1. Presented by George Doubleday 1

2. What is The Woodlands Purpose of this Research Build and Calibrate Vflo TM model for The Woodlands Compare storms with different development scenarios 2

3.  Master planned community north of Houston, TX  Idealized by George Mitchell  Minimize impact of urbanization on hydrology 3

4.  Founded in 1974  Over 97,000 residents today  160 miles hike and bike trails  6,000 acres of green space Source: www.thewoodlands.com 4 I 45

5.  “LID enhances our ability to protect surface and ground water quality, maintain the integrity of aquatic living resources and ecosystems, and preserve the physical integrity of receiving streams.” Department of Natural Resources – Maryland  Utilize stormwater control practices throughout an urban watershed  Aim to preserve the pre-development hydrology while allowing for beneficial human use  “LID is a comprehensive technology-based approach to managing urban stormwater” DNR - Maryland 5

6.  Use hydrologic model, Vflo TM, to demonstrate The Woodlands as a premier example for stormwater management  Compare stormwater outflows from different development scenarios  Undeveloped  2006 Development  Highly Urbanized 6

7. GIS Pre-processing Input data into Vflo TM Calibrate to observed data 7

8.  Fully distributed physics-based hydrologic model  Variability of runoff controlling factors  Soil properties, land use/cover, elevation data  Infiltration calculated by Green and Ampt Equation  Runoff is routed from grid cell to grid cell  Finite Elements method  Kinematic Wave Analogy  Rainfall input can be rain gage data or radar rainfall 8 Developed by Vieux, Inc.

9. Land Use Soils DEM Vflo TM Model 9

10. 10 Overland Direction Channel Flow Characteristics Infiltration Excess Calculated at Each Cell  Rainfall Rate  Infiltration Rate  Runon From Upslope

11. Whooo!! 11

12.  Created storage- elevation relationships with GIS  Rating curves developed with spillway equation 12

13.  Ordered NEXRAD-Radar Rainfall data  April 2009 event and Hurricane Ike  Calibrated model at Sawdust Rd. (USGS gage 08068450)  Calibration adjustments:  channel cell and overland cell roughness ▪ Mostly effected timing and peak flows  Initial saturation  Hydraulic conductivity 13

14.  4% volume difference  3% peak flow difference  2.3 hr time to peak difference  8,000 cfs peak Avg. channel n = 0.026 Avg. land n = 0.038 Avg. In. Sat. = 9% Avg. K = 2.12 in/hr 14

15.  16% volume difference  37% peak flow difference  0 hr time to peak difference  3500 cfs peak Avg. channel n = 0.026 Avg. land n = 0.038 Avg. In. Sat = 54% Avg. K = 1.41 in/hr 15

16.  Even with no losses the peak flow is under-predicted  Conclude that the Radar Rainfall does not accurately represent entire event Avg. channel n = 0.026 Avg. land n = 0.038 Avg. In. Sat = 100% Avg. K = 1.41 in/hr 16

17. Five historical storm events 1979 USEPA study on The Woodlands 17

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19.  1983 USGS LandSat image to verify pre-development land use type  Manning’s roughness value for forest and woody wetland vegetation  Initially set n = 0.094 19

20.  Undeveloped model matches observed historical flows  Channel n = 0.032  Overland n = 0.066 20

21.  2006 development causes about 100-200 cfs increase in peak flow  Some shift in timing  Design of The Woodlands effectively mitigates the impact of development on hydrology 21

22.  Existing Cypress Creek Vflo TM model used to average roughness and impervious values for Houston highly urbanized areas  n = 0.024Imperviousness = 27%  Added roughness of 0.015 for all channel cells to represent a hypothetical concrete channel network 22 Replace with this…

23.  Channel n = 0.015  Overland n = 0.024  Drastic change in timing and peak flow 23

24. Peak Flow Comparisons (cfs) Undeveloped 2006 Development (% diff.) Intense Development (% diff.) 10/28/1974375573 (53%)1543 (312%) 11/10/1974825952 (15%)3301 (300%) 11/24/1974755807 (7%)2102 (178%) 12/10/1974500491 (2%) - Hurricane Ike61128119 (33%)17017 (178%) Avg. Diff. -22%242% Time to Peak Comparisons (hrs) Undeveloped 2006 Development (∆ hrs) Intense Development (∆ hrs) 10/28/19742014.67 (5)7.5 (12.5) 11/10/1974155.0 (10)2.8 (12) 11/24/19742613.3 (13)5.5 (21) 12/10/197427.35.33 (22) - Hurricane Ike16.85.66 (11)1.5 (15) Avg. Diff. -12.5 hrs15.1 hrs 24

25.  Can Vflo TM accurately predict stormwater runoff from small sub-areas within the watershed?  Select small sub-areas within the calibrated model of The Woodlands ▪ 10 – 200 acres in size  Compare to peak flows calculated from the Rational Method 25

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