|
|
 |
|
|
Buffalo Bayou & Lower White Oak Bayou Federal Flood Damage Reduction and Ecosystem Restoration Study
Revisiting Hurricane Ike: Report on Buffalo and Lower White Oak Bayou Study Area
March 26, 2009
This brief report is primarily focused on the Buffalo Bayou and lower White Oak Bayou study area and is not intended to cover the entire area impacted by Hurricane Ike.
> See more information on Hurricane Ike at National Weather Service Houston/Galveston
When Hurricane Ike made landfall at Galveston Island on Saturday, September 13, 2008, it had a devastating impact throughout southeast Texas. The 110 mph Category 2 hurricane tracked north-northwest through Harris County producing a devastating storm surge and two separate flooding events. Sustained winds of 60 to 70 mph and wind gusts of 80 to 90 mph were measured, and widespread flood and wind damage occurred throughout the county.
Storm Surge
Hurricane Ike produced the highest storm surge along the upper Texas coast since 1915. Specifically in the study area along Buffalo Bayou, out-of-bank flooding due to storm surge occurred downstream of Downtown Houston by late Friday afternoon, September 12, and well before the onset of the outer rain bands of the hurricane. Water level rises in Buffalo Bayou were noted up to Shepherd Drive. However, once it started raining in Harris County, the storm surge did not prevent the drainage of stormwater runoff from inland locations.
Rainfall Event #1 (Friday night to Saturday – September 12 and 13, 2008)
Two rainfall events were tracked. During the first rainfall event, widespread excessive rainfall occurred along the track of Hurricane Ike as it made landfall. The 24-hour rainfall totals averaged 6 to 8 inches across Harris County in a 10-mile band from Friendswood to Downtown Houston and a 20-mile band from Downtown Houston to The Woodlands, between SH 249 and US 59. The rainfall frequency ranged from a 20% (5-year) to a 1% (100-year) event across Harris County.
In the study area, minor out-of-bank flooding from the rainfall occurred in the White Oak Bayou watershed downstream of Heights Boulevard and Buffalo Bayou watershed downstream of the 610 West Loop.
Rainfall Event #2 (Sunday, September 14, 2008)
The second rainfall event produced excessive rainfall from Katy to Kingwood and from Missouri City to the Sheldon Reservoir. Rainfall in this band averaged 2 to 4 inches with isolated amounts of 5 to 6 inches over the middle part of White Oak Bayou and an isolated area of rainfall of more than 8 inches in 3 hours [or a 1% (100-year) frequency] reported at White Oak Bayou and Ella Boulevard.
Because of complete saturation from the rains during the landfall of the hurricane, massive amounts of debris, and many bayous still swollen with stormwater from Hurricane Ike, the second rainfall event produced extensive flooding of bayous and area roadways. The rainfall frequency ranged from a 10% (10-year) to 1% (100-year) event mainly over White Oak and Buffalo Bayous and the San Jacinto River. In the study area, minor out-of-bank flooding occurred along Buffalo Bayou downstream of Shepherd Drive and White Oak Bayou downstream of Heights Boulevard.
Storm Rainfall Total
Gage networks maintained by the Harris County Office of Homeland Security & Emergency Management and the U.S. Geological Survey (USGS) indicate that overall storm totals averaged 10 to 13 inches with isolated amounts of 15 to 18 inches. This rainfall total is equivalent to between a 10% (10-year) and 1% (100-year) rainfall frequency across a large part of Harris County. In the study area, the Turning Basin area experienced heavy rainfall with up to a 1% (100-year) frequency and the majority of Buffalo Bayou experienced a rainfall frequency of 10% (10-year) or less. Based on available gage data, lower White Oak Bayou experienced rainfall from a 10% (10-year) to 1% (100-year) frequency.
House Flooding
Across the Houston/Galveston area, flooding of homes and businesses occurred from: (1) storm surge, (2) bayous overflowing their banks, (3) overland flow (water trying to reach the bayous but couldn’t), and (4) internal drainage (storm sewers and roadside ditches exceeding their capacities and holding large amounts of vegetative debris from the hurricane).
> See Harris County’s Floodplain Types
Based on the reported flooding information, approximately 1,300 houses and 200 apartment units were flooded by rainfall between September 12 and 14 in Harris County. Approximately 2,500 houses were flooded by storm surge in Harris County. In the study area, flooding was reported in 12 apartment units along lower White Oak Bayou. No reports were received of home or apartment flooding along Buffalo Bayou.
|
|
|
|
|
 |
|
|
|
Buffalo Bayou & Lower White Oak Bayou Federal Flood Damage Reduction and Ecosystem Restoration Study
|
|
|
