Proceedings of the 22nd IAHR-APD Congress 2020, Sapporo, JapanANALYSIS OF FLOOD AND RIVER BED VARIATION IN THE KAMANASHI RIVER
WITH LARGE AMOUNT OF SEDIMENT DEPOSITIONSHIRO OKAYAMA
Civil, Human and Environmental Engineering, Chuo University, Tokyo, Japan, a15.4b5c@g.chuo-u.ac.jp
YUKO NAITO
Kofu River and Road Office, Kanto Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism,
Yamanashi, Japan, naitou-y8311@mlit.go.jp
SHOJI FUKUOKA
Research and Development Initiative, Chuo University, Tokyo, Japan, sfuku@tamacc.chuo-u.ac.jp
GOTOH TAKAHISA
Research and Development Initiative, Chuo University, Tokyo, Japan, goto510@tamacc.chuo-u.ac.jp

ABSTRACTThe Kamanashi River is a steep river with gravel grains, cobbles and boulders. In 1982, the record breaking
largest flood occurred and the large amount of sediments yielding in the upstream mountainous area flowed intoand deposited in the river channels. The depositions mainly occurred in the lower reaches where the bed slope
was milder than the upper reaches. In addition, the grain size distributions became coarser in the upper reaches
and finer in the lower reaches due to sorting during the flood. In this study, we developed and applied flood
flow and bed variation analysis method considering the non-equilibrium sediment motions of boulders andgravel grains with large amount of suspended sediments for the 1982 flood. The upstream boundary conditionof the bed variation analysis was given by estimating the large amount of sediment discharge from the upstream
mountainous area. The calculation results clarified the process of the particle distributions fining in the lower
reach and the process of the one becoming coarser in the upper reach. And the calculation results demonstrated
the tendency of the deposition shown in the observed data in the lower reach after the flood.
Keywords: non-equilibrium flow and sediment, upper sediment boundary condition, a large amount of sediments yields,
flood flow, bed variation

1.

INTRODUCTION

The Kamanashi River is a steep river with gravel grains, cobbles and boulders. The well developed doublerow bars are formed as shown in Figure 1(a). In August 1982, the record breaking largest flood occurred and alarge amount of sediment yields occurred in the upstream mountainous area. The large amount of sedimentyields brought large-scale sediment depositions and channel migrations of the double-row bars as shown in
Figure 1(b). In addition, the grain size distributions after the flood became coarser in the upper reaches and finerin the lower reaches compared to those before the flood due to sorting (Ikeda et.al., 1986 and Parker, 1991).
Uwasegi Headworks

Ipponsugi Headworks

13km

14km

15km

16km

17km

18km

：Vegitation

Figure 1(a). Aerial photograph before the flood
Ipponsugi Headworks
Uwasegi Headworks

13km： Vegitation

14km

15km

16km

17km

18km

Figure 1(b). Aerial photograph after the flood
1Parker proposed the bed variation analysis method considering selective sorting and abrasion. The bed load
discharge was calculated by using the equilibrium bed load transport equation in his study. He applied andpredicted the long term changes in riverbed gradients and the downstream sediments fining under conditions ofnear the bunkfull discharge. However, it is necessary to consider the non-equilibrium sediment motions in orderto calculate the large amount of sediment depositions due to active motions of gravel grains in the Kamanashi
River. The objective of the study is to develop the flood flow and bed variation analysis method considering thenon-equilibrium sediment motions in the gravel bed rivers containing large amount of suspended sedimenttransports. In addition, we investigate the mechanism of large-scale sediment depositions and sorting of bed
materials due to 1982 flood of the Kamanashi River by applying the developed method of bed variation analysis.
2.

