Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics

Abstract

Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long-term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre-restoration and post-restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre-embankment and post-embankment conditions using the MIKE-SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m 3 s À1) and frequent localized flooding at the river edge during smaller events (>0.6 m 3 s À1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river-floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients.

Responses of fishes and lampreys to the re‐creation of meanders in a small English chalk stream

“…In the control reach, substratum composition did not change before and after the downstream rehabilitation work (analyses of variance, all p values >0.05; Figure b), but mean water depth declined by ≈23% in the control reach, from 24.1 ± 2.2 cm in 2009 ( n = 22) to 18.4 ± 1.5 cm in 2012 ( n = 27; F 1,21 = 5.78, p < 0.05) — this was due to seasonal differences in stream discharge (Clilverd et al, ) as well as reduced discharge in those years rather than to the downstream re‐meandering work (EA, unpublished data). Biotope proportions also varied with the incidence of riffle mesohabitats declining and the frequency of runs increasing after the downstream rehabilitation work (Figure ; one‐sample χ 2 test, p < 0.05).…”

“…The Glaven is alkaline (pH 7.7–8.0) and moderately mesotrophic, with mean nitrate and phosphate concentrations of 6.2 mg NO 3 − L −1 and 0.1 mg P L −1 mg L −1 , respectively (Clilverd , Thompson, Heppell, Sayer, & Axmacher, ). At Hunworth, mean annual river discharge from 2001 to 2010, measured at Environment Agency (EA) gauging station 034052, was 0.26 m 3 s −1 (min–max = 0.10–3.23 m 3 s −1 ), with lower discharge evident in summer compared to winter (Clilverd, Thompson, Heppell, Sayer, & Axmacher, ).…”

“…Rehabilitation works in the “treatment” study reach (≈370 m length) at Hunworth (52.882152°N, 1.0658938°E; elevation ≈20 m; Figure ) included embankment removal in March 2009 to re‐connect the river with its flood plain (Clilverd et al, , ; Figure b), followed in August 2010 by the re‐creation of meanders to increase channel sinuosity and instream habitat heterogeneity (Figures and c). Additionally, six parapotamon ‐type backwaters (sensu Amoros, Roux, Reygrobellet, Bravard, & Pautou, ) of 3–18 m length were created from the remnants of the former river channel (Sayer, ; Figure ).…”

Riparian research and legislation, are they working towards the same common goals? A UK case study

“…Nineteen percent of the publications found focused on the future outlook, current ecological status and impacts of riparian zones (Table S76) with land use change and restoration contributing the largest number of papers, representing 9% of the total. Studies within this category explored the effect of restoration and land use change on invertebrates (Harrison et al, 2004;Petersen et al, 2004), vegetation and floodplain dynamics (Clarke and Wharton, 2000;Clilverd et al, 2016), amongst others. There is evidence throughout history that riparian areas have been heavily affected by land use changes in order to increase agricultural productivity (Seavy et al, 2009;Poff et al, 2011).…”

Characterization of hydrology and water quality at a restored oxbow

“…The success of wetland projects depends on how these restored systems are connected to their floodplains. Understanding the effects of restoration on floodplain connection and river flow is essential to evaluate the success of the project (Clilverd et. al., 2016).…”