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Greater Houston Area Elevation Analysis
by Davis Tolman([email protected])
Exploring the data for subtle insights...
I started with high-resolution elevation data obtained from ArcGIS Online Data Source *
Greater Houston Area – Elevation
Data Type: ArcGIS Image ServiceService Name: WorldElevation/TerrainConnection: InternetServer: https://elevation.arcgis.com/arcgis/services
*
... changed to a yellow to blue color bar to show detail
Greater Houston Area – Elevation
…. made the layer transparent to show Houston and the surrounding area
Greater Houston Area – Elevation
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)
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)
Terrain layer made partially transparent to show road system.
Greater Houston Area – 10th Order Residual
Color bar rescaled to highlight some of the growth fault trends that exist NW of Houston
Greater Houston Area – 10th Order Residual
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.
Buffalo Bayou
Greens BayouCypress Creek
White Oak Bayou
Brazos River
Brays Bayou
Sims Bayou
Oyster Creek
Addicks Reservoir
Barker Reservoir
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.
Houston Area Detail – 10th Order Residual
Transparent to show location
Buffalo Bayou
Greens BayouCypress Creek
White Oak Bayou
Brazos River
Brays Bayou
Sims Bayou
Oyster Creek
Addicks Reservoir
Barker Reservoir
West Houston Area Detail – 10th Order Residual
Colorbar selected to enhance subtle faults in the Buffalo Bayou / Memorial area.
Buffalo Bayou
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
N Houston Area Detail – 10th Order Residual
Note that one fault trends towards the NW corner of Bush Airport
Greens Bayou
N Houston Area Detail – 10th Order Residual
Transparent to show location
Can residual elevation maps provide insight into areas of
potential flooding?
Brays Bayou Example:
SW Houston Area FEMA Flood Designation
Note large 100 year floodplain area along Brays Bayou
500 yr floodplai
n
100 yr floodplain
Minimal Flood Risk
Brays Bayou
SW Houston Area - Elevation
Raw Elevation for SW Houston
SW Houston Area – Regional Residual Surface
10th Order surface from raw elevation
SW Houston Area – Residual Elevation
Residual Elevation = (Raw Elevation – Residual) … box shows zoom to Brays Bayou
500 yr
100 yr
Minimal
Brays Bayou – FEMA Floodplain Designation
FEMA Floodplain Designation along Brays Bayou
Brays Bayou Area – Raw Elevation Data
Raw elevation map does little to predict FEMA floodplains along Brays Bayou
Brays Bayou – Residual Map shows Subtle Relative Elevation Detail
Residual Map – Reds relatively high; Blues relatively low
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
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 ([email protected])
