Residual Current System in Kii Channel in August 1996

農業土木学会論文集研究論文 Trans. of J S I D R E No.194, pp.87～96 (1998. 4)

Masayuki FUJIHARA*, Tateki FUJIWARA**and Gyozo OHASHI*

*C ollegeof Agriculture, Ehime University (3-5-7 Tarumi, Matsuyama, Ehime 790, JAPAN) **G raduateSchool of Agriculture, Kyoto University (Sakyou-ku, Kyoto 606-01, JAPAN)

Abstract Residual current in Kii Channel in August 1996 was simulated by using a robust diagnostic numerical model. The computed

results were verified by an Acoustic Doppler Current Profiler (ADCP) data obtained along the two observational lines.

The computed residual current is as follows. From the water surface to the depth of 30m, the water coming from Osaka Bay

flows southward to the line of 34•‹ N and veers to the west because of the existence of the counterclockwise eddy in the central part of

Kii Channel. After the changing of its direction, the water flows southward along the Shikoku island. The water again changes its

direction to the east off Man City and approaches the Kii Peninsula, then flows out to the Pacific Ocean along the Kii Peninsula. As a

whole, the southward current is apparent in this layer. Below the depth of 50m, the northward current is dominant as a whole . The forcing balances among the terms in momentum equation were investigated. The tidal stress balances with the pressure

gradient around the strait. In other regions, the tidal stress is relatively small. Main balance is established between the pressure gradient

force and the Coriolis force in Kii channel. Therefore the residual current in Kii Channel is supposed to be geostrophic .

Key words: Residual current, Diagnostic model, Kii Channel, Geostrophic current, Density current, Tidal stress

1. INTRODUCTION Therefore a diagnostic model, which gives the flow field from the observed density field, is suitable to compute the Kii Channel surrounded by Kii Peninsula, Shikoku residual current in Kii Channel. Island and Awaji Island opens to the Pacific Ocean and In view of verification, the water temperature and connects with Osaka Bay through Kitan Strait and with salinity data recorded simultaneously with the current the Harima-Nada sea through Naruto Strait. Because of data are preferable. Fujiwara, one of the authors, difficulty of setting moored current meters, characters of measured current velocities, water temperature, salinity residual currents in Kii Channel have not been known and nutrients along two cross-sections on 6-8 August yet. 1996(not published). The current was measured by an On the other hand, it was reported that nutrients are Acoustic Doppler Current Profiler (ADCP), thus the transported from the inner shelf to Kii Channel during distribution of residual currents in two vertical planes the summer (Fujiwara et al., 1997). This could be one were obtained in detail. The three Prefectural Fisheries reason why the water quality in Osaka Bay, especially Experimental Stations also measured water temperature offshore region has not been restored, though the and salinity in and around Kii Channel when the above terrestrial nutrients loading has been reduced. Long-term field observation was carried out. Therefore we obtained transport of substance such as nutrients is mainly affected synoptic data set, which is suitable for a verification of by Residual Current(RC) in coastal waters. In this way, computational results. the residual current in Kii Channel also has an important This paper aims to know the RC distribution in Kii meaning from the point of water quality in Osaka Bay. Channel in the August by developing a multi-level robust To the authors' knowledge, a three-dimensional diagnostic numerical model and resorting it. numerical simulation about the residual current system in Kii Channel has not been conducted. 2. MODEL DESCRIPTION In Kii Channel, water temperature and salinity have been measured at many fixed stations once a month by 2.1 Basic equations three prefectural fisheries experimental stations. A multi-level robust diagnostic numerical model

農土論集 194 (66-2) 283 88 農業土木学会論文集第194号(第66巻第2号) presently employed is represented by the momentum the prescribed cell-density calculated from observed equation of the RC including the tidal stress on the values, u(u, v) the horizontally two-dimensional M2 tidal rotating earth accepting f-plane approximation, the current vector, w the vertical M2 tidal current velocity, t continuity equation and the density transport equation the time, z the vertical coordinate positive upward, and

