Tracking Lateral Stream Instability with Geo-Referencing Tools

By Lana Potapova, E.I.T.

www.inftra.gov.ab.ca

What is lateral stream instability and why is it important to track it?

Why is tracking lateral stream instability important?

•River moved laterally and washed out 50m of fill

BF75904: HWY 33 over Island Creek

Why is tracking lateral stream instability important?

•Drift block at the bridge causes the water to take another path

Why is tracking lateral stream instability important?

•The river moved too close to the road as can be seen by the bank erosion

Why is tracking lateral stream instability important?

• This bridge is on poor alignment which causes many problems

BF78104: HWY 32 over McLeod River

Why is tracking lateral stream instability important?

•Poor alignment causes head-slope erosion

Local Road over Marten Creek

Why is tracking lateral stream instability important?

•Incorrect skew leads to drift accumulation at pier

Why is tracking lateral stream instability important?

•Incorrect skew leads to pier scour

BF 74710: HWY 40 over Berland River

How can lateral stream instability be tracked?

•Comparison of historic aerial photographs, satellite imagery, scour survey data, etc. •All these sets of data are to a different scale and comparing them side by side is hard

•Put some satelite pics here

What is Global Mapper Geo-Referencing?

•GIS software•Allows to compare digitized layers (aerial photos, surveyed data)

2006 Satellite Imageused as base layerbecause it is orthorectified(corrected for topography andangle of shooting)

• Insert a 2005 photo here

Why is tracking lateral stream instability important?

•Bridge failure due to pier scour

1980 photograph Geo-referenced

1980 zoomed in on the bridge

Now I would like to comparenot transparentlayersso I select one layer

Case Study: Little Red Deer River•Originally worried about a low spot in the road and the channel cutting off through the flood plain•No significant movement, so it’s low risk that the channel relocates but we’re still monitoring it•Discovered that the south bank upstream of the bridge is eroding•The bridge is new, so it matched the bank and right now it’s not at a risk – however, we are keeping an eye on it in the future•Currently it is monitored

Case Study: Freeman River•AIT was approached by Alberta Environment with concerns about bank erosion in the vicinity of the bridge

1951

1972

2002

2002Survey

D = 170m

•River used to be parallel to bank, now comes in at a sharp skew•Possibility of water outflanking our guidebank•Currently monitoring that region and we might need to extend the guidebank eventually

•The flow is deflecting off the bank•30 degree skewed flow at the bridge• Erosion of the bank•Eventually we mighthave look into extendingriver protection works there

Case Study: Drayton Valley•Used during bridge planning

Case Study: Drayton Valley•Geo-referencing allowed visualize flood extentsand flow profile

•Geo-referencingAlsoshowed that channel might be migrating and the spur can lose its function and that upstream alignment alternative are unfavorable from a river engineering perspective

Final Words on Geo-Referencing

• Not a substitute tool for any one feature; simply provides added value (i.e. we still use paper aerial photos with a stereopair to visualize things in 3-D)

• Final images provide documented evidence as a justification for spending money or choosing a certain design alternative

• This tool can be used for maintenance recommendations or as documentation during Level II BIM inspections of the channel

• Also useful during planning phase (Drayton Valley)• If we’re providing input into functional planning,

we’re hoping to use this tool to identify the least volatile region of the river for a potential crossing.

Any Questions?

www.inftra.gov.ab.ca