Experiments on Channel Evolution due to Dam Removal in Taiwan

Due to safety concerns and habitat restoration for landlocked salmon,a 13-m high check dam on Chijiawan Creek was removed in late May 2011 in Taiwan.We conducted experiments to understand channel evolution of different scenarios.We further compared our experimental results of riverbed elevation changes with the analytical solutions derived from the diffusion equation and field dynamics as well after the creek experienced the first flood event.The results indicated that magnitude of discharges and notch size are dominant factors in resulting channel evolution.While the largest differences between grain size distribution are associated with discharge,the largest differences in net change in upstream volume are associated with notch size.While the theoretical equation could help understand the channel change after dam removal,it only explained the evolution closer to the dam.The physical experiments,on the other hand,provided insights especially with regard to comparing alternative proposed management actions.The discrepancies between predicted and actual outcome highlight more needed inputs for future dam-removal assessments.

Natural Processes for the Restoration of Dam Removal Disturbances

The Heber River Diversion Dam （Heber Dam） and 3.6 km penstock on Vancouver island, British Columbia, Canada was built in 1953 and by 2009, it had reached the end of its useful life due to the deteriorated wooden structures. A decision was taken to remove the dam, return the flows in the Heber River to pre-dam conditions and restore the footprint of the dam and penstock. Plans were developed for removal of the dam and contaminated materials including the creosote coated wooden penstock and other wooden structures associated with the dam and site restoration. Work on removal and restoration was undertaken over the summer and fall of 2012 and the spring of 2013. Restoration treatments were based on the use of natural processes as a model for recovery. The recovery of dam and penstock removal disturbances was initiated in the late summer and fall of 2012 with the fall dispersal of seeds from mature pioneering species that formed a significant part of the local undisturbed vegetation. This paper describes the treatments that were applied to enhance the natural recovery of the disturbed areas and the results of those treatments. The restoration treatments were designed to address the filters that were present in project areas. These were identified during an initial inspection in 2009 and were centred on compaction of substrates and a lack of micro-sites. In addition to the use of natural processes for the restoration of project disturbances, a local First Nations crew was hired to transplant sword ferns （Polystichum munitum （Kaulf.） C. Presl） from the adjacent forest areas onto project sites to provide a social benefit from the restoration work.

The Socio-Economic Impacts of Aged-Dam Removal: A Review

Water storage dams worldwide are ageing, and many will reach the end of their designed lifespan by the middle of the 21st century. Some of these dams will likely need to be removed. While dam construction impacts have been widely discussed, dam removal impacts on society and the economy need to be synthesized and considered in the ageing dams’ decision-making process. This paper summarizes dam removal impacts on the local economy and industry, culture, history and heritage, property value, recreation, aesthetics, and disaster avoidance from identified studies worldwide. It demonstrates that these impacts may vary depending on geography and between developed and developing countries. It concludes that dam removal should consider the cost, environmental, and the socio-economic impacts while including all stakeholders who could be positively and negatively impacted by dam removal.