LONGITUDINAL SEDIMENTATION AND SORTING CAUSED BY THE 1982 FLOOD

Figure 2 shows longitudinal distributions of the flood marks and the measured mean bed elevations before
and after the flood. Flood marks rose to around the designed water levels. In the downstream from 10km point,
the water surface profiles became mild due to the backwater from the Unose contraction reaches and theconfluence of the Fuefuki River.
Figure 3 indicates the measured longitudinal distributions of sediment depositions after the flood. The
1982 flood caused the large amount of sediment yields in the upstream mountainous area and most of thosesediments flowed into the river channel. The amount of sediment depositions in the objective reaches wereapproximately 2 million m3 as shown in Figure 3. And the large-scale sediment depositions tended to occur inthe lower reaches (14km to 5km) where the bed slope was milder than the upper reaches.
Figure 4 shows the grain size distributions of bed materials in the objective reaches before and after theflood. The shape of grain size distributions before the flood was almost same shape for longitudinal directions,and size of D60 was about 20mm. However, the grain size distributions after the flood became coarser in theupper reaches (24km ~ 20km) and became finer in the lower reaches (14km to 5km). The mean size of D60 inupper reaches became 100mm and that in the lower reaches became 3mm. These facts indicated that the coarse
sediments deposited in the upper reaches and the fine sediments were transported to the lower reaches during
the large flood.
350

330
320
310

Elevation(T.P.m)

Sio R.

計画高水位
Designed water level
左岸痕跡水位
Flood mark (left)
右岸痕跡水位
Flood mark (right)
Meanriverbed
elevation (after the flood)
実測(洪水後)平均河床高Meanriverbed
elevation (before the flood)
実測(洪水前)平均河床高340

Midai R.

300
290

Shikamura Weir.

280

TakaiwaWeir.

270

Kamiseki Headworks.

Fuefuki R.

260

the Unose contraction reaches

250

Ipponsugi Headworks.

240

1/180

1/580

1/110

230
2

3

4

5

6

7

8

9

10

11 12 13 14 15 16Longitudinal distance (km)

17

18

19

20

21

22

23

24

Volume of sedimentdepoisition(m³)

Figure 2. Longitudinal distributions of the flood marks and measured mean bed elevations before and after the flood＊：missing observarion

3.E+05
3.E+05
2.E+05
2.E+05
1.E+055.E+040.E+00-5.E+04-1.E+05

Fuefuki R.

Midai R.

Sio R.

＊＊＊

Deposit about 2 million m³

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Longitudinal distance(km)
1/180

1/580
1/110
Bed slopeFigure 3. Measured longitudinal distributions of sediment depositions after the flood
2

Particle size distributions of sediment supply in sediment generation reachParticle size distributions in bed variation analysis reach

Observed particle size
distributions before the flood

0.1

1

25km
13km

23km
11km

10
100
Sediment diameter (mm)
21km
7km

19km
5km

17km
系列1

1000

100
90
80
70
60
50
40
30
20
10
0

Volume percentage finer than (%)

Volume percentage finer than (%)

100
90
80
70
60
50
40
30
20
10
0

0.1

1

10
100
Sediment diameter(mm)

1000

15km

Figure 4(a) the grain size distributions around bed
surface material before the flood3.

Observed particle size
distributions after the flood

Figure 4(b) the grain size distributions around bed
surface material after the flood

