Alluvial floodplains contain four types of abandoned channels: old river courses, oxbow lakes, oxtail lakes and riparian wetlands. These result from avulsions, meander cutoffs, ice-jam floods and stem-channel shifts, respectively. With the exception of old river courses, which belong to terrestrial ecosystems, abandoned-channel types are important components of freshwater ecosystems. During 2006-2009, we conducted systematic investigations of macroinvertebrates in three types of freshwater abandoned channels and identified 93 taxa of macroinvertebrates belonging to 51 families and 88 genera. In the assemblage composition, most taxa were similar to those found in riverisolated lakes and river mainstreams. Moreover, abandoned channels supported many unique benthic taxa, which are important complementary resources for the entire river system. In the abandoned channels that were covered with a layer of silt, standing crops were higher than that found in the river mainstream where the bed sediment consisted mainly of sand. Conversely, in abandoned channels that were covered with fine sand, standing crops were lower than in the gravel streambed. Some abandoned channels, such as the riparian wetlands of the East River that are freely connected with the mainstream, were characterized by the highest biodiversity and the greatest biomass. In regions less affected by human activities, abandoned channels need to be connected with mainstreams by flooding at least once every 3 years to maintain at least half of the maximum amount of macroinvertebrate resources. In regions more affected by human activities, abandoned channels need to be connected with mainstreams at least once every year.

In 1996 and 1998 several devastating floods occurred on the Yangtze, Yellow, Haihe and Songhua Rivers in China. Flood disasters are now happening more frequently than in the past, due to the fact that economic development is changing the river discharge and the flood control system has not matched the change. In recent years it has been found that small floods cause high stage and extreme damage on the Yellow and Yangtze Rivers, which is due to the non-integrated water and sediment management. On the Yellow River a flood in 1996 with a return period of two years caused the highest recorded stage in history and resulted in huge economic losses because the high rate of siltation and the increasing water diversion from the river had greatly reduced the flood discharge capacity of the river channel. In the Haihe River basin a 1-in-50-year flood in 1996 claimed fewer lives and less damage than in earlier times thanks to artificial drainage canals built in the 1960s and 1970s, which increased the capacity of the drainage system tenfold. New problems arise, however, because due to sediment carried by the tidal current from the sea, the channel outlets are congesting. On the Yangtze River an extreme flood occurred in 1998 which resulted in serious flood damage and affected 8 million people. It was primarily a result of abnormal heavy rainfall, but the flood stage was extremely high due to a reduced flood diversion, reduced regulation capacity of riparian lakes, and channel sedimentation. This paper describes recent flood events and discusses new strategies for flood control.

Benthic macroinvertebrates are organisms primarily living in the streambed. The stability of the streambed is of vital importance to macroinvertebrate assemblages. Measurement of the streambed stability and sampling of macroinvertebrates were performed from 2005 to 2011 in four mountain streams: the Shengou, Diaoga, Jiangjia and Dabaini Rivers, which have different stability and are all located in the Yunnan plateau in southwestern China. The Shengou, Diaoga and Jiangjia Rivers are composed of gravels and cobbles, and the Dabaini River is mainly composed of gravels. The streambed stability was determined by the ratio of time over the sum of erosion and deposition areas of sediment per unit streambed width at each measured cross‐section. The Shengou River had the highest stability, followed by the Diaoga and Jiangjia Rivers. The Dabaini River had the lowest stability. A total of 70 taxa of macroinvertebrates belonging to 45 families and 68 genera were identified in these streams. Arthropods were the dominant taxonomic group. Collector gatherers had the highest density. Taxa richness, Shannon–Weaver index and K‐dominance curve were used to assess the biodiversity of macroinvertebrates. Results showed that the Shengou River had the highest biodiversity, followed by the Diaoga and Jiangjia Rivers. The Dabaini River had the lowest biodiversity. The detrended correspondence analysis ordination indicated that the streambed stability was the main factor that influenced macroinvertebrate assemblages, counting for 22.7% of the variance. The biodiversity and wet weight of the macroinvertebrates were highly dependent on the streambed stability. The biodiversity increased with the streambed stability and reached equilibrium when the stability was over 20 year m−1. The wet weight of macroinvertebrates showed an increasing trend with the streambed stability. However, no clear relation was identified between the density of macroinvertebrates and the streambed stability. It was concluded from this study that, in order to improve the ecological condition within the mountain streams, erosion and sedimentation must be controlled to enhance the streambed stability. Copyright © 2014 John Wiley & Sons, Ltd.

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