Abstract
Recent legislative approaches to improve the quality of rivers have resulted in the design and implementation of extensive and intensive monitoring programmes that are costly and time consuming. An important component of assessing the ecological status of a water body as required by the Water Framework Directive is characterising the hydromorphology. Recent advances in autonomous operation and the spatial coverage of monitoring systems enables more rapid 3D models of the river environment to be produced. This study presents a Structure from Motion (SfM) semi-autonomous based framework for the estimation of key reach hydromorphological measures such as water surface area, wetted water width, bank height, bank slope and bank-full width, using in-channel stereo-imagery. The framework relies on a stereo-camera that could be positioned on an autonomous boat. The proposed approach is demonstrated along three 40 m long reaches with differing hydromorphological characteristics. Results indicated that optimal stereo-camera settings need to be selected based on the river appearance. Results also indicated that the characteristics of the reach have an impact on the estimation of the hydromorphological measures; densely vegetated banks, presence of debris and sinuosity along the reach increased the overall error in hydromorphological measure estimation. The results obtained highlight a potential way forward towards the autonomous monitoring of freshwater ecosystems.
Highlights
Legislative approaches have been introduced across the world with the intent of improving the quality of rivers since the second half of the 19th century [1]
Results for the Chicheley Brook showed that the number of points in the cloud gradually decreased as the stereo-camera height increased, with a difference of 5.3 million points between the cloud obtained at a height of 1.6 m and that obtained at 0.5 m
Extensive and intensive monitoring programmes for the characterisation of hydromorphology along rivers are required by multiple legislative approaches introduced with the intent of improving the quality of rivers
Summary
Legislative approaches have been introduced across the world with the intent of improving the quality of rivers since the second half of the 19th century [1]. An important component of WFD implementation is the development and implementation of monitoring programmes to characterise water bodies in terms of chemical, biological and morphological parameters This includes protocols such as the River Habitat Survey (RHS) [5] for the morphological assessment of reaches, the River Invertebrate Prediction and Classification System [6]. The increased need for monitoring has resulted in the rapid development of autonomous and wide-area monitoring techniques and technologies This is evident with hydromorphological characterisation where both hydrology (i.e., the quantity and dynamics of water flow and connection to groundwater bodies) and morphology (i.e., reach depth, structure and substrate of the river, structure of the riparian zone and river continuity) are measured [4]. Some of the approaches developed include, amongst others, the use of Unmanned Aerial Vehicles (UAVs) for continuous river habitat mapping [8,9], radio controlled boats with embedded sensors for hydromorphological characterisation [10,11,12,13] and the development of novel statistical methods for automated river environment data analysis [9,14]
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