(Fujihara and Kawachi, 1995b); the over-bar in Eq.(6) denotes time average over one tidal

cycle. The last term on the right-hand side of Eq.(5),

called ƒÁ-term, is that introduced by Sarmiento and

Bryan (1982) to prevent computed density from deviating (1) greatly from the corresponding prescribed cell-density ρOB・This term plays a role of artificial source/sink of density to converge computed densities to prescribed ones. Special treatments for boundary conditions are not (2) necessary in solving the density transport equation Eq.(5), because all the density values along the exterior boundaries are also given in advance. Boundary (3) conditions for the momentum equation Eq.(1) are expressed as ; at the free surface,

(4)

(8)

(5) where, pa is the atmospheric density (=1.23kg/m3),

γ2a the drag coefficient of free surface (=0.0013), and Ww the horizontally two-dimensional wind vector, at the sea bottom, (6)

(9)

(7)

where, ƒÁ2b is the frictional coefficient of bottom

(=0.0026), where, U(U, V) is the horizontally two-dimensional and at the land boundary, velocity vector of residual current, W the vertical component of residual current, V h the horizontal (10) differential operator, f Coriolis parameter, k the locally vertical unit vector, p the pressure, vh,vv the kinematic which is the no-slip condition. eddy viscosity coefficients in the horizontal and vertical Prior to operation of the diagnostic model, the tidal respectively, L the tidal stress, g the gravitational stress Ts is computed through tidal current simulation acceleration, ƒÅ the sea surface elevation above the mean under the barotropic flow condition in the area which sea level, H the water depth, p the water density, Kh, Kv encompasses Kii Channel. the turbulent diffusion coefficients in the horizontal and The value of vh is changed proportionally to the vertical respectively, y the inverse time constant, ƒÏob square of the amplitude of tidal current variations, in the

284 Trans. JSIDRE Apr. 1998 Residual Current System in Kii Channel in August 1996 89

same manner ( vh = 0.016 •E Tp •E u2am, ; Tp = tidal period, uam latitude 33•‹ 42'N and 34•‹ 25'N which encompass the

= amplitude of tidal current) as in the previous work by southern part of Osaka Bay and that of the Harima-Nada

sea and Kii Channel, as shown in Fig.1. The whole body Fujihara and Kawachi (1995a). Thus the resulting vh - of water is discretized into 1km •~ 1km square meshes values are 800m2/s in Naruto Strait and 300m2/s in Kitan horizontally and ten levels vertically ( 1 st level : 0-2m, Strait, while these values are about 1m2/s in zones where 2nd level : 2-5m, 3rd level : 5-10m, 4th level : 10-20m , tidal current is weak. The value of v, generally depends 5th level 20-30m, 6th level : 30-40m, 7th level : 40-50m, on the strength of stratification that is closely related to 8th level : 50-75m, 9th level : 75-100m, 10th level : the tidal current intensity. Therefore the vv -value is set 100m-bottom) in order to employ the finite difference to a hundred-thousandth of vh -value. Thereby it takes numerical method.

80cm2/s at the Naruto Strait and lcm2/s as a minimum. 2.3 Distribution of density The values of K,, and IC, are set to 1m2/s and 1 cm2/s , The model used in this study requires the data of respectively. density, wind stress and tidal stress as the input data at Equation (1) is integrated in time by using the same each computational cell. At first, we describe the method numerical scheme as in the previous work (Fujihara and to estimate the density distribution. The observation Kawachi, 1995b), until steady state solutions of the RC stations of Wakayama, Osaka and Tokushima Prefectural are obtained. For successful correction of cell-densities, Fisheries Experimental Stations are also shown in Fig.1. the coefficient y is now set to 0.5/ At (ƒ¢t = 30sec ) At individual locations, water temperature, salinity that intermediately underrelaxes the correction , etc. have been measured at several depths once a month. (ƒÏob-ƒÏ). Moreover the intensive observation mentioned before was

carried out from 6th to 8th in August 1996. 2.2 Study area In this study, the water temperature and salinity data The area under consideration is that lying between obtained from 1st to 9th in August 1996 by three

Fig.1 Bottom topography of study area and observation stations of density (•œ) and wind (•›). Numerals show the depth in meter.

