CONFINED-WATER HYDROGRAPHY · QUEENSLAND

Crystal Cascades MBES Survey

High-resolution bathymetric mapping in a confined plunge pool

Client

Tailored Spatial Solutions

Region

Crystal Cascades, Cairns, QLD

Fieldwork

15–17 January 2026

QOffshore role

Hydrographic survey support & reporting

Platform

Uni-Mini ASV + NORBIT iWBMS

Processing

Qinsy acquisition + Qimera QC

The client issue

Tailored Spatial Solutions required a reliable bathymetric model of the Crystal Cascades plunge pool immediately upstream of a concrete dam/weir. The survey needed to define underwater topography and depth, identify significant submerged features and potential sediment accumulation or erosion, and provide high-resolution data suitable for hydraulic modelling and engineering design.

883.4 m²

Survey area

2,505.2 m³

Estimated volume

0.25 m

Grid resolution

±0.15 m

Vertical uncertainty (95%)

The survey challenge

High-energy confined geometry

Strong turbulence near the waterfall and steep rock-bounded margins limited safe vessel proximity and conventional access.

Shallow, irregular margins

Shallow water near the dam/weir and inflow sector reduced swath coverage and required careful, adaptive manoeuvring.

GNSS beneath dense canopy

Vegetation intermittently degraded PPP corrections. INS bridging maintained continuity while the controlled waterline strengthened vertical consistency.

Survey delivery

The workflow used a Unique Group Uni-Mini autonomous surface vessel carrying a NORBIT iWBMS multibeam system with integrated INS/GNSS. Qinsy supported acquisition, navigation monitoring and real-time DTM coverage; Qimera supported navigation review, sounding cleaning and final surface generation. Sensor offsets were measured during mobilisation, an in-situ patch test verified alignment, and Fugro Marinestar G4+ PPP corrections supported positioning. With the dam/weir holding the water surface effectively constant, final bathymetry was referenced to a controlled waterline elevation of 182.4 m AHD.

Outcome and client value

The survey defined a basin approximately 70 m long, with observed depths reaching about 5.8 m below the controlled waterline. The deepest zone occurs in the southwest near the waterfall inflow, with progressive shoaling toward the northeast dam/weir. No significant artificial obstructions or debris were identified, and no pronounced scour hole was observed immediately upstream of the dam. The dataset provides a coherent single-epoch baseline for engineering interpretation, hydraulic modelling, volume estimation and future comparative assessment.

Survey deliverables

0.25 m bathymetric DTM and cleaned soundings
Contours, spot depths and longitudinal profiles
Bathymetric contour, shaded-relief and spot-depth charts
Depths referenced to the 182.4 m AHD controlled waterline
Baseline dataset for hydraulic, volume and morphology assessment

Why it mattered

A compact ASV, adaptive acquisition and a stable waterline datum converted a narrow, turbulent and canopy-obstructed plunge pool into a high-resolution bathymetric model. The approach prioritised safe access near the waterfall, preserved vertical consistency despite intermittent GNSS corrections, and delivered a traceable baseline for engineering use.

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