Simulation of hydrologic and geomorphic changes affecting a shrinking mire

Abstract

AbstractThe Kushiro Mire in subarctic Japan has significantly reduced in size because of the complex interaction of many processes, including snowmelt runoff, sediment transport and vegetation dynamics. This study uses a coupled integrated catchment‐based eco‐hydrology model with a mass transport process (NICE‐MASS) to investigate the influence of hydrologic and geomorphic changes on the Kushiro Mire. Coefficients of the sediment‐rating curve in the snowmelt runoff are very different from those in the snow‐free period. This empirical relation shall underestimate the observed suspended sediment (SS) concentration in the snowmelt period, indicating a difference in runoff mechanisms between the two periods and the necessity of a process‐based model. The simulation model reproduced well the spatial distribution of elevation aggradations by sediment deposits from rivers flowing into the mire. NICE‐MASS clarified that river channelization works carried out in the past resulted in groundwater degradation and drying phenomenon in the downstream area because of increased sedimentation and a decrease of seepage infiltration from the river to the aquifer. It is assumed that these hydrologic and geomorphic changes are closely related to the invasion of alder (Alnus japonica) into the mire. The occupation rate of alder is positively correlated with groundwater degradation relative to the ground surface. The model simulation derived by addition of this limiting factors related to submerged depth is important for prediction of vegetation succession when devising future policies for restoration of meandering river channels. Copyright © 2009 John Wiley & Sons, Ltd.