農土論集194(66-2) 285 90 農業土木学会論文集第194号(第66巻第2号)

prefectural fisheries experimental stations and those obtained from the intensive observation were used to estimate the density distribution in Kii Channel.

For estimating cell-densities from the scattered densities obtained, interpolation and smoothing techniques are employed. Firstly, level-densities (ƒÏot) at an observation station (i) are determined by the linear interpolation from the measured densities. Secondly, interpolated cell-densities (pc,b) are estimated by using the expression;

(11)

where L is the distance to the observation station (i) from Fig.2(a) Interpolated density distribution(ƒÐt) in Kii Channel from the cell under consideration and n the number of surface to the deth of 2m. observation stations used to estimate the cell-density. We assume that the cell-density is affected by all the observed data within the distance of 6km from the cell. When less than three stations are found in that area, the distance is increased by steps of 1 km until three or more stations are involved in the circle. This means that the value of n in

Eq.(11) should be greater than 2. Equation(11) assumes that the effect of each observed data is inversely proportional to the distance from the cell to the observation stations. Finally, in order to smooth the density field, the cell-densities are averaged over a centered cell and adjoining 8 cells.

The resulting respective density fields are shown in

Fig.2(a)•`(e). The lighter water exists in the central part Fig.2(b) Interpolated density distribution(ƒÐt) in Kii Channel from of Kii Channel, at the mouths of Yoshino River and the depth of 5m to 10m. Kinokawa River in the surface layer. The water mass in the central part of Kii Channel is lighter than those in inner part of the channel and near Pacific Ocean in the upper layer (•ƒ20m). Below the depth of 20m, the heavier water, which corresponds to the cool water mass, exists off Yura Town.

Though we do not show the figures, the distributions of water temperature and salinity, from which the density is calculated, are as follows; from the sea surface to the depth of 10m, warm water (•„28•Ž) exists along Kii

Peninsula and cooler water (•ƒ27•Ž), extends along the

Shikoku island from the Naruto Strait . This low temperature in the surface is a result of vigorous tidal mixing at the Naruto Strait. In the other words, the water in the east-half of Kii Channel is warmer than that in the Fig.2(c) Interpolated density distribution(ƒÐt) in Kii Channel from the depth of 20m to 30m. west-half. Below the depth of 20m, tha cool core exists in

286 Trans, JSIDRE Apr. 1998 Residual Current Systemin Kii Channel in August 1996 91

Fig.2(d) Interpolated density distribution(ƒÐt) in Kii Channel from

the depth of 40m to 50m. Fig.3 Interpolated wind velocity field over Kii Channel during 6-8 in August 1996.

in August, 1996, using the objective interpolation method

previously described (same as Eq.(11)). Here, the observed wind vectors are doubled, because the wind

speed over the sea is generally about twice as much as

that over the land (Shimizu and Isoda, 1997).

Figure 3 shows the distribution of interpolated wind

vectors. The wind over the western and eastern parts of

Kii Channel is blowing from the south and south-west,

respectively. The wind speed is about 5m/s all over Kii

Channel.

2.5 Distribution of tidal stress

Fig.2(e) Interpolated density distribution(ƒÐt) in Kii Channel from The tidal stress distribution was obtained from the

the depth of 50m to 75m. results of tidal current simulation under barotropic

condition via Eq.(6). The tidal current simulation was the center of the channel. Next about the salinity conducted in the area lying between latitude 134•‹20'E distribution, less saline water influenced by the discharge (western open boundary line) and 33•‹40•‹N (southern of Yoshino River exists along the Shikoku island and open boundary line) which fully encompasses the study saltier water along the Kii Peninsula from the sea surface area. The western open boundary line is divided into two to the depth of 30m. Below the depth of 30m, the water is due to the existence of Syodo Island. Since the M2 tide is homogeneous in salinity. most dominant in this area, only the M2 tide was

