Narellan Creek Overland Flood Study (Vol 1) - Flipbook - Page 23
Narellan Creek Catchment
Flood Study
LiDAR provides a good description of ground elevations in areas of open space and lightly
vegetated areas.
However, LiDAR datasets can provide a less reliable representation of the terrain in areas of
high vegetation density. This is associated with the laser ground strikes often being
restricted by the vegetation canopy. Errors can also arise if non-ground elevation points
(e.g., vegetation canopy, buildings) are not correctly removed from the raw dataset.
Therefore, further interrogation of the LiDAR data was completed in areas of high
vegetation density.
Plate 1 provides an example of the LiDAR ground points in the vicinity of Fairwater Drive at
Harrington Park. Plate 1 confirms a high LiDAR point density across grassed and roadway
areas. Plate 1 also shows no ground points across buildings. Therefore, it appears that nonground points have correctly been removed from the LiDAR dataset and the LiDAR provides
a detailed description of the terrain in areas of open space.
Plate 1 shows that the point density significantly reduces in the vicinity of dense vegetation.
Therefore, there will be a less detailed representation of the variation in terrain in areas of
dense vegetation, including near creeks/watercourses. To better understand the ground
point density in areas of high vegetation coverage, the LiDAR ground point densities were
extracted from the raw LiDAR information and this information is included on Plate 2. A
detailed view of the ground point densities near Fairwater Drive is also provided in Plate 3.
Plate 2 shows that the point density across the catchment is most commonly above 20
ground points per square metre (in areas of flight line overlaps, the point density can exceed
40 points per square metre). However, Plate 3 shows that in areas of dense vegetation
coverage, the point density is generally no greater than 1 ground point per square metre.
Therefore, although a sub-1 metre DEM could be supported across most of the catchment, a
1 metre grid size is considered to be the smallest practical DEM grid size considering the
point density limitations across vegetated areas.
Furthermore, some creek lines comprise less than 1 point per square metre. Therefore, the
LiDAR DEM is unlikely to provide a reliable description of the conveyance capacity of these
waterways and will need to be supplemented with additional survey/data. Fortunately, the
available TUFLOW model includes additional terrain information along formal watercourses
to assist in overcoming the limited ground point information.
2.5
Geographic Information System (GIS) Data
A number of Geographic Information System (GIS) layers were also provided by Camden
Council to assist with the study. This included:
Aerial photography
Cadastre
Roads
LEP zones
Stormwater pits & pipes
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