The City of Simonton is located on the Brazos River floodplain, approximately 25 miles west of Houston, Texas. It was established in 1957 and incorporated in 1979. Although a "new" city as cities go, Simonton has a history going back to the 1850s.In 1997 it consisted of 195 homes with an assessed value of approximately $13.5 million dollars. Almost all of the City is located within the Federal Emergency Management Agency (FEMA) 100 year floodplain of the Brazos River.
Floods along the Brazos River in October, 1991 and December, 1995 caused serious damage in the Simonton area; in particular in the Valley Lodge subdivision. Approximately 100 homes were flooded in 1991 and 125 in 1994. The latter flood caused approximately $2.5 million dollars damage. Flood insurance claims for the subdivision since 1978 total approximately $4.5 million dollars. Clearly Simonton has a problem!
A series of flood hazard maps from Environmental Systems Research Institute, Inc. are used with their kind permission.
The Bend of the Brazos is marked by a rectangle on the images that follow. Note the distribution of the 100 year flood plain (the darker green). Can you spot a problem waiting to happen?
The Brazos River flows from top to bottom on this image. Simonton, Texas is about 1 mile east of the outlined Bend of the Brazos. Note the cresentric bodies of water near the main channel of the Brazos. How do you think they may have formed?
The width of land in the neck of the Bend of the Brazos is narrowing with time and eventually the two channels will intersect. An oxbow lake (above) represents a former active meander bend. The scar of a former oxbox lake (which has been filled in with sediment) occurs in the lower part of the image above.
The Valley Lodge subdivision lies in the neck of the Bend of the Brazos River.
If you lived in Valley Lodge wouldn't you want to know how long it might take for the two channels to intersect?
Flooding along the Brazos River Near Simonton, Texas
The maximum annual discharge of the Brazos near Simonton, Texas has varied from about 125,000 cfm to 10,000 cfm in the past 70; a considerable range which makes living in the Brazos flood plain a risky business.
The maximum annual discharge data are from approximately 12 miles south of Simonton at Richmond, Texas. There were about 9 events that exceeded 90,000 cubic feet per minute. These events caused major problems for the residents who live in the flood plain of the Brazos.
Exercise 1 - Flooding Along The Brazos River Near Simonton
Evolution of a Meandering River
Note that there is another hazard facing the residents, especially those that live in the Valley Lodge subdivision. Even without flooding, the Brazos River is in the process of changing is channel over time. Think about the velocity when the water column is in a straight channel. At the boundary between the water and the channel perimeter the velocity is reduced by friction. Within the water column, away from contact with the channel bottom and sides and with the atmosphere, the velocity is about the same. Ideally, a cross-section of the channel would be symmetrical.
Now think about a channel with bends - a meandering channel. On the outside of the bend the velocity is higher than on the inside. The channel is eroding on the outside of a meander bend (the cut-bank ) and depositing material on the inside of a meander bend (point bar formation). With time, therefore, the channel will migrate across the floodplain.
Watch the following animation and remember that the residents of Valley Lodge live in the narrowing neck of the meander. Evolution Of A Meandering River. Remember that flooding will exacerbate the problems these residents face.
Now, watch the Evolution of the Brazos Bend at Simonton, Texas from 1958 to 2000 with a projection on into the future.
Exercise 2 - Land Erosion Along the Brazos River Near Simonton
As a review of the situations facing the Simonton, Texas, residents, you may wish to view the A Power Point Presentation