considered to drive the tidal current. As to the boundary 2.4 Distribution of wind stress conditions, the amplitude (A) and the phase lag (ƒÖ) of Around Kii Channel, hourly variations of the wind the M2 tide, were given along the open boundary lines speed and direction are measured at eight stations (A=0.4m, ƒÖ=322•‹ along the western boundary north of (Tokushima, Gamouda, Hiwasa, Wakayama, Goboh, Shirahama, Sumoto and Nandan) by the Automated Syodo Island : A=0.4m, (0 =325•‹ along the western Meteorological Data Acquisition System (AMeDAS), the boundary south of Syodo Island : A=0.45m, ƒÖ=175•‹ Meteorological Agency (see Fig.1). along the southern boundary). We estimate the distribution of wind vectors over the Figure 4 shows the tidal stress distribution in the Kii Channel from the wind data measured from 6th to 8th surface layer. The computed tidal stress are so small

農土論集194(66-2) 287 92 農業土木学会論文集第194号(第66巻第2号)

FIg.4 Computed tidal stress distribution in the surface layer. Fig.5(a) Computed residual current from the surface to the

depth of 2m. A star (•š) denotes the center of the eddy. except in and around Naruto Strait (max=0.04cm/s2) and

Kitan Strait (max=0.01cm/s2). In other layers, the tendency is the same as shown in Fig.4.

3. RESULTS

3.1 Residual current

The computed results for the respective levels are

depicted in Fig.5(a)•`(h). The current patterns in

Fig.5(a)•`(e) (from the surface to the depth of 30m) are

nearly the same. Hereafter we refer to the layer from the

surface to the depth of 30m as the upper layer. The major

flow pattern in the upper layer is as follows. The water

coming from Osaka Bay through Kitan Strait flows Fig.5(b) Computed residual current from the depth of 2m to southward to the line of 34•‹ N and veers to the west 5m.

because of the existence of the counterclockwise eddy in

the central part of Kii Channel. The center of this eddy is

indicated by a star (•š) in Fig.5(a). After the changing of

its direction, the water flows southward along the

Shikoku island. The water again changes its direction to

the east of Anan City and approaches the Kii Peninsula,

then flows out to the Pacific Ocean along the Kii

Peninsula. As a whole, the southward current is apparent

in the upper layer. The main hydraulic characters

depicted in Fig.5(1) and (g) are almost same. We refer to

this layer (from the depth of 30m to 50m) as the middle

layer. The counterclockwise eddy mentioned before still

exists in the central part of the channel and the water,

north of the vortex, flows northward, i.s. toward Osaka Fig.5(c) Computed residual current from the depth of 5m to Bay along Awaji Island in the middle layer. Below the 10m.

288 Trans. JSIDRE Apr, 1998 Residual Current System in Kii Channel in August 1996 93

Fig.5(d) Computed residual current from the depth of 10m to 20m . Fig.5(g) Computed residual current from the depth of 40m to 50m.

Fig.5(e) Computed residual current from the depth of 20m to 30m. Fig.5(h) Computed residual current from the depth of 50m to 75m.

depth of 50m (lower layer) , the northward current is dominant as a whole (Fig.5(h)). Figure 6 shows the residual current profile in the Kitan Strait. The water from surface to the depth of 35m flows southward and below that the countercurrent exists.

3.2 Forcing balances Since the computed results described above are in steady states, the time variation term in Eq.(1) is equal to zero and the other terms should balance with each other. The distributions of the terms in Eq.(1) along the two lines shown in Fig.7(a) are depicted in Fig.7 (b) and (c). Figure 7(b) shows the forcing balances in y-direction

Fig.5(1) Computed residual current from the depth of 30m to 40m, along the north-south line through'Kitan Strait (J=78) at the depth of 7.5m. It can be seen that the tidal stress

農土論集194(66-2) 289 94 農業土木学会論文集第194号(第66巻第2号)

balances with the pressure gradient around Kitan Strait and the diffusion term balances with the pressure gradient in Kitan Strait. In other regions, the tidal stress is relatively small. Main balance is established between the pressure gradient force and the Coriolis force in Kii channel. Figure 7(c) shows the forcing balances in x- direction along the east-west line at the depth of 7.5m. It can be easily seen that the pressure gradient term balances with the Coriolis force almost all over the line. As a first approximation in Kii Channel, the pressure gradient term balances with the Coriolis force. Therefore the current in Kfi Channel is supposed to be geostrophic.

