1.   FLOODS/FLASHFLOODS

 GENERAL CHARACTERISTICS 

Historically, floods are and continue to be one of the most destructive and costly natural hazards facing Polk County, constituting 90% of the disaster damage in the County.  Very few areas in Polk County are completely free from the threat of floods. 

Floods are natural and recurring events.  They become a hazard when people compete for the use of floodplains.  The natural function of a floodplain is to carry away excess water in time of flood. Failure to recognize this function has led to rapid and haphazard development in floodplains and consequent increases in flood hazards.  However, Polk County has been actively involved in floodplain management and is a participant in the National Flood Insurance Program (NFIP).  In 1990, severe rains in the Dallas area and in the upper Trinity River Water shed produced record floods in the lower Trinity River Basin.  These floods convinced County officials of the need for flood insurance to protect people living in flood prone areas and that managing the floodplain is an absolute necessity.  

Late fall and early spring floods caused by supercell thunderstorms are common in the Polk County area.  Summer floods are uncommon events, except for those associated with hurricanes and tropical storms that may occur in summer and autumn. On the basis of present knowledge, the size, time and place of floods cannot be predicted more than a few hours in advance. 

TYPES OF FLOODS COMMON TO POLK COUNTY 

Flash Floods: A flash flood generally results from a torrential rain or "cloudburst" on a relatively small drainage area.  Runoff from these intense rainfalls result in high flood waters that can destroy roads, bridges, homes, buildings and other community developments.  Discharges quickly reach a maximum and diminish almost as rapidly.  Flash floods are a potential source of destruction and a threat to public safety in areas where the terrain is steep or hilly, surface runoff rates are high, streams flow in narrow creek beds and gullies or severe thunderstorms stall over an area. 

Due to the rapid growth and development many areas in the county that have never experienced flooding and do not have a history of flooding are now experiencing flashflood problems.  New housing projects, roads, commercial buildings and increased land usage, including clear cutting forestlands have substantially increased the potential for flooding.  Few areas of the County are free from the effects of flashfloods, below is a listing of these areas. 

 Riverine Floods: Riverine floods are caused by precipitation over large areas and differ from flash floods in their extent and duration.  Riverine floods take place in river systems whose tributaries may drain large geographic areas and encompass many independent river basins.  Floods in large river systems may continue for periods ranging from a few hours to many days or even weeks.  Flood flows in large river systems are influenced primarily by variations in the intensity, amount, and distribution of precipitation. The condition of the ground, amount of soil moisture, seasonal variations in vegetation and imperviousness due to urbanization directly affects flood runoff.   

Floodplain:  The lowland and relatively flat areas adjoining the Trinity River, Lake Livingston, the Neches River and along the many creeks throughout the county.  At a minimum, that area is subject to a one percent or greater chance of flooding in any given year.  (See attached floodplain map). 

Areas in Polk County that are affected by the Trinity River and that are subject to Riverine flooding are as follows: 

1.      Big Thicket Lake Estates: 

In October 1994, severe flooding in Polk County washed out the existing road and dam that crossed Big Foot Lake.  This dam provided the residents of this subdivision the only means of ingress and egress for the East Side of the lake and Mill Creek.  The breach in the entrance road was by-passed with an emergency road that has washed out on numerous occasions since the 1994 flood.  About eight hundred (800) residents are left without access to their homes on the East Side of the subdivision.  This area has 350 permanent residents that live on the Polk County side of the subdivision. 

On March 13, 1997 the temporary roadway was washed out and an accident involving a NGL 10’ pipeline forced County authorities to evacuate the entire subdivision.  With this turn of events Judge Thompson asked the Governor to declare this event a disaster and a grant through TDHCA was applied for and granted.  

This subdivision has a history of flashfloods washing out dam, culverts, and roadways.  Historically the single entrance to this area has washed out over 12 time since 1986.  This subdivision has been evacuated twice since March ,1996.  There is a major effort to build an all weather bridge and roadway into Big Thicket, this should mitigate the problem.           

2.      Taylor Lake Estates 

Located in the Southern end of Polk County adjacent to the Trinity River.  The entire subdivision constructed within the 100 year floodplain.  A 2.8 mile levee was built around the area to protect homes from flooding.  This area does flood during extremely heavy rains, the roads flood cutting off all ingress and egress.  The levee system provided ample protection to the subdivision, however, the worse possible scenario (i.e. heavy rains in the Dallas area and two weeks later torrential local rains) would cause disastrous flooding, causing the subdivision to become a fishbowl. This area has 250 permanent residents. 

The Army Corps of Engineers conducted a reconnaissance study on the Lower Trinity River basin that was initiated April 1, 1991.  The study area consists of the Trinity River basin from the City of Dallas to Trinity Bay.  The study was to investigate various structural and non-structural alternatives designed to alleviate and /or prevent flooding. Taylor Lake Estates was identified as the program with the greatest benefit/cost ratio. 

3.      Holiday Lake Estates 

Located on FM 2665 about four (4) miles East of Goodrich.  The subdivision has 450 permanent residents and of that number approximately 150 live within the 100-year floodplain.   The subdivision is adjacent to the Trinity River and has four (4) man made lakes that are fed by Sally Creek.  Lake Londa Lynn is .0992 sq. mile in area with a dam that spans approximately 700 feet.  Holiday Lake is the smallest of the lakes with a total area of  .0249 sq. mile and Gerlach Lake with a total area of  .1216 sq. mile.  During heavy rains the two (2) roads that control all ingress and egress from this subdivision are flooded and are impassable.  