ANALYSIS METHOD AND CONDITIONS

3.1 Analysis method
In this study, the quasi-three-dimensional flow analysis method (Q3D-FEBS method, Takemura &Fukuoka, 2019) was applied in order to accurately calculate flood flows and bed variations in the Kamanashi
River with the double-row bars. The Q3D-FEBS method was able to calculate the three-dimensional velocity
distributions and pressure distributions in the framework of the depth integrated model. The velocity
distributions in the vertical direction were determined by the equations of motion on a water surface (𝜂 = 0) anda bottom surface (𝜂 = 1) shown in Eq.(3) and Eq.(4) in addition to the depth-integrated continuity equations andthe momentum equations shown in Eq. (1) and Eq. (2). The elevation of bottom surface was defined as slightly
higher than the bed surface. (𝑧 = 𝛿𝑧 + 𝑧 , 𝛿𝑧 = 𝑐 ℎ, 𝑐 = 0.03)
𝜕ℎ 𝜕𝑈 ℎ
+
=0
𝜕𝑡
𝜕𝑥
𝜕ℎ𝑢 𝑢
𝜕𝑈 ℎ 𝜕𝑈 𝑈 ℎ
𝜕𝑧
1 𝜕ℎ𝑝
𝑝 𝜕𝑧
𝜕
𝜕𝑈 𝜕𝑈
𝜏̂
+
= −𝑔ℎ
−
−
−
+
𝜈𝑡 ℎ
+
−𝑆
𝜕𝑡
𝜕𝑥
𝜕𝑥
𝜌 𝜕𝑥
𝜌 𝜕𝑥
𝜕𝑥
𝜕𝑥
𝜕𝑥
𝜕𝑥
𝜌
𝜕𝑢
𝜕𝑢
𝜕𝑧
1 𝜕𝑝 𝜕𝑧
𝜈 𝜕 𝑢
+𝑢
= −𝑔
+
+
𝜕𝑡
𝜕𝑥
𝜕𝑥
𝜌 𝜕𝑧 𝜕𝑥
𝜌 𝜕𝑧
𝜕𝑢
𝜕𝑢
𝜕𝑧
1 𝜕𝑝
𝜕𝑢
1 𝜕𝑝 𝜕𝑧𝜕𝜕𝑢𝑆 𝜏̂ − 𝜏̂
+𝑢
= −𝑔
−
+
+
𝜈
+
+
𝜕𝑡
𝜕𝑥
𝜕𝑥
𝜌 𝜕𝑥 𝜌 𝜕𝑧 𝜕𝑥
𝜕𝑥
𝜕𝑥
𝜕𝑥
𝜌 𝛿𝑧

𝑢 (𝜂) = ∆𝑢𝑖 (12𝜂3 − 12𝜂2 + 1) + 𝛿𝑢𝑖 (−4𝜂3 + 3𝜂2 ) + 𝑈𝑖

(1)
(2)
(3)
(4)
(5)

where, 𝑖 = 1, 2 (𝑥 = 𝑥, 𝑥 = 𝑦), 𝑢 (𝜂): velocity in 𝑖 direction at any height, 𝑈 : depth-average velocity in 𝑖
direction, 𝑢 : water surface velocity in 𝑖 direction, 𝑢 : bottom surface velocity in 𝑖 direction, ∆𝑢 = 𝑢 − 𝑈 ,𝛿𝑢 = 𝑢 − 𝑢 , 𝑧 : water level, ℎ: water depth, 𝜌: density of water, 𝑢 = 𝑢 - 𝑈 , 𝑔: acceleration of gravity, 𝑝 :non-hydrostatic pressure, 𝜈 :kinetic eddy viscosity coefficient, 𝜏̂ : shear stress acting on the height of bottom
surface velocity in 𝑖 direction, 𝑆 = 1 + (𝜕𝑧 ⁄𝜕𝑥 ) , 𝜏̂ : shear stress acting on the bed surface in 𝑖 direction.
Overbar“–“ represents a depth-averaged value.
The consideration of non-equilibrium sediment motions with a wide range of grain sizes from coarse tofine sediments was important for calculating large-scale sediment depositions and sorting. Therefore, wedeveloped bed variation analysis method for stony and gravel bed rivers (Osada et.al., 2013) consideringsuspended sediment transports. The temporal changes in the volume of bed load were obtained from continuity
equations of bed load in Eq. (6). The sediment discharge per unit was calculated by the volume of bed load andsediment particle velocity in Eq. (7), and the particle velocity was calculated from the saltation analysis (Osadaet.al., 2013) using equations of motion of a sand particle in Eq. (8). The temporal changes in the height of eachparticle size was calculated by pick-up rate and deposit rate in Eq. (9). The deposit rate was calculated by thevolume of bed load and the average moving period in Eq. (10). The average moving period 𝑇 was estimatedby the saltation analysis of each particles. The pick-up rate was obtained from Eq. (11) by calculating the time𝑇required for pick up from river bed (Osada et.al., 2013). The equation of pick-up rate in Eq. (11) took into
account the unevenness distributions of the riverbed elevations composed of each size of particles. Thereby, thismethod was able to calculate the shielding effects of coarse sediments on fine sediments (Osada et.al., 2013).
3

