二∴．．‥
G． ぴ−，32，419（1951）．
（229）福島久雄：河口二重水屑における渦動拡散につ いて，北海道大学工学部研究報告，（．12），（195S）一．
（230）市栄誉：Estuaryの水理について，海岸工学 講演会講演集，（1955）．
（231）吉良八郎，玉井佐一・：貯水池の滞砂に関する研 究から（5，6），土地改良，8（12），45〜54
（1958），9（勿，32〜44（1959）．
（232）BROOKS，F。A‖，BERGGREN．W．P．：Analyti−
Calinterpretation of den＄ity currents o董 air chilled by nocturalradiation，Trans．，
A＝G‖打，24，189（1943）．
（233）吉良八郎：かんがい用貯水池の滞砂に関する研 究（6），香川大学農学部学術報告，9（2），79〜93
（1957），
（234）舌良八郎：かんがい用貯水池の滞砂に関する研 究（7），香川大学農学部学術報告，9（8），171〜194
（1958）．．
（235）吉良八郎，かんがい用貯他の滞妙に関する研究
（軌香川大学農学部学術学術報菖10（1），51〜73
（1959）．
（236）吉良八郎：かんがい用貯水池の滞妙に関する研
究（10），香川大学学術報告，11，111〜137（1959）．．
（237）NIZERY，A。，BoNNIN，J．，：Obser・Vation SyStematique de caurant de densit6dans
une retenue hydr・Oelectrique，Proc．、Minn…
ム祓狩猟．だ加わ．Cの砂励融‰明，369（1953）．．
（238）石原藤次郎，本間仁編：応用水理学（中∬），
338（1958）．
（239）MuNK，W且，and ANDERSON，E．R ：Notes On a theory of the ther・mOClirle，J肋r 足紺．．，7，276〜295（1948），．
（240）ERTEL，HB．：Theorie der・thermischen Sprungschichtin Seen，Acla。HydrophγS．り
1，151（1954）
（241）川原琢磨：潅漑水温上昇に関する基礎研究（Ⅰ，
Ⅱ），農業土木研究，21㈲，（1953），22（1），（1954）
（242）吉村信書：東亜の陸水（太平洋の海洋と陸水），
太平洋協会編，60（1942）
（243）小島貞雄：貯水池の湖沼学的研究（Ⅰ），水道協 会雑誌，（165），13（1948）
（244）田中治雄：三浦貯水池における水没年変化につ いて，電力技研報‖，土木＝軋（1950）い
（245）西条八束：湖沼における物質代謝の化学的研究
（Ⅳ），日本化学難語，77（6），（ユ956）．
（246）川原琢磨，伊藤兼松：伊藤式表層水吸込取水装 置による表層水の取水について，水温の研究，1 匝），（195フ）‖
（247）BouNEFILLE，R‖：Etude exper・imentalde I′influence dela董orce de Coriolis sur1a propagation deユa mar 6e danslaManche，
ム2月加妬偵＝郡毎鮮血，12−β，667（1957）．
（248）TAKANO，K。：A complementary note on
the diffusion of the seaward river fユow
Off tbe mouth，∫0〟γいOcβd．5∂C．．′（ゆβ乃，11佳），
147（1955）
（249）本間仁：河川攣曲部における水流について，土 木試験所報告，（：32），67（1935），
（250）向井正幸：青木湖における湖水清澄度の鉛直分 布並にその変化について（1，2），気象発話，T9
（6），（1941），21（6），（1943）
（251）MUKAI，M ：The stagnant turbidlayer
developedin the thermocline oflake
Aokiand Noziri，Jbur．Pbculiy ofLiberal A再・5の加㌧釦鹿川呵∴鋸め・Sゐ〝ぴ〃まび小，2，（1952）
（252）向井正幸：木崎湖における湖水清澄魔の鉛直分 並．にその変化について，気象集誌，19牲），（1941）．．
（253）向井正幸：野尻湖にLおける湖水清澄魔の鉛直分 布，気象集誌，20（12），（1942），
（254）MUKAIM，：The stagnantturbidlayerde−
Velopedin the thermocline oflakeNoziri，
．わ〝γり 釣c〝g〜ク q／ ヱま∂βγαg A7ね d乃dぶc吉♂乃C♂，
Sカ言がゐ加び乃古び，．，6，（1956）
（255）関口嘘書，朝比奈貞．一▲，北岡轟海：河口湖およ び西湖の水質に関する光学並に化学的検査，気象 集誌，14（5），（1936）
（256）TAl柑MURA，T．：A modelexperiment re−
−177−
Lerring to the cause of the formation of
the turbidlayerin thelake，Pbculty
エ詑昭れが．4れSの由㌧凱去♂押C♂，Sゐgがゐ〟 打得ね．，（5），
（1655）．
（257）安井善一・：海水の透明度と雲量および雲形との 関係について，海洋気象台粂報，（78），（1935）．
（258）宇田道隆：日本近海における水色透明度の分布 状態およびその年変化，海と窒，10（軌（1932）．．
（259）前川忠夫かんがい用貯水池相に関する研究
（水位，水温および透明度について），香川大学 農学部学術報告，8（1），44〜56（1956）．．
（260）有泉島 牧陸生：酸性河川の水質に関する研究
（1），建設省土木研究所報告，（88−6），（ユ954）一′
（261）根来健一・朗：琵琶湖の水質，陸水学会誌，19（1），
（1957）
（262）MORT‡MER，C．打，．：The exchange of diso−
1ved substances between mud and waterI inlakes，／い丘C〃J．，30，（1941）い
（2（i3）太田頻敏，橋本湯之助．．かんがい用貯水池の水 質に関する調査研究（1），奈良学芸大学紀要，7（2），
（1957）い
（264）玉置鷹彦，星川玄児：池泥の研究（ユ〜4），香 川大学農学部学術報告，5（2），（1953），8（到，
（1954），8（凱（1957）．．
（265）前川忠夫：かんがい用貯水池将に関する研究
（池水の肥効質について）香川大学農学部学術報 告，1l，89〜98（1959）．
（266）香川県農業試験場編：農業図説，（ユ955）．
（267）佐藤清一・，吉川秀夫，芦田和男：河川の土砂流 送に関する研究，土木研究所報告，（101−3），
（1958）．
（268）吉良八郎：貯水池に・おける飽水の流動と水質分 和こついて，香川大学農学部学術報告，12（1），52
〜63（1960）．．
（269）小島貞男：貯水池における水の流動について，
水道研究，（40），（1960）い
（2フ0）香川県河川課：内場池管理年表，（1954，1955）
