Assessing river condition: A multiscale approach designed for operational application in the context of biodiversity net gain

Abstract

Assessments of river condition are needed to guide all aspects of river management. Such assessments have evolved over three decades from simply capturing the mosaic of river physical habitats to recognizing that habitat mosaics are dynamic, driven mainly by physical processes and modified by human (indirect) pressures and (direct) interventions. To embrace these broader aspects, riparian as well as in-stream environments need to be evaluated, going beyond subjective assessments to incorporate observations that support understanding of both physical habitat structure and cause-effect relationships. This paper reports on an operational approach to assessing the physical condition of rivers, which attempts to bridge the gap between a physical habitat and a geomorphic condition assessment. The approach forms part of Biodiversity Metric 2.0, a habitat-based methodology for measuring and accounting for biodiversity losses and gains resulting from development or land management change at individual project sites across England. The river condition assessment component adopts a bottom-up multi-scale approach that integrates field observations of physical habitats and of features indicative of geomorphic processes to deliver assessments of longer subreaches, whose condition is then evaluated within the context of the reach-scale geomorphological type of river. By applying the assessment before, immediately after, and following recovery from project implementation, changes in condition and their causes can be evaluated. The assessment method is presented to an international audience, outlining its structure, application and testing, and critically discussing its strengths and weaknesses, because the methodological approach could be helpful for devising methods for application in other environmental contexts.

Assessment of the geo‐eco‐hydrological condition of anabranching reaches in the Source Zone of the Yellow River, western China

“…Rather than consider attributes of condition/health as separate layers, a coherent approach appraises process-based measures to assess the integrity and function of the system as a whole (Brierley, Reid, Fryirs, & Trahan, 2010;Gurnell et al, 2020). This incorporates appropriate measures of geophysical integrity and connectivity that sustain the functional (material and energy flux) integrity of the river system under investigation.…”

Things we can do now that we could not do before: Developing and using a cross-scalar, state-wide database to support geomorphologically-informed river management

“…Similar approaches to analysis in other parts of the world have built upon these principles (e.g. European MQI [ 74 , 75 ]; UK MoRPh [ 76 , 77 ]).…”

The legacy of river channel modification in wadeable, lowland rivers: Exploring overdeep rivers in England

“…Robustly estimating the morphological legacy of human actions in the lowlands thus requires large data sets that can override the 'noise' inherent in analysis of individual channels, but regionallyextensive river geomorphological databases are rare. However, some geomorphological information can be extracted from river habitat surveys which are widely collected to support river assessment and management (Belletti et al, 2015;Gurnell et al, 2020) and often include records of channel dimensions and bed materials. Furthermore, such data are being increasingly collected by volunteers as well as river professionals.…”

“…Furthermore, such data are being increasingly collected by volunteers as well as river professionals. Here, we reveal potentially significant research results from an initial analysis of such a data set collected using the Modular River Physical (MoRPh) survey, a geomorphologicallyinformed habitat survey designed for use by volunteers (Shuker et al, 2017;Gurnell et al, 2019) and recently by river professionals in determining river condition (Gurnell et al, 2020). The MoRPh survey has been applied extensively in small rivers and streams.…”