Abstract
Mapping fluvial hydromorphology is an important part of defining river
habitat. Mapping via field sampling or hydraulic modelling is however
time consuming, and mapping hydromorphology directly from remote sensing
data may offer an efficient solution. Here we present a system for
automated classification of fluvial hydromorphology based on a deep
learning classification scheme applied to aerial orthophotos. Using
selected rivers in Norway, we show how surface flow patterns (smooth or
rippled surfaces versus standing waves) can be classified in imagery
using a trained convolutional neural network. We show how integration of
these classified surface flow patterns with information on channel
gradient, obtained from airborne topographic LiDAR data, can be used to
compartmentalize the rivers into hydromorphological units that represent
the dominant flow features. Automated classifications were consistent
with those produced manually. They were found to be discharge-dependent,
showing the temporally dynamic aspect of hydromorphology. The proposed
system is quick, flexible, generalizable, and free from
researcher-subjectivity. The deep learning approach used here can be
customized to provide more detailed information on flow features, such
as delineating between standing waves and advective diffusion of air
bubbles/foam, to provide a more refined classification of surface flow
patterns, and the classification approach can be further advanced by
inclusion of additional remote sensing methods that provide further
information on hydromorphological features.