（271）小島貞男：貯水池における浮遊沈降機構の一考 察，第24回陸水学会大会講演要旨，（1959）．
（272）志村博康：滑れの一・定応力層における
RIC王王ARDSON criterion，昭和34年度農業土木学 会大会講演会要旨，15〜17（1959）
HydraulicalStudies on the Sedimentationin Reservoirs Hachir8KIRA
R杏sum香
ChapterI．ImかodⅦetion
Mostimpounding r・eSerVOirs are constructed for power，irrigation，flood control，Water Supply・
recr・eation，breeding or multiple purposeslOne olthe chief problemsin the operation and
maintenance of the reservoirsis theloss of water storage resulting from the accumulation of
sediment。Damages may thus be said to startwith the beginningOf stor・age and sedimentation・Sedimentation damages a reser・VOir whenit reduces the storage capacity to the point where the reservoirCannOt Supply the 董ullsurvices for whichit was designed。Itisinevitable，in most
cases，that the usefulstorage capacity behind a dam willbe reducedin time by sediment
accumulation untilreplacement storageis necessary．This sediment accumulation，in turn，
influences the design of the dam because of the e董fect on active storage capacity requirements，
outlet sillelevations，Sedimentary pressures，reCreationalfacilities，SCOuring Sluice，breeding facilities，and back・Water COnditionsh Deposition above the reservoir causes swamping and董100d・
ing by back，Water effectsin the valley
Many reSerVOirsin our country constr・uCted years ago have become completely filled with
sediment deposits resultingin practicaluselessness．Various methods have been suggeSted
and tried for・remOVing，reducing，Or by−paSSing sediments．Although none has yet supplied us with a solution，particularlyinlarge reSerVOirs，perhaps some day when the need becomes
acute a method willevolve．The mostlasting solution of the problemis reduction of the rate
of sediment production from the contributing drainage area，prOVided that the reservoiris an
efficient sediment trap and that sedimentation has not already progressed to the point wher ethe reservoir would be useless before effective measures could be carried out on the watershed
A good vegetalcover on a watershedis the best pr・eVentive of sedimentation，andit assur eSlonglife for a rIeSerVOir．The sources of sediment must always bedeterminedbeforeaneffective
water・Shed−treatment PrOgram Can be plannedChapterI‖0王Ithe S七ate of Reduction of Storag■e Capaci七y
Due to Deposition of Silt and Problems of Controlling
Silt DepositioninJapan
The depletion of storagein reservoirs due to the deposition of siltis an economic problem
that cannot beignoredin the design of such structures．．The most recent reservoir sediment
data have been analyzedin thisitem on the state of reduction oIstorage capacity due to depo−
Sition of silt and problems of contr・011ing silt depositionin our countr・y The results are summarized aslollows：
（T）Generally speaking various changes have been acknowledged concerning the state of silt
deposition of256reservoirslor powergenerationinJapan，the reason of which was attributed
to the multiple cor・relativein王1uence of every Lactor−S havinglarge effect upon the depositions，
but the annualmean silt deposition rate rs（％）isl．8870n an aVerage，and the totalsilt depo−
sition r・ate Rs（％）is as follows：Rs＞100％（5 reservoirs），Rs＞80％（26reservoirs），R＄＞50％（56 reservoirs），Rs＞10％（159r・eSerVOirs）and Rs＜0％（5 reser・VOirs）