Most of the homes along River Road adjacent to the Trinity River are located within the 100-year floodplain.  Several homes adjacent to the Trinity River are located on elevated land, however due to years of river erosion they are now in eminent danger of being destroyed by river erosion. 

Notice to evacuate is normally given to this area once the release at the Livingston Dam reaches 75,000 cfs.  Flood stage is determined from the gage at the US 59 bridge, 36 feet at gage height or 47,510 cfs. 

4.      Goodrich Area 

Siesta Country, Hoot Owl Hollow, River Lake Estates, FM 2969 and FM 1988 at Long King Creek are all located within the 100-year floodplain.  Approximately 400 permanent residents live in this area and are in danger of both riverine and flashflood or a combination of both.  In October 1994, there was one (1) fatality on FM 2969 from drowning.  The roads flood and residents are cut off without any means of ingress or egress.  It is very difficult to determine when to issue voluntary evacuation notices, local rains play a key role in this determination. 

Both Siesta Country and Hoot Owl Hollow were part of the 404 HMGP property acquisition in 1994 – 1998.  Only parts of the properties were purchased.  Several permanent residents still live in both of these areas.    

Approximately 1,400 homes are located within these areas.  Many of these homes have been elevated above the known Base Flood Elevation (BFE). However flood hazard boundary maps for this region are from a study preformed in December 13, 1977,  and were manually updated by changing the date to March 1, 1991.   The growth in Polk County and in the Trinity River Watershed in the Dallas area has greatly affected the floodplain, Many areas that have never had a history of flooding are now experiencing flood problems.  Until a new study is done we will continuously have problems identifying the floodplain and establishing effective BFEs. 

Most all areas in Polk County are subject to Flashfloods, many times, very little or no warning is available.  Due to heavy land usage, new construction, clear cutting and commercial use it is very difficult to provide adequate warning and develop effective warning systems during flash floods. 

MITIGATION MEASURES: 

The key actions for effective reduction of flood losses lies in appropriate planning for regulating the use of flood prone land.  At one time, the trend was toward structural flood control. For example, the building of dikes, dams and levees, which was found to be costly and sometimes not as effective as other actions. 

The current trend is to clear high-risk areas through voluntary acquisition programs and more strongly enforce floodplain management. This concept includes the acquisition of property, adoption of proper floodplain zoning regulations, land use planning and promotion of the sale of flood insurance.  The National Flood Insurance Act requires flood-prone communities to take corrective and preventive measures to minimize the effects of flooding. 

Citizens look to their community and to public service agencies within the community, to prevent loss of life and unnecessary destruction of property. Some of the minimal expectations are a severe weather early warning system; adequate shelter facilities and evacuation assistance when necessary.  Also, community participation in the National Flood Insurance Program, enforcement of an effective floodplain management program; a local office where base flood elevation levels and information as to the susceptibly for flooding can be obtained; and adoption and enforcement of building codes that ensure safe, survivable structures. 

Polk County has developed a strong floodplain management program and has gone to great lengths to ensure that persons building or developing floodplain areas are properly permitted and that stringent guidelines are adhered to.  

Most Notable Floods in Polk County 1989 – 1998

May 3 – June 15, 1989                     Heavy local rains caused severe flashflood problems

                                                            throughout Polk County.

* May 10 – June 12, 1990                Heavy rains in the Dallas area caused severe

                                                            flooding all along the Lower Trinity River Basin

                                                            Lake Livingston Dam recorded record releases.

 * December 18 – 31, 1991              Heavy local rains coupled with severe riverine flooding caused                                                                 severe flooding along the Lower Trinity River Basin. 

 * October 15 – 19, 1994                 Heavy local rains caused severe flash and riverine flooding all along the water shed of Kickapoo, Rocky, Sandy, Long King, and Menard Creeks.  This flooding produced record releases at the Lake Livingston Dam Site.  Flooding affected hundreds of homes throughout Polk County.  Nine (9) bridges were washed out along with roads and culverts. 

* November 13 – 16, 1998              Heavy local rains coupled with severe riverine flooding caused severe flooding along the Lower

                                                            Trinity River Basin causing severe damage to county roads and bridges. Washing a number of bridges and culverts out. A number of homes were flooded. 

April 3 – 4, 1999                               Heavy rains caused record flooding along Choate, Long King and Menard Creeks causing severe damage to county roads and bridges. Washing out three (3) bridges and several culverts. Approx. 50 businesses were closed or destroyed and several hundred homes were flooded, with about 30 destroyed. Damaged was severe, however it was not enough for a Presidential declaration. This was an SBA. 

*      Presidential Declaration  

Flooding will continue to be the biggest threat to the citizens of Polk County.  The County Judge and Commissioners continue to strive to reduce losses from flooding by appropriate planning, regulation of flood prone land and promotion of the purchase of Floodplain Insurance.  Polk County has and will continue to enforce a rigid floodplain management program.  

This Homepage was prepared by Kenneth F. Hambrick, Polk County Coordinator. Contact at E-Mail address: webmaster@pcoem.org  for additional information about our program. The information contained in this Homepage is considered public domain and the Office of Emergency Management encourages interested persons to utilize any portions of it that might be of educational benefit or enhance their local programs.

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