River Sedimentation – Wieprecht et al. (Eds)© 2017 Taylor & Francis Group, London, ISBN 978-1-138-02945-3

Economic assessment of the effects of sediment replenishment to rivers andthe effectiveness of sediment management
K. Tomita & T. Homma
Civil Engineering And Eco-Technology Consultants Co., Ltd., Tokyo, JapanT. Sumi
Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Kyoto, JapanABSTRACT
Japan is characterized by steep mountain topography
and weak geology as well as high precipitation andseasonal drastically changing temperature. As a result,sediment produced in mountain areas is frequently
transported downstream and supplied to coastal areas
through the river mouth which has formed many alluvial fans. In these upstream mountain rivers, manystorage dams have been constructed for the purposeof flood control and water utilization. Nowadays, sediment accumulation in their active storage volume
is a crucial issue both for reservoir and river basinsustainability.
In Japan, several countermeasures such as excavation, dredging, draw down flushing and bypassing havebeen introduced to solve this issue. This paper studies
the effects of sediment replenishment with a sediment
bypass project which restores sediment movement to
the original condition and evaluates the project quantitatively by converting the effects to economic value tothe extent possible. Additionally, the paper examines
optimization of sediment replenishment by conducting sensitivity analysis to know how the effects change
through implementation of sediment management.
As a case study, we have selected the Yahagi River
where integrated sediment management in a river basinwith a proposed sediment bypass tunnel at the Yahagi
dam is undergoing. Based on several scenarios, wehave conducted economic analysis considering bothadvantage and disadvantage points of sediment replenishment. We have also studied the effects of sedimentmanagement to control shape of reservoir sedimentaccumulation in the reservoir regarding the quality
control in the reservoir. Additionally, based on theamount of necessary sediment excavation volume formaintenance the river channel and downstream reservoir areas after the operation of sediment flushingBP, we studied measures for effective use of sedimentresources by sediment nourishment for river-mouth,

estuary and coastal areas and recycling for construction materials. In the case, we considered possible
site of stockyard where receiving unstable volumesof excavated sediment and delivering these recyclingsites continuously.
In this study, historical study is done over dam
and rivers and added with cost-benefit analysis ofsediment BP over the estuary and coastal zone. Furthermore, in order to enhance the effectiveness andaccuracy, estimation of sediment volume inflow of thedam using rainfall data, landslide data, etc. is included
into analyzing process.
In the normal basin, sediment is produced in thebare land of landslide trace and supplied to the river
channel by the action of gravity, wind, surface flow, etc.
When sediment supply into river channel is abundant,talus is formed. Then, erosion of talus supplies sediment volume to the river channel. During heavy rain,
bare land gets wider, then, sediment production from a
new collapse area occurs rapidly which increases sediment production and supply system. These processes
are added into previous model, then, applied on rivercase study.
Model is calculated with assumption of 50 years
stabilized sediment inflow into the dam and sedimentsupply from eroded area along the way. Then, the result
is verified with the real sediment inflow state, whichshows good correlation. This includes sediment production results in the rivers, dams region, estuary to thecoastal area, and sediment influx from terrain, geology,
from rainfall conditions. Moreover, cost-effectivenesscalculation of sediment BP can be constructed. It
should be noted that aerial photographs, geological
data, hydrological data for other dam are also available,thus, study to deter- mine the operation of sediment BP
is possible.
From now on, the review and implementation propriety of sediment BP of dam both inside and outside
Japan and case study to determine economic effect,
etc. are increasing.

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