−178−
And for・the annualmean silt deposition rate rs（％）concerning93r・eSer・VOir・Sin U．S．A．is O．729 on an average，and the totalsilt deposition rate Rg（％）conserning62reservoirsis as follows：
Rs＞50％（2 reservoirs）and Rs＞10％（25reserviorsl）
（2）various methods of controlling silt depositionin reservoirs may be dividedintofour
generalclasses，（1）properSelection of the reSerVOir site and design features of the dam and r・eSerVOir，（2）conservation and management of the watershed，（3）contr・Olof sedimentinflow，
and（4）r・emOValand utilization of sediment deposits
Such being the case，itis quite promising that the effect of controllinq silt deposition shows quite str ikingly by the sand・drainage method by turbidity density cur rent，Sand trap method by Slit conduit or vortex tube and sand trap method for mud mixing of arableland by silt pump
Chapter u．On the Mechanism that Reservoirs WillBe Filled with Sediment
One o董the chief problemsin the operation and maintenance of the reservoiris theloss of
Water StOrage reSultinglrom the accumulation of sediment‖For the proper solution of these pro−
blems，aCknowledgment of the pr・inciples of which silt willfillup a reservoiris olten necessary In order to study the silt problems of reservoir，the authorinvestigated on the various factors
influencingthe sedimentationin reservoirs，On the problems of transpor・tation of sediment above the reservoirs，and on the problems of deposition of sedimentin the reservoirs
The results are summarized as follows：
（1）The major factors thatinfluence sedimentationin reservoirs are（1）watershed area，但）
SOilproperties，（3）topogr・aphic characteristics，（4）properties of the vegetative cover，（5）climatic CharaCteristics，（6）hydr・aulic propertiesin the stream，（7）human factors，（8）envir・Onmentalor positionalcoditions of the reservoir・Site，（9）stor・age CapaCity，（10reservoir shape，㈹hydraulical pr．opertiesin the reservoirs，岬variations of the storage waterlevel，a3）charcteristics of the Sedimentinflow，and（14）methos of contro11ing silt deposisionin the reservoirs
Nevertheless，Sedimentationin the reservoirsis an explicitlunction oltheindependent var・ia−
bles cited；mOreOVer，diHerent factors areimplicitly r・elated
（2）Itis clear that a complete solution of the silt problemsin reservoirs depend upon an evaluation of each of the variables with rIeSpeCt tO eaCh other．，Knowledge about the nature of Sedimentation as wellas effective controlmethodsin the reservoirs can be advarlCed only by
investigating theinterrelationships o董the factor・S mentioned
（3）Sedimentationin the reservoirs consists of fundamentalprocesses：（1）weather・ing，
（2）water erosion of theiand surlace，（3）tr・anSpOrtation by the streams，匪）depositionin the reservoirs，and（5）beach erosion by the wave motion。Most of the constituent particles of sedi−
ment＄in r・eSerVOirs are derived 董rom rocks or earth materials that have been more orless weathered
Both mechanicaland chemicalprocesses cause er OSion．Because of the close r・elationship amo−
ng er・OSion，tranSpOr・tation，and deposition，itis convenient to discuss the mechanicalaspects of these subjects in sequence and then take up chemical weathering and solution
