I used residual mapping techniques on high-resolution public elevation data to identify areas of active faulting and to identify areas ore prone to flooding. The results match well to the FEMA designations. Note: Very High Resolution Color Images - Best Viewed on Large Screen.

1. Greater Houston Area
Elevation Analysis
by Davis Tolman
(dntolman@gmail.com)
Exploring the data for subtle insights...

2. I started with high-resolution elevation data obtained from ArcGIS Online Data Source *
Greater Houston Area – Elevation
Data Type: ArcGIS Image Service
Service Name: WorldElevation/Terrain
Connection: Internet
Server: https://elevation.arcgis.com/arcgis/services
*

3. ... changed to a yellow to blue color bar to show detail
Greater Houston Area – Elevation

4. …. made the layer transparent to show Houston and the surrounding area
Greater Houston Area – Elevation

5. I generated a 10th Order smoothed surface (regional) from the total detailed terrain (see inset). Then this
regional surface was subtracted from total elevation map to arrive at the Residual Elevation Map ….
Greater Houston Area – Regional Elevation (smoothed)
(10th Order Polynomial)

6. Residual maps allow for local detail to be captured with a single color bar: Red=higher than regional; Blue=lower than regional.
Color bar was stretched to highlight the subtle elevation changes in the coastal plain counties of Harris and Fort Bend.
Greater Houston Area – Drainage Detail
(10th Order Residual)

7. Terrain layer made partially transparent to show road system.
Greater Houston Area – 10th Order Residual

8. Color bar rescaled to highlight some of the growth fault trends that exist NW of Houston
Greater Houston Area – 10th Order Residual

9. Houston Area – Zoom to faulted area in NW Houston
Active faults display small elevations changes at the surface, which show up as abrupt, linear color changes.
Brazos River
Addicks Reservoir
Barker Reservoir

10. Houston Area Detail – 10th Order Residual
BEG (Bureau of Economic Geology) mapped faults in the Houston area and likely faults (dashed) from this
interpretation. Close inspection shows many more subtle, linear fault features.

11. Houston Area Detail – 10th Order Residual
Transparent to show location
Brazos River
Addicks Reservoir
Barker Reservoir

12. West Houston Area Detail – 10th Order Residual
Colorbar selected to enhance subtle faults in the Buffalo Bayou / Memorial area.

13. West Houston Area Detail – 10th Order Residual
Transparent to show location. Note fault crosses close to the I-10 – Beltway 8 overpass exchange.
I-10
8

14. N Houston Area Detail – 10th Order Residual
Note that one fault trends towards the NW corner of Bush Airport

15. N Houston Area Detail – 10th Order Residual
Transparent to show location

16. Can residual elevation maps
provide insight into areas of
potential flooding?
Brays Bayou Example:

17. SW Houston Area FEMA Flood Designation
Note large 100 year floodplain area along Brays Bayou
500 yr
floodplain
100 yr
floodplain
Minimal
Flood Risk
Brays
Bayou

18. SW Houston Area - Elevation
Raw Elevation for SW Houston

19. SW Houston Area – Regional Residual Surface
10th Order surface from raw elevation

20. SW Houston Area – Residual Elevation
Residual Elevation = (Raw Elevation – Residual)
… box shows zoom to Brays Bayou

21. 500 yr
100 yr
Minimal
Brays Bayou – FEMA Floodplain Designation
FEMA Floodplain Designation along Brays Bayou

22. Brays Bayou Area – Raw Elevation Data
Raw elevation map does little to predict FEMA floodplains along Brays Bayou

23. Brays Bayou – Residual Map shows Subtle Relative Elevation Detail
Residual Map – Reds relatively high; Blues relatively low

24. Brays Bayou Area – FEMA Floodplain to Residual Comparison
Residual Map with FEMA Floodplain Designation Overlay. Residual closely
approximates the FEMA floodplain designations.
500 yr
100 yr
Minimal

25. Summary
• This residual mapping technique highlights local elevation differences.
• The Residual Map enhances our ability to identify of active surface faults.
• The Residual map may also highlight areas prone to local flooding.
I make no claims with regards to the accuracy of this experimental
technique’s ability to predict flood events and identify areas of faulting.
- Davis Tolman (dntolman@gmail.com)