The transport of suspended sediments was calculated by horizontal 2D advection-diffusion equations in
Eq. (12). The suspended sediment entrainments 𝑉 from the bed load motion was calculated by the particle
velocity in the vertical direction in Eq. (13). The particle velocity in vertical direction was estimated by theequation of motion of the particle considering the effects of velocity fluctuations by turbulences in Eq. (14).
The depositions were calculated from the falling velocity and the suspended sediment concentration near the
bed.
𝜕𝑞
𝜕𝑉
+
𝜕𝑡
𝜕𝑥

= −𝑉
𝑞

𝐴 (𝜌 + 𝜌𝐶 )𝑑

+𝑉
=𝑢

−𝑉

(7)

𝑉

𝜕𝑢
1
= 𝜌𝐶 𝐴 𝑑 𝑢 − 𝑢
𝒖 −𝒖
𝜕𝑡
2
𝜕𝑧
𝐴
= − (𝑉 − 𝑉 )
𝜕𝑡
𝐴
1
𝑉 =
𝑉
𝑡
𝑉

,𝜀

=𝜀

𝜕𝐶 ℎ 𝜕 𝐶𝑠𝑘 𝑈ℎ 𝜕 𝐶𝑠𝑘 𝑉ℎ
𝜕
𝜕𝐶
+
+
=
𝜈ℎ
𝜕𝑡
𝜕𝑥
𝜕𝑦
𝜕𝑥
𝜕𝑥
𝑉
𝐴 (𝜌 + 𝐶 )𝜌𝑑
=1
𝐴 𝑑 𝐶 𝜌 𝑤 +𝑤 −𝑤
2

(6)

+𝑉

(8)

− (𝜌 − 𝜌)𝐴 𝑑 𝑔

(9)
(10)

= 0.016
+

(11)

𝜕
𝜕𝐶
𝜈ℎ
𝜕𝑦
𝜕𝑦

+𝑉

(12)

−𝑉

(13)

=𝐶 𝑤

𝑑𝑤
= 𝐹 + 𝐹 − 𝐴 (𝜌 − 𝜌)𝑔𝑑
𝑑𝑡

𝑢 +𝑢 −𝑢+ 𝑣 +𝑣 −𝑣(14)+ 𝑤 +𝑤 −𝑤−𝐴 (𝜌 − 𝜌)𝑔 𝑑

where, 𝑉 ：volume of bed load, 𝑞 ：sediment discharge per unit width in 𝑖 direction, 𝑉 ：deposition rate,
𝑉 ：pick-up rate, 𝑢 ：particle velocity in 𝑖 direction, 𝜌 : gravel particle density, k : particle numbers, dk :particle diameter, 𝐴 and 𝐴 : a two-dimensional and three-dimensional shape factor (=𝜋⁄4, 𝜋⁄6), respectively,
𝑤 : vertical particle velocities, 𝐹 : the fluid forces generated by turbulence, 𝐹 : fluid forces by mean flow
velocities near the bottom.
3.2 Calculation conditions
Figure 5 shows the objective area and the locations of boundary conditions.The tributaries which werethe Shio River, the Midai Rver, the Fuefuki River and the Ashi River were taken into account in the calculations.
The upstream boundary condition of flood flow in each rivers was given by the discharge hydrographs obtained
from the runoff analysis. The downstream boundary condition was given by observed water level hydrographat Shimizubata observation station (2.7k) shown in Figure 6.
A large amount of inflow sediment discharge graph from the upstream mountainous basin during theflood should be taken into account as the upstream boundary condition of bed variation analysis of the Kamanasi
River and the tributaries. The determination method of the inflow sediment discharge graph of these rivers was
explained below. Figure 7 shows schematic diagram determining the upstream boundary conditions for bed
variation analysis. It was assumed that the inflow sediment discharge of each particle sizes from the upper
reaches was produced by sediment entrainments due to flood flows in the sediment generation reach (see Figure
Kamanashi River

