Preventing Water Erosion: A Site Assessment Checklist for Spotting At-Risk Ground Early

Structural failure in critical infrastructure and coastal assets is frequently traced back to water erosion, and routine site inspection is what catches the problem while it’s still manageable. But knowing erosion is a risk isn’t the same as knowing how to identify erosion risk on a given site. 

A site assessment checklist for preventing water erosion bridges that gap. It converts broad awareness into a specific, repeatable procedure that can be run on any walkover, whether the asset is a bridge, a riverbank, a weir or a port structure.

This guide sets out that checklist: the signs of scour, undercutting, sediment loss and ground movement to check for, how often a site should be inspected, and the point at which a finding should go to an engineer rather than stay on a monitoring list. It also looks at why the right countermeasure depends on the site itself, and where Bluemont Rock Bags™ fit into reducing that risk.

What Drives Erosion Risk on Australian Sites

Australian erosion risk is shaped by extremes rather than steady conditions. The intensity of short-duration, hourly-scale extreme rainfall events has increased by around 10% or more in some regions over recent decades, with the largest increases typically in the north of the country, according to the Bureau of Meteorology and CSIRO’s State of the Climate 2024 report.  It’s the velocity of water hitting a bank, weir toe or bridge pile that contributes to much of the damage, not the total rainfall over a season.

Catchment scale adds to this. A weir on a major river system can be managing runoff from a catchment the size of a small country during one flood event, so the hydraulic load at a single point can be far higher than a calm day suggests.

Site type varies the risk further. Queensland and northern NSW catchments see high-sediment wet season flows. The Pilbara sits dry for long stretches then converts to high-velocity flow within hours. Remote outback infrastructure faces both extremes, plus infrequent inspection access. Coastal sites are another slower driver: sea level around Australia has risen roughly 3.3mm a year since 1993, reaching up to 5mm in the north.

Why Early Assessment Is Important

Austroads’ national guidance on bridge flood resilience, released in October 2025, recommends regular scour risk assessments, structured condition inspections, and prioritisation of high-risk assets, on the basis that a structure judged adequate at one inspection can be exposed differently by the next flood event. The same logic applies to any structure facing concentrated flow, a weir toe or a wharf as much as a bridge pier.

Early assessment is as much practical as financial. A site treated while erosion is still localised needs less material, less plant and a shorter window on site than one where a footing has already failed. Once failure occurs, the job usually becomes a full rebuild. This includes new footings, engineering sign-off, and often a longer closure while work is carried out. 

The Insurance Council of Australia puts average annual insured losses from extreme weather at $4.5 billion between 2019 and 2024. It’s a 67% increase on the previous five years, prompting industry calls for a $30.15 billion, ten-year Flood Defence Fund. Intervening before failure is consistently cheaper than intervening after it.

The Site Assessment Checklist: What to Look For

The erosion control checklist below covers four categories of warning signs: scour, undercutting, sediment loss, and vegetation or ground movement, along with how often to check and when a walkover on its own isn’t enough.

Assessments don’t have to require specialist equipment or training. What’s more important is knowing what to look for, and walking the site at the right time to see it.

When and how often to check

A single inspection only tells you the state of a site on one day. Erosion risk moves with the seasons and with individual storm events, so timing matters as much as knowing what to look for when it comes to preventing water erosion.

Routine walkover

Check most sites twice a year, heading into the wet or storm season for your region and again coming out of it. This picks up gradual change before the next event puts it under pressure.

After significant rain or high flow

Inspect within a few days. Evidence of scour or bank loss fades quickly once the next rain event moves through.

Ahead of a development approval or capital works decision

Carry out a fresh assessment as standard practice before lodging a development application or setting a capital works budget, since decisions need to reflect current site conditions rather than an outdated inspection.

After anything changes upstream

New development, a realigned channel, or a structure built nearby can redirect flow onto ground that was previously stable. That’s worth checking outside the normal schedule.

There’s no single cadence that suits every site. A port facing regular vessel traffic and a grazing property in the outback don’t erode on the same clock, so treat the above as a starting point rather than a replacement for judgement on the specific asset.

Signs of Scour

Scour is localised removal of bed or bank material by concentrated flow, most common at structures that disrupt flow: bridge piers, weir toes, culvert outlets, port and wharf faces.

• Exposed footings, piles or foundations that were previously covered by bed material
• Depressions or holes in the streambed or seabed immediately downstream of a structure
• Undermined riprap or rock armour, where individual rocks have shifted or rolled away from their original position
• A visible drop in bed level at pinch points, culvert mouths and weir aprons

Signs of undercutting

Undercutting happens below the waterline or below the visible bank face, so it’s often missed until the bank above it collapses.

• An overhanging bank edge, sometimes with vegetation still rooted in soil that has lost its underlying support
• Slumping or a stepped bank profile, where a section has dropped relative to the ground above and below it
• Cracks running parallel to the bank line, a few hundred millimetres to a few metres back from the edge
• Recently exposed tree roots along a bank that previously showed none

Signs of sediment loss

Sediment on the move is erosion in progress somewhere upstream, even if the site in front of you looks stable.

• Persistent turbidity in a waterway after flow has otherwise settled following rain
• Sediment fans or deposits at the base of slopes, culvert outlets or drain junctions
• Bare, compacted or rilled ground where topsoil has visibly thinned
• A channel that has visibly widened, straightened or shifted position compared to earlier site records or aerial imagery

Vegetation and ground movement

Vegetation is a slow-moving indicator, which makes it useful for picking up erosion that hasn’t yet produced a dramatic failure.

• Tilting or leaning fence posts, power poles or trees along a bank or slope, all leaning the same direction
• Bare, scalped patches on sloped grazing land, particularly after heavy rain
• New rill or gully channels forming across paddocks or embankments, even shallow ones
• A track, access road or driveway edge that has narrowed or lost material along one side

When to Escalate to a Formal Assessment

A checklist tells you where to look closer, not whether to act.

Bring in a geotechnical or coastal engineer, or your state or local council’s natural hazards team, when you see active undercutting near a structure carrying load, such as a bridge, weir or building, when a bank or slope has moved measurably since the last inspection, or when a site sits inside a mapped hazard zone under your state or council planning framework. At that point, a formal assessment is what determines whether the site needs monitoring, remedial work, or a change in use.

Quick Reference Checklist

Print or save this section for a site walkover.

• Exposed footings, piles or foundations previously covered by bed material
• Holes or depressions in the bed immediately downstream of a structure
• Rocks shifted or rolled out of an existing riprap or rock armour layer
• Overhanging or undercut bank edge
• Slumping, stepped bank profile, or cracks running parallel to the bank
• Recently exposed tree roots along a bank
• Persistent turbidity after flow has otherwise settled
• Sediment fans or deposits at slope bases, culvert outlets or drain junctions
• Leaning fence posts, poles or trees along a bank or slope, all in one direction
• Bare or scalped patches on sloped grazing land
• New rill or gully channels, even shallow ones
• Narrowed or lost material along a track, driveway or access road edge

Any single item on its own may be minor. Two or more on the same site, or one item worsening between visits, is the signal to escalate.

Preventing Water Erosion at an Early Stage: Where Bluemont Rock Bags™ Fit