The Rainfall Affect of Hurrican Rita on the Neches River

The hurricane moved inland almost parallelling the Neches River dumping a heavy rain 9/23/2005.  A 5-15 mile-wide swath of cumulative rain over 10 inches extended from near Beumont almost to Texarkana.  In response, the river rose 10 to 20 feet throughout much of its length.

Figure 1. shows the cumulative rainfall over the area from Doppler radar, the  Neches River Drainage basin, some relavant USGS  streamflow gauges, and the location of the major reservoirs within the basin.

Much of the lower Neches streamflow during normal periods comes from the upper Neches and from the Angelina River drainage system.  These are measured by the USGS streamflow gauges at Rockland and Alto respectively.  Prior to the huricane, these upriver areas were contributing water at only 130 and  20cubic feet per second rates (see Fig. 2.) to the downstream rate of 2600 cfs measured at Evandale, (prior to the storm beginning 9/23/2005).  The difference between the 2600cfs rate and the insignificant upstream rates was apparently mostly controlled discharge from Lake Sam Rayburn.

During the storm, large runnoff rates were measured at the two northerly streams feeding Lake Sam Rayburn (Fig. 3.)  Attoyac Bayou has a larger drainage area and contributed more runnoff than Ayish Bayou.

Downstream of the Angelina_Neches River junction  Town Bluff USGS stream gauge  measured rates increasing from 2800 to 24000cfs and the water rose over 20 feet.  Some of that storm surge was water arriving from drainage between Sam Rayburn reservoir and the Town Bluff station, and some was probably from Sam Rayburn and Steinhagen reservoirs themselves.

What is most interesting is the difference between the storm surge at Town Bluff and at the Evandale gauging station further downstream close to Beaumont.  See Fig. 4. for a comparison of those two streamflows.  Evandale received some runoff from the heavy rain directly but the flow rate never rose as sharply as the Town Bluff gauge.  Furthermore, high flow rates of 24000 cfs have not been seen yet a day and a half later at the downstream gauge.

Fig. 5. shows the area between the Town Bluff and the lower, Evandale gauging stations.  A very robust bottomland forest and swamp system exists between those stations and there are no man-made levees in that stretch.  Consequently those flood-prone forests and swamps periodically absorb much floodwater temporarily, alleviating downstream flooding.  Those woods and swamps are functioning  as very effective protection against severe river flooding in the Beaumont area.

Channelization and levee construction all along the Mississippi have had disastrous results downstream in that region.  Fortunately the Neches has not been channelized or leveed and the Neches woods and swamps are working towards lessening downstream flood damage.