Riverstone - Brazos River Update 4pm 8/28/2017

EXPLAINING THE FLOODING THREATS TO THE COMMUNITY

The Brazos River at the Richmond Gauge is at 47.04 feet as of 1:15pm Aug 28. The National Weather Service (NWS) is currently predicting a crest at 59 feet on Tuesday afternoon/evening.   

IMPORTANT: 59 FEET IS A MEASURE OF THE DEPTH OF THE RIVER AT THE RICHMOND BRIDGE. IT IS NOT AN ELEVATION IN RIVERSTONE. THE RIVER AT THIS LEVEL WILL BE 4-10 FEET ABOVE THE NATURAL GROUND INSIDE THE LEVEES IN RIVERSTONE.

The NWS is also predicting an additional 15 inches of rain over the next 3 days.

The levee and drainage system is fully operational and functional at this time. But this event will exceed the design of the system.

Why an evacuation now? The concern is that while the system is functioning now, the amount of water predicted in the river and the amount of rain predicted to fall inside the levees in the next three days have the potential to overwhelm the system. If that were to happen during the crest in the river, there would be no time to evacuate the residents.

We face two different threats at this time, either of which have the potential to cause flooding: 

1. Water from the Brazos River could get into the community. This could happen one of two ways:
   • The river could rise to a level higher than the tops of the levees (“overtopping”). The forecast for the Brazos River has it cresting just below the tops of the levees.   The current river prediction means we should not be overtopped, that elevation is just a model, and the actual elevation of the river will not be known until after it reaches its peak and begins to go down.  
   • The levees could fail (“a breach”). With this much water against an earthen levee, there is a potential that the levee fails allowing the water to come into the community--even at a level below the top of the levee.
2. Rainwater that falls in Riverstone can’t be pumped out fast enough.
   • When the river is as high as it is now, the lakes and channels cannot drain directly into the river. Our system has two pump stations that pump the water over the levee into the Brazos River.
   • The lakes and drainage system can only handle so much water before becoming overwhelmed. If the rain continues to fall at the rates we have seen, the lakes and channels will begin to get out of their banks.
   • Initially, that rainwater will fill the streets and roads in Riverstone, making them impassible within the community. If enough rain falls in a short period of time, the water could eventually reach homes.  

We have no way of knowing how much rain will fall in the coming days, or how high the river will ultimately get, or how long it will remain at that level. Therefore, at this time, we don’t know for certain whether or not Riverstone will experience flooding.  But given the rainfall and river predictions that are currently being made, this will be the most significant flooding threat the District has ever faced.

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