Ngaroto Lake Bathymetric & Side-Scan Survey

Overview

MĀKI conducted a comprehensive bathymetric and side-scan sonar survey of Lake Ngaroto — a 108-hectare Waipā peat lake — over three days on site. Using a custom autonomous inflatable e-kayak fitted with CHIRP MEGA SI sonar, the team produced a complete depth map, 3D bathymetric model and side-scan imagery of the lake floor, revealing unexpected underwater features including a structure of unknown origin.

The Challenge

Lake Ngaroto is a significant freshwater peat lake within the Waipā district, with motorboat restrictions in place to protect its sensitive ecology. These restrictions ruled out conventional survey vessels, making it one of many New Zealand lakes where traditional bathymetric methods are impractical.

The lake had not been comprehensively mapped, leaving managers without accurate data on its depth, volume, underwater topography or the condition of its bed — information essential for long-term ecological and hydrological management.

Our Approach

MĀKI deployed a compact autonomous inflatable e-kayak — quiet, low-impact, and well within the vessel restrictions applicable to the lake. The platform was fitted with a CHIRP MEGA SI sonar system capable of producing both precise depth readings and detailed side-scan imagery of the lake bed in a single pass.

Over three days, the vessel completed systematic survey transects across the full 108-hectare lake, collecting georeferenced depth and side-scan data at high resolution. The data was post-processed into a complete depth map, a 3D bathymetric model, and side-scan image mosaics that revealed the texture and features of the lake floor in detail not previously available.

Outcomes

The survey delivered a complete spatial picture of Lake Ngaroto's underwater environment for the first time — including the discovery of a 55-metre submerged structure of unknown origin revealed in the side-scan imagery. The depth model and volume calculations provide lake managers with a robust baseline for ongoing ecological monitoring and hydrological planning.