（4）practically allstream−borne sediment comeslrom one or more of thelollowing sources：
（1）sheet erosion，rillerosion and gully erosion of theland surface，（2）fluvialerosionin the Str・eam，（8）mass movement（theseincludeland，Slides，Slumps，advances，SOilcreep，etC．），and 仕）董lood er・OSion．
（5）Both tractionaland suspensionalprocesses cause transpor・tationin the streams and sedi−
−179一
mentationin the r・eSerVOirs With water，the principalfactor・S that affect trIanSpOrt are：turbu−
1ence；Settling velocity；Shape，Size，density，and quantity of particles；mOVement along the bottom by saltation，r011ing；and turbidity density undertlow
（6）such being the case，itis quiteimportant problems that theinvestigation for・density curr・ent and beach er・OSion of reservoirsin our・COuntry
（7）In the orchard ofthe AgriculturalScience ResearchInstitute of Sloping Land which was established at the end ofユ952and belongs to the Kagawa UniverSity the5experimentalplots
warIe madeinJuly1954．The results from August，1954toJuly，1956are summarized follows：
1）The run−Off amountin every plot and eroded amountin tr・ee−CrOWn COVered plot have a Close connection to r・a王nfallbut the eroded amountin rluded pIot has a cIose connection to rainfallintensity
2）In every plot rainfallintensity and eroded soilhas a relation o董an exponentialcurve which is expressed by Es＝aZわ，Where Z：daily maximum 王ntensity of rainfall（mm／ユ0min），Esニeroded SOil（g／plot）and a and b：constants
3）As the soilerosion due to the rain was quite different by theinfluence of such variable
factors as climate，tOpOgraphy，Vegetatioll，SOiletc，the author fouzld that these e文王sted double COrrelation of a greaterdominance among suchitems as rainfall，rainfallintensity and eroded
SOil…And a more reliable theoreticalvalueis shown by the following empir．ical董ormula：
丘β＝刑佗
where Es：erOded soil（ton／ha），P：rainfall（mm／day），Z；daily maximumintensity o董rainfall
（mm／hr）and a＝0，000035，m＝1，52，n＝1い71：COnStantSin case of plot 5（inclination of15O，
standard nuded plot）
4）The criticalrainfallintensity of the dangerous rainsin nuded area of weathered granite
having aninclination of150and a soilnature whichis subject to er・OSionis considered to be 2mm／10minwith an allowance of the safety factor to be counter measure of soilconservation
Andin case a cultivatedlandis protected by coverinq（
etc。）and ter・racing，a tendencyis acknowledged that the standard criticalintensity wi11 increase
5）Soilconservation e董fectis shon quite strikingly by the covering with tree−CrOWn Of frout・treeS and grass mulch，And from the viewpoint of soilconservation the method of bench terraCingis more effective than that of contour planting in order to prevent erosion for the reclamation on slopes
It may be posible thatin both the experimentalplots before and a董ter the reclamation the run・Off of rainfalland the soilerosion due to reclamation willnot be expedited，Or eVen the reduction may be possible，in case thelandis covered by the tree−Cr・OWn Or・Other・SOilcover−
i明（grass mulch，COVer・−CrOpS etC．）and appropriate soilconservation farming orengineer・ingis taken after・r・eClamation
