This paper assesses the feasibility of estimating water levels using
digital photogrammetry. A common problem during an extreme flood event
is that automated water level recorders do not record the highest water
levels, as a result of instrument malfunctioning. This paper explores
two possible solutions to this problem based upon data acquired using
synoptic remote sensing methods. The first method requires: (a)
high-resolution elevation data (for example, in the form of a digital
elevation model for the floodplain); and (b) information on the
planimetric position of the maximum flood extent, such as from debris
lines (known as wrack lines) visible on aerial imagery flown after the
event. The planimetric data can then be used to segment the topographic
data in order to identify water level elevations. The second method
uses a digitial photogrammetric approach and is suitable where no
topographic data are available, but aerial imagery is available, flown
after the event. Provided this imagery is of the right scale, digital
photogrammetric analysis may be used to identify the elevations of
wrack lines visible on the imagery. In this paper the second of these
options is compared with the first. The research shows that desktop
photogrammetric methods, using 1:4500 scale imagery, can yield water
level estimates that are precise to +/-0-147 m, on the basis of check
data obtained from lidar data. This is a worst possible estimate of the
acquired precision given uncertainties in the lidar data. When compared
with the first option, based upon segmenting lidar data using flood
outlines, the photogrammetric approach was found to be preferable given
both the quality of the lidar and uncertainties over how to segment it.