Research Trends and Results

Study on Maintenance Flow Rate Setting Procedure
for Rivers in Mountainous Area
KAWASAKI Masaki , Head; OTANI Amane , Researcher
Water Cycle Division, River Department
Keywords: renewable energy, small scale hydropower, rivers in mountainous area, river maintenance flow rate

2. Study method
This study is surveying, as model rivers, 4 rivers where
small scale hydropower systems have been introduced.
The study items have been limited to two considering thecharacteristics of rivers in mountainous area, i.e. impactof water intake on the habitats of living things and impacton landscape.
(1) Impact of water intake on habitats
By classifying the components of river channels inmountainous areas into step pool channels, cascadechannels, and riffle-pool channels, and defining each ofthem, the effect of flow rate decrease on habitats wasexamined for each component of the targeted river
channels. Considering that maintaining the habitats isimportant to reducing the impact of water intake on living
things and that no significant changes in physical quantity
including depth, velocity, water surface area, and watertemperature is important for maintenance, we did anhydrologic accounting by modeling each component of
the river channel and estimated what changes thedecrease in flow rate could cause to such physicalquantities (Figure).
Cross-section F (Step)
Cross-section E (Pool)
Cross-section D (Pool)

Water depth H (m)1. Background of study
The development of renewable energy is attracting
attention after the power supply shortage that followed
the Great East Japan Earthquake. Since a fixed pricepurchasing system for renewable energy started in 2012,
the purchase price of renewable energy has been rising.
For small scale hydropower, one of the renewableenergies, revisions to the River Law in 2013 allow
providers to register instead of requiring permission for
subordinate power generation using the existing water
utilization system since it is not expected to have new
impacts on river environments, etc. As a result,application documents and procedures were simplified
and the period required to obtain water rights was
significantly shortened.1)
In the case of new water intake, it is still required todetermine the river maintenance flow rate inconsideration of the impact on the river environment, etc.
However, for rivers in mountainous areas where small
scale hydropower is likely to be introduced, it would
require much time and effort to set the river maintenanceflow rate in the conventional manner since there is little
data or knowledge necessary for setting the rate.
Therefore, this study aims to facilitate water utilization
procedures for small scale hydropower by establishing asuitable and simple approach for setting river
maintenance flow rate for rives in mountainous areas.

Cross-section C (Pool)

Drought water discharge

Cross-section C (Pool)
Cross-section D (Pool)
Cross-section E (Pool)
Cross-section F (Step)

Flow rate Q (m3/s)

Figure: Example of Site and Hydrologic
Accounting(2) Changes in the landscape of rivers inmountainous area due to water intake
From past studies, it was found that people perceive agreater "amount of water" in areas whitened by ruffledwaves caused by a drop or otherwise in the stream.
Therefore, we conducted an experiment on landscapepreferences to study how people perceive the "amount ofwater" with photos taken of an actual river with the flowrate reduced in stages using a pump, and analyzed
correlations between the "perceived amount of water,"scale of ruffled waves, and various quantities of river.
3. Future plan
Based on the results of this study, we plan to propose areasonable method for setting flow rate for river
maintenance in mountainous area, and verify theapplicability thereof through case studies.
[Reference]
1) MLIT website
http://www.mlit.go.jp/river/riyou/syosuiryoku/index.html