greater houston area elevation analysis

Greater Houston Area Elevation Analysis

by Davis Tolman(dntolman@gmail.com)

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 (dntolman@gmail.com)