Time and Intensity Weighted Indices of Fluvial Processes: a Case Study from the Kootenai River, USA

Abstract

Within riparian landscapes, river flows and stages determine habitat gradients from less to more dynamic, and these support different plant species and their life history stages that are adapted to specific positions along these gradients. The gradients are characterized by physical processes that vary in magnitude and duration, and these shape the riparian vegetation communities. Consequently, natural riparian ecosystems are very dynamic, and the river disturbance regime is essential for sustaining ecosystem health. However, although the importance of disturbance is well accepted, disturbance regimes are poorly understood. This study was undertaken to develop indices capable of characterizing riparian habitats by considering flood magnitude and the elapsed time after flood disturbance, that is, the history that influenced the present vegetation composition. The indices were tested along two reaches of the Kootenai River in Idaho, USA, with braided versus meandering channel forms. The case study spanned a 31‐year period and emphasized two major disturbance components, the morphodynamic influence of velocity and shear stress and the flood or inundation duration. Computed indices were tested for consistency and then used to characterize different riparian vegetation development and succession phases. The statistical analysis revealed high correspondence among the calculated indices and differences across the different successional stages and between the two reaches. This demonstrated the utility of the time and intensity weighted indices to analyse the fluvial patterns that support different riparian vegetation communities, and this could be applicable for riparian management, mitigation, conservation and restoration. Copyright © 2016 John Wiley & Sons, Ltd.

Exploring the key drivers of riparian woodland successional pathways across three European river reaches

“…The most prominent disturbance factors are probably those deriving from the morphodynamic disturbance and the flood inundation stress (Egger et al, ). Therefore, two different TIWIs have been proposed (Egger et al, ), MDi (morphodynamic disturbance) and FDi (flood inundation duration), which are calculated after Equations and . …”

“…and where the numerator of the MDi is calculated by summing the ratio of the maximum year‐round shear stress τ t (N m −2 ) withstood at each pixel divided by the corresponding year ordinal number (1980–2009) and that of FDi by summing the number of days y t (days year −1 ) flooded between April and September, which is likewise divided by the corresponding year ordinal number (1980–2009). That period corresponds to the primary interval of physiological activity of vegetation for temperate ecoregions of the northern hemisphere (Egger et al, ). Then, both sums are divided by the T th partial sum of the harmonic series, which is depicted at the denominator of the equations (see the lower sequence of Figure for a complete depiction of the water yield during vegetative period and the maximum annual flow at the three study sites).…”

The Role of River Morphodynamic Disturbance and Groundwater Hydrology As Driving Factors of Riparian Landscape Patterns in Mediterranean Rivers

“…In natural channels, shear stress is considered to be balanced by three resistance components, namely, viscous drag on the ground surface on particles, pressure drag associated with large non-vegetal boundary roughness and drag on vegetal elements ( Temple et al, 1987 ). The maps produced by River2D had a precision of a quarter of a square meter and were used to compute the MDi and the GWDi developed by Egger et al (2014 , 2016 ). Both are time and intensity weighted indexes (TIWI) that characterize the processes of grndh and mrphd of the historical flow regime in the past decade at each study site.…”

From Microhabitat Ecohydraulics to an Improved Management of River Catchments: Bridging the gap Between Scales

“…Egger et al () proposed reach‐scale "time and intensity weighted" flow indices that can reflect the history of flood magnitudes (velocities and shear stresses) and durations. These indices are derived from dynamic combinations of one‐ and two‐dimensional hydraulic models.…”

“…A relevant lack of recruitment of Salicacea pioneer species were found in regulated rivers, in coherence with hydrological changes such as flood disturbance decrease and summer minimum flows increase. Egger et al (2017) proposed reach-scale "time and intensity weighted" flow indices that can reflect the history of flood magnitudes (velocities and shear stresses) and durations. These indices are derived from dynamic combinations of one-and two-dimensional hydraulic models.…”