How Much Water Came from Where on the East Fork During Imelda ?
The San Jacinto East Fork watershed is immense. Many homes, vehicles, businesses and properties flooded along it during Imelda. Northeast Harris and East Montgomery counties, which contain the East Fork and its tributaries, received some of the heaviest rainfalls during that storm. So how much water came down them? And how did the peaks compare to Harvey?
East Fork Totals Computed by Harris County Flood Control
Jeff Lindner, Harris County Flood Control’s meteorologist computed the peak flows in cubic feet per second for ReduceFlooding.com.
He used the following gages. They are the closest to Kingwood and Huffman :
- Peach Creek at FM2090
- East Fork at FM1485
- Caney Creek at FM2090
The peak flows in cubic feet per second past these gages during Imelda were:
- East Fork = 34,600 cfs
- Peach Creek = 32,800 cfs
- Caney Creek = 9,230 cfs
- Total = 76,630 cfs
Numbers Probably Understate True Peaks
The peaks probably exceeded those farther downstream. But we have no way of telling by how much because those are the closest gages to Lake Houston.
Many storm drains and smaller tributaries without gages enter into the flow downstream of those gages. For instance, White Oak Creak, Taylor Gully, Red Gully, Mills Branch, Luce Bayou and more all enter into the East Fork before it reaches Lake Houston. And all of those carry a lot of runoff from developed areas, i.e., areas with a lot of impervious cover, meaning high runoff rates.
Net: Look at the 76,630 cubic feet per second as a minimum.
Comparison of Harvey to Imelda
How did the peaks on these three tributaries compare to Harvey? Consulting the SJRA’s peak flow map from Harvey, we can see that Harvey dumped much more rain:
- Caney Creek = 20,00 cfs
- Peach Creek = 31,300 cfs
- East Fork = 119,000 cfs
- Total = 170,000
So Harvey generated peak flows rates twice as high as Imelda. Only Peach Creek had a higher peak during Imelda than Harvey.
Importance of Looking Upstream when Comparing Storms
Remember, when comparing storms, it’s not just how much rain fell on you. It’s how much fell upstream from you. Rainfall patterns can produce dramatically different flooding patterns. During Imelda, while 20 inches of rain were falling on Patton Village, Lake Conroe received only two inches.
Posted by Bob Rehak on 10/17/2019, with thanks to Jeff Lindner and Harris County Flood Control
779 Days since Hurricane Harvey and 28 since Imelda
