A geomorphic monitoring and adaptive assessment framework to assess the effect of lowland floodplain river restoration on channel–floodplain sediment continuity

Abstract

The state of the science of lowland river floodplain restoration reflects the relatively new and experimental nature of large river floodplain rehabilitation efforts. Based on results of a case study of floodplain restoration at the lowland Cosumnes River, California, we present a geomorphic monitoring and adaptive assessment framework that addresses the need to inform and utilize scientific knowledge in lowland floodplain river restoration activities. Highlighting hydrogeomorphic processes that lead to habitat creation, we identify a discharge threshold for connectivity and sediment transfer from the channel to the floodplain and integrate discharge magnitude and duration to quantify a threshold to aid determination of when geomorphic monitoring is warranted. Using floodplain sand deposition volume in splay complexes as one indicator of dynamic floodplain habitat, we develop a model to aid prediction of the sand deposition volume as an assessment tool to use to analyze future monitoring data. Because geomorphic processes that form the physical structure of a habitat are dynamic, and because the most successful restoration projects accommodate this fundamental characteristic of ecosystems, monitoring designs must both identify trends and be adapted iteratively so that relevant features continue to be measured. Thus, in this paper, adaptive assessment is defined as the modification of monitoring and analysis methods as a dynamic system evolves following restoration activities. The adaptive monitoring and assessment methods proposed facilitate long-term measurements of channel-floodplain sediment transfer, and changes in sediment storage and morphology unique to lowland river-floodplain interactions and the habitat that these physical processes support. The adaptive assessment framework should be integrated with biological and chemical elements of an interdisciplinary ecosystem monitoring program to answer research hypotheses and to advance restoration science in lowland floodplain river systems.

Evaluating stream restoration: A case study from two partially developed 4th order Connecticut, U.S.A. streams and evaluation monitoring strategies

“…Project evaluation is also needed to drive adaptive management and reduce the number of repeat failures (Johnson et al ., 2002). A tiered monitoring approach is adaptable to allow for tracking different system trends following stream restoration (Florsheim et al ., 2006). Furthermore, monitoring is needed so that the ranges of variability (Wohl et al ., 2005) and potential for recovery of a project can be better understood.…”

Nature rehabilitation by floodplain excavation: The hydraulic effect of 16 years of sedimentation and vegetation succession along the Waal River, NL

“…Reference lines are given for the 1982 sediment level, the discharge at which first inundation occurs and the discharge of first overbank flow (3435 m 3 s − 1 ). flow (m 3 ) across the floodplain (Middelkoop, 1997;Florsheim et al, 2006). Across-floodplain flow starts at flood levels of about 9.9 m, i.e., above a discharge of 3435 m 3 s − 1 .…”

Ecologically Functional Floodplains: Connectivity, Flow Regime, and Scale1

“…At the Cosumnes River floodplain (California), flows capable of depositing sand on the floodplain corresponded to a 1.5‐year recurrence interval (Booth et al. , 2006; Florsheim et al. , 2006).…”