4. DISCUSSIONS

The residual currents were calculated from the current data measured with ADCP for 25 hours during three days from 6th to 8th August 1996 (Fig.8(a)-(c)). Figure 8(a) shows that the water at the south part of the Kitan Strait Fig.6 Residual current profile in the Kitan Strait.

(a)

(b)

(c) Fig.7 Forcing balances: (a)North-south and east-west lines, along which the forcing balance in the momentumequation are calculated. (b) Forcing balance of y-direction along the north-south line. (c) Forcing balance of x-direction along the east-west line.

290 Trans. JSIDRE Apr, 1998 ResidualCurrentSysteminKiiChannelinAugust1996 95

Fig.8(a) Observed residual current at the depth of 10m during 6-8 Fig.9(a) Computed residual current picked up along the observed August 1996. lines at the depth of 10m.

Fig.8(b) Observed residual current at the depth of 30m during 6-8 Fig.9(b) Computed residual current picked up along the observed August 1996. lines at the depth of 30m.

Fig.11(c) Observed residual current at the depth of 50m during 6-8 Fig.9(c) Computed residual current picked up along the observed August 1996. lines at the depth of 50m. flows southward and veers to the west at the central part the northward current is prominent in the east part of the of Kii Channel and then flows southward in the west part channel and we can find out that the water at the depth of of Kii Channel. Figure 8(b) shows that the southward 50m flows toward the Osaka Bay (Fig.8(c)). These flow current is dominant in the west part of Kii Channel and patterns estimated from the ADCP data are almost same

農土論集194(66-2) 291 96 農業土木学会論文集第194号(第66巻第2号) as the computed flow patterns described above. To verified by the field data obtained with ADCP. The compare the computed results with the observed ones in agreement between the computed and observed currents detail, the computed velocity vectors picked out on the was fairly good. This is because we could obtain the same observed lines are shown in Fig.9(a)-(c). The density data recorded almost simultaneously with the computed results are in good agreement with the current data. Hence high quality data set guarantees that observed ones. If examined in detail, the difference the diagnostic model can precisely reproduce the current. between computed results and the observed ones is more To say this reverse, the accuracy of the diagnostic model apparent at the northern line than at the southern line. It depends on the reproducibility of density fields. is presumed that this difference is caused by the fact that the observed densities around the Kitan Strait are not the Acknowledgements : The authors wish to thank Wakayama, averaged values for 25 hours. The density distribution Tokushima and Osaka Prefectural Fisheries Experimental around the Kitan Strait is influenced significantly by the Stations for providing the data. tidal current and then the distribution changes REFERENCES corresponding to the phase of tide. However the density Fujihara, M. and Kawachi, T. (1995a) : Kinematic Eddy Viscosity we used in the computation was measured just one time. Coefficients in residual Current Equations with Tidal Stress, Trans. Therefore if we used the averaged values for 25 hours JSIDRE, No.176, pp.233-240 around the Kitan Strait, the computation results would Fujihara, M. and Kawachi, T. (1995b) : An Adaptation of Diagnostic Numerical Model of Residual Current to Bungo Channel, Japan, accord well with the observed ones. Moreover, to improve Trans. JSIDRE, No.180, pp.39-48 the accuracy of reproduction, the density in the Kitan Fujiwara, T., Uno, N., Tada, M., Nakatsuji, K., Kasai, A. and Sakamoto, Strait is needed., W.(1997) : Inflow of nitrogen and phosphorus from the ocean into the Seto Inland Sea, Proc. Coastal Engineering (JSCE), 44. (in printing). 5. CONCLUSIONS Sarmiento, J. L. and Bryan, K.-(1982) : An Ocean Transport Model for the North Atlantic, J. Geophys. Res., 87, No.C1, pp.394-408 Using the multi-level robust diagnostic numerical Shimizu, M. and Isoda, Y. (1997) : The Transport Process of Walleye model, the residual current in Kii Channel has been Pollock Eggs into Funka Bay in Wnter, Bull. Japanese Soc. Fisheries Oceanography, Vol.61, No.2, pp.134-143 (in Japanese computed and the results have revealed that the residual with English abstract) current in Kii Channel is quasi-geostrophic, except in 〔Received Sep.24,1997,Accepted Dec.1,1997〕 and around straits. The computed currents have been Questions and/or discussions on this paper for public 〔debate will be accepted before October 24, 1998. 〕

