Morphodynamic regime change in a reconstructed lowland stream

摘要

With the aim to establish and understand morphological changes in response tochannel reconstruction, a detailed monitoring plan was implemented in alowland stream called Lunterse Beek, located in the Netherlands. Over aperiod of almost 2 years, the monitoring programme included serialmorphological surveys, continuous discharge and water level measurements, andriparian vegetation mapping, from photographs and field surveys.Morphological processes occurred mainly in the initial period, beforeriparian vegetation developed. The initial period was largely dominated byupstream sediment supply, which was associated with channel incision upstreamfrom the study area. Herbaceous vegetation started to develop approximately 7months after channel reconstruction. The monitoring period included twogrowing seasons. A clear increase of riparian vegetation cover from first tothe second year was observed. Detailed morphological and hydrological datashow a marked difference in morphological behaviour between thepre-vegetation and post-vegetation stage. A linear regression procedure wasapplied to relate morphological activity to time-averaged Shields stress. Inthe initial stage after channel reconstruction, with negligible riparianvegetation, channel morphology adjusted, showing only a weak response to thedischarge hydrograph. In the subsequent period, morphological activity in thechannel showed a clear relation with discharge variation. The two stages ofmorphological response to the restoration measures may be largely associatedwith the upstream sediment supply in the initial period. Riparian vegetationmay have played a substantial role in stabilizing the channel banks andfloodplain area, gradually restricting the morphological adjustments to thechannel bed.