ChapterⅣ．．A Method of Estimating■the Life of Reservoirs by the Rates of Sediment Accumulation
From the viewpoint of maintenance and development of a reservoir，the reduction of stor・age CapaCity due to deposition of siltis counted as one of the mostimportant prObユems of a rIeSer−
VOir、The author has proposed a methad by which the silt deposition r・ate may be estimated on the basis o董 the data concerning the silt deposition observed at the sites of r・eSer・VOirsin our
country and foreign countries（chiefエy US．A。），and further，treated var・iotlS prOblems estimatin官
−180−
thelife of reservoirs The r・eSults are summarized as follows：
（7）Generally speaking various chanqes have beenacknowledged concerning the state ofsilt
deposition o董256reservoirs for power generationinJapan，ranging from Hokkaid6 to Kyasha district，the reason of which was attributed to the multiple correlativeinfluence of every
factors having1arge effect upon the depositions，but theannualmean silt deposition rate rs（％）
isl。8870n an aVer・ageThe above result shows that a r・eSer・VOir willbe filled up by the siltin about50years on an average
（2）And differences are seenin regions，river systems，etC．，for example，the rIateS rs at
reservoirsin the HiirIiverSyStemin Chagoku district andJintsム and Kurobe river systemsin
Chabu district averages over・5％
（3）The data concerning annualsiユt depositior10bserved at the sites reservoirsin our
countrIy have been classifified to develop 3 type curves of the r・elation be tween timein years since construction（Y）and annualsilt deposition rate（Rg）．The generalclassification resulting from the analysis of the data from the reservoirs董or power qenerationin our countryis as 董ol−
low：
C／㍑−C／′悟ミi托‡誓・霊諾VOi・r
。Annual mean silt deposition rate7s（％）
Reservoir type
TypeI（Reser・VOir・S Willbe hilled upin slack velocity）
Type Ⅱ（Reservoirswi11be hilled upinintermediate velocity）
Type Ⅲ（Reservoirswi11be hilled upin rapid velooity）
1＞
About 2〜3
く5
Down stream reseI−VOlr
Mid・Stream reSerVOir
Upstream reser voir Large
Medium Small
（4）The relation between capacity−CatChment area r・atio（C／F）and annualmean silt deposition
rate（Yg）concerning 316 reservoirs（223inJapan，90in US．A。，and 3in Taiwan）is shown by the followingempirical董ormula：
ダざ＝0．140（C／F）￣0420
where y＄：annualmean silt deposition rate（％），C：Originalstorage capacity of reservoir（m8），
and F：CatChment area of reSerVOir（m2）．．
（5）The relation between capacity−inflow ratio（C〝）and annualmearlSilt depositiorlrate（Ys）
concernig146reservoirs（106inJapan，39in U‖SAリandlin Taiwan）is shown by the following
empir・icalfor−mllユa：
グβ＝0小214（C／∫）￣04柑
where ys：annualmean silt deposion rate（％），C：Originalstorage capacity of reservoir（m8），
and Z：yearly meaninflow flowinqinto reservoir（m8）．In this case alar・gerinverse correlation is acknowledged than the cases o董C／Fratio
The maximum and minimum values of rs in this case are given by the following empirical
王ormulas，butitis considered that ysmiYiis not soimportant as Y8maガグsmα∬＝0一．920（q〝）−＝7き γs川名循＝0．0076（C／∫）￣0478
（6）The author obtained the followirlg emPiricalformuユas whjch give the average number of years（Y；）dur・ing which siltwi11fillup a r・eservOir
i㌔＝フ14（C／ダ）0420 坑＝467（C／∫）04i3
−181−