紀伊水道における1996年8月の残差流構造

藤原正幸*・藤原建紀**・大橋行三*

*愛媛大学農学部(〒790愛媛県松山市樽味3 ・5・7) **京都大学農学研究科(〒606 -01京都市左京区北白川追分町)

要旨診断モデルを用いて紀伊水道における1996年8月の残差流の実態を明らかにした.計算結果は,紀伊水道内の2測線で得られたADCPのデータによりその再現性を検証した,表層(30m以浅)では大阪湾より南下してきた流れが北緯34度付近に存在する反時計回りの渦により西に曲げられ四国沿いを南下し,阿南市沖で今度は流向を東に変え最終的に紀伊半島に沿って太平洋に流出する,全体としては南下流が卓越している。底層(50m以深)は全体として北上流が卓越している. 運動方程式の各項のバランスを計算すると,海峡部付近では潮汐応力と圧力勾配力が釣り合っている.他の海域で潮汐応力は小さく,圧力勾配力とコリオリカがバランスしている,このことから紀伊水道における残差流は地衡流的であると考えられる.

ヰーワード:残差流,診断モデル,紀伊水道,地衡流,密度流,潮汐広力

292 Trans. JSIDRE Apr. 1998 〔研究論文〕〔研究論文〕窒素投入に関するエネルギー消費・CO2排出不撹乱粘土の圧縮指数式についてのライフサイクル分析 ― リサイクル型農業の環境負荷に関する考察― 甲本達也・朴鐘華不撹乱粘土の圧縮指数Ccを,土の種類,土の状態および骨小林久組構造を表す指標として,塑性指数Ip,液性指数ILおよび鋭高投入型農業と地域資源リサイクル型農業の環境負荷の総合敏比Stを選び,IpおよびILのCcへの寄与効果を両者の積(Ip 的な検討を試みるために,エネルギー消費とCO2排出を環境 ×IL=w1-wp)で表すと,Ccは次式の関数形で与えられる。負荷項目として,農業における窒素投入のライフサイクル分析 Cc=F((w0-wp),St) を行った。分析範囲は,製造,輸送,廃棄段階を含む肥料投入ただし,w0およびwpは初期(圧密開始時)含水比および塑までの部分で,分析により窒素単位量当たりの各段階のエネル性限界時の含水比. ギー消費・CO2排出量を明らかにした. 不撹乱粘土試料に対して上式を適用したところ,かなり高いさらに,地域資源リサイクル型農業に対応する循環型シナリ相関係数のもとで次式が得られた. オとして畜産～農産連鎖モデルを作成し,これと高投入型農業 Cc/St0.22=0.009(w0-wp)+0.101(相関係数r=0.911) に該当する化学肥料依存型シナリオとのライフサイクル分析に Ccと練返し粘土の圧縮指数Cc'の比はCc'>0.4の範囲でよる比較を行った.その結果,CO2排出量は循環型の方がは,Cc/Cc'=1.25St0.22で与えられた. 3,373～4,183kg/ha少ないと試算されたが,エネルギー消費はキーワード圧縮指数,圧密試験,鋭敏比,不撹乱粘土,含水比,飽和粘土, 適用するコンポスト化技術の違いによって,循環型の方が大き間隙比,塑性限界な環境負荷を生じる場合のあることが推定された. (農土論集194,pp.59～63)

