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Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 37, No. 7, March 1995. Pages 9-9.

Abstract: The October 1994 Record Previous HitFloodNext Hit, San Jacinto River Drainage Basin, Southeast Texas


Rufus J. LeBlanc, Sr.
Environmental Geology Consultant

The San Jacinto River drains a Quaternary and Pliocene terrain ranging in elevation from 425 feet to sea level. The river basin forms the homesites for hundreds of HGS members in communities north and east of Houston, Texas. During three days in October, 1994, up to 30 inches of rain fell within the river basin. The river's Previous HitfloodNext Hit plains were rapidly inundated. Homes and roads were destroyed or badly damaged. Many lives were lost. Up to seven feet of sand, in the form of huge sand waves, was deposited on the Previous HitfloodNext Hit plain south of Lake Houston During the height of the Previous HitfloodNext Hit, segments of several petroleum products pipelines crossing the Previous HitfloodNext Hit plain were ruptured south of the Lake Houston spillway.

There were geologic reasons for the erosion and the pipeline ruptures that occurred during the Previous HitfloodNext Hit. Water flowed over the Lake Houston spillway at ten miles per hour and down the 4.5 miles of sinuous river bed towards the Banana Bend area. The volume of water coming down the spillway and entering the river channel was 356,000 cubic feet of water per second. When this wall of water reached the large meanders in the Banana Bend and Rio Villa subdivision areas, the main path of the Previous HitfloodNext Hit waters left the thalweg of the channel and flowed straight south across the river levees. Three documented avulsions occurred at the levee cuts across the sand-rich Previous HitfloodNext Hit plain. Point bar sands from the main river channel were rapidly eroded and deposited as huge sand waves along the Previous Hitflood'sNext Hit path.

A major avulsion at the Rio Villa subdivision isolated the community and ruptured several pipelines. The leaking hydrocarbons floated southward for 2.2 miles to the Whites Lake area near I-10 where they concentrated in an eddy and ignited. The fire subsequently spread north along the plume of floating hydrocarbons to the source at the rupture.

There was not a single pipeline rupture along the normal meandering course of the San Jacinto River. Instead, the ruptures took place at a point where the river attempted to cut a new channel into the Previous HitfloodNext Hit plain, following normal geologic processes of a meandering river in Previous HitfloodTop stage.

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