TOPICS

Examination on method of setting theminimum water level for smooth introductionof small hydro power generation in
mountainous rivers

KAWASAKI Masaki , HeadTOYODA Tadahiro, Researcher
Water Management and Dam Division, River Department(Keywords) renewable energy, small hydro power generation, mountainous rivers, water utilization investigation
1. Background of research
Even today, the electric power situation is still criticalfollowed by the suspension of nuclear power plants inJapan after The Great East Japan Earthquake that
occurred in March 2011. Also in a future energy policy,“renewable energy” is gaining attention as
development of electric power resources without using
nuclear power. In such a situation, small hydro power
generation is expected to increase in the future because apurchase price of renewable energy has become higher
than the past after feed-in tariffs (FIT) for renewableenergy started on July 1st, 2012.
Under these circumstances, the Ministry of Land,
Infrastructure and Transport is now considering tosimplify the water utilization procedures relating to smallhydro power generation and encourage its introduction.
Especially, a mountainous river is a favorable
environment for small hydro power generation to be
introduced since its water is not used at present. However,since the form of mountainous rivers is different fromthat of rivers on the plains, knowledge concerning theeffects of water utilization on the rivers has not beenacquired. Therefore, it is difficult to decide easily under
the present condition whether or not the water should beused. For that reason, we examined a method ofdetermining the minimum water level of mountainousrivers.

Photo 1. Rivers under study (Kaji-gawa River inTottori Pref.)2. Contents of research
Although the minimum water levels of rivers on theplains were examined and determined mainly concerningnine items including the effects on living organism,fishing and tourism, these items were limited to two items
which are effects on living organisms and landscapes,
considering the characteristics of mountainous rivers.
Concerning the effects on living organism, we decided
to determine the minimum water level by modeling thestructures peculiar to mountainous rivers such as a riffle,
a pool, and a step-pool for hydraulic calculation andverifying changes in water level of the river channel
depending on flow condition by model calculation. For
building the model and grasping the effects on livingorganism, we conducted a field study on rivers.
Concerning the effects on landscape, we went back to
the elements relating to landscape peculiar tomountainous rivers in this examination, although it isconsidered to be suitable for flow demand as an indicatorin the existing method for rivers on the plains that thewidth of water surface of a river should be equivalent to
20% of the width of the river. In a questionnaire usingphotographs showing flow conditions of mountainous
rivers, we investigated in which parts of the photographs
people feel the volume of water, and it was found thatmost people feel it in whitened parts of ruffling surface
arising from drops and other in these flow ofmountainous rivers. For that reason, we grasped therelation between the occurrences of ruffling surface andthe physical conditions of rivers through this survey andexamined for indexing.
3. Future plans
Together with these survey results, we will arrange theresults of examinations at the time of implementingexisting hydroelectric power and organize the way of
thinking the flow demand of mountainous rivers,
exchange opinions with scholars based on examinedknowledge to conduct water utilization investigationsmoothly, and put them together as indicators for water
utilization investigation.