キーワードライフサイクルアセスメント(LCA),環境効率,CO2排出, リサイクル,窒素フロー,地域農業システム,コンポスト

(農土論集194,PP.51～57)

〔研究論文〕〔研究論文〕降雨条件下でのリル生成に関する実験的研究斜面における湛水発生時間と水分移動の数値シミュレーション (本文=英文) (本文=英文) Farmanullah KHAN・佐藤晃一・高瀬恵次朱敦発・中野政詩・宮焙毅

人工降雨装置を持つ2連のライシメータを用い,勾配を変化砂とYolo粘土を用いて,斜面における水移動の数値シミュさせて不等流条件下でのリル生成メカニズムについての実験をレーションを行った.第一に,湛水開始時間は,降雨強度の増行った,その結果,リルの生成過程は3つの段階一水みちへの加とともに指数関数的に減少する.斜面の傾斜角が30。以上に集中を伴う面状侵食,微小リル侵食およびそのリルの発達一かなると,土壌の浸潤能は平面と比べ著しく異なった.第二に, らなることが明らかとなった.このリルの発達が始まる斜面上斜面に平行な流れに対して土壌の物理的性質が大きく影響する端からの距離をリル生成の限界距離と定義してこれを測定し, ことが分かった.湛水開始の際砂の場合は浸潤前線の後方でまた,その地点での地表面流量を限界流量と定義して計算によ飽和層と不飽和層の区別が明確にできたが,粘土の場合にはでり求めた.そして,限界距離は降雨強度と勾配に依存するが, きなかった.第三に,斜面角度と降雨強度はフラックスの大き限界流量はそれぞれの勾配に対して一定であることを明らかにさ及び屈折を決定する重要な要素であることが分かった. した.次に,表面流が薄層流の流れであると仮定して限界流速キーワード降雨浸潤,湛水発生時問,斜面水流,フラックス屈折,傾斜角を求めた結果,土壌特性が一定であれば限界流量はいずれの勾 (農土論集194,pp.73～80) 配においても同じであると考えられることを指摘した.

キーワードリル生成,限界掃流力,不等流,雨水流法 (農土論集194,pp.65～71)

〔研究論文〕〔研究論文〕飽和一不飽和浸透流の不飽和特性と相似則紀伊水道における1996年8月の残差流構造 (本文茸英文) 吉田昭治藤原正幸・藤原建紀・大橋行三自由水面をもつような飽和一不飽和浸透流の相似則について,筆者が1966年に不飽和流線網の幾何学的相似性に着目し診断モデルを用いて紀伊水道における1996年8月の残差流て,原型と模型において流れが相似になるには,幾何学的に相の実態を明らかにした。計算結果は,紀伊水道内の2測線で得似な対応点において比透水係数K7(P)(Pは負圧水頭)が両者られたADCPのデータによりその再現性を検証した.表層でで互いに等しいことが必要であることを理論的に提示した. は大阪湾より南下してきた流れが北緯34度付近に存在する反本研究では,この相似に必要な条件はK.(P)=Kr'(λp)(λ 時計回りの渦により西に曲げられ四国沿いを南下し,阿南市沖は2系の幾何学的縮尺率,Kr'は λ倍の系の比透水係数)によで今度は流向を東に変え最終的に紀伊半島に沿って太平洋に流って満たされることを理論的に示し,かつこれを有限要素法に出する。底層は逆に大阪湾に流入する流れとなっている.運動よる数値実験によって確かめた。方程式の各項のバランスを計算すると,海峡部付近では潮汐応力と圧力勾配力が釣り合っているが,ほとんどの海域でコリオキーワード飽和一不飽和浸透流,流線網,相似則,不飽和透水係数,比透水係数,有限要素法,数値実験リカと圧力勾配力が釣り合う地衡流的な流れとなっている.

(農土論集194,pp.81～86) キーワード残差流,診断モデル,紀伊水道,地衡流,密度流,潮汐応力 (農土論集194,pp.87～96)