Shimizubata(2.7k)

Funayamabashi(23.8k)
Horikiri
Midai River

Sio River
Kongoji

Ashi River.

Asaharabashi(10.8k)
Tourinkyo(4.5k)

Fuefuki River

Google Earth

Figure 5. The analysis reach
4

3000

250
248
246
244

2000

242
1500

240
238

1000

236

Water level(T.p.m)

Discharge(m3/s)

2500

234

500

232
0

230
0

5

10
Flood duration time(hour)

1520

Figure 6. discharge hydrographs and observed water level of Shimizubata (2.7k)

23k

25k

24k

flow

Funayamabashi

Bed variation analysis reachTransition reach

Sediment generation reachFigure 7. Calculation method of upstream boundary condition for the bed variation analysis

35
30

1,200,000

7

1,000,000

6

800,000

25

600,000

20
15

400,000

10

200,000

5
0

0
0

5

10
15
Flood duration time(hour)

20

Figure 8(a). Sediment graph of the Kamanashi River

Accumulated total sediment volume140,000

Midai River

120,000

5

100,000

4

80,0003

60,0002

40,0001

20,0000

Sediment volume(m³)

Kamanashi River

40

Suspended load discharge graph

Sediment discharge(m³/s)

Sediment discharge(m³/s)

45

Bed load discharge graph

Sediment volume(m³)

Total sediment discharge graph

0
0

5

10
15
Flood duration time(hour)

20

Figure (8b). Sediment graph of the Midai River7) so as to agree with the observed bed variation and bed material distributions in the downstream reach. The
bed gradients and channel widths in these reaches were given by the average channel width and bed slope around25km point. The grain size distribution in the sediment generation reach was set so as to contain the finesediment observed in the lower reach and the coarse sediment observed in the upper reach after the flood asshown in Figure 4(b).
The initial grain size distributions in the bed variation analysis are given based on the grain size
distribution before the flood shown in Figure 4 (a). The transition reach was set between the sediment generation
reach and the bed variation analysis reach. The sediment discharge graphs containing bed load and suspended
load were formed in the transition reach and introduced as the upstream boundary condition of the bed variation
analysis in the downstream.
Figures 8(a) and 8(b) show the sediment graphs of the Kamanashi River and the Midai River given as theboundary conditions of upstream end. The shape of the sediment graph was assumed to be similar to that of thedischarge hydrograph. About 1,000,000 m3 of sediment flowed into from the Kamanashi River, and about
120,000 m3 from the Midai River.
4.

ANALYSIS RESULTS

Figure 9 shows the distribution of flood marks, calculated water surface profiles, the observed andcalculated mean bed elevations before and after the flood. The calculated water surface profiles at 9hours(peaktime) explained the observed water surface profile that was raised due to the Unose contraction reach and theconfluence of the Fuefuki River, although it was higher than the flood marks in the reach between 24 km and
5

350
345

Sio R.

Midai R.

340

Elevation(T.P.m)

335

Shikamura Weir.

Takaiwa Weir.

330
325
320
315
310
305
300
295
290
18

19

20

21
Longitudinal distance(km)

22

23

24

6

7

8

9
Longitudinal distance(km)

10

11

12

270
265

Elevation(T.P.m)

260
255
250
245
240
235
230

the designed water level
Analyzed mean bed elevation(5hour)
Analyzed mean bed elevation(9hour)
Analyzed mean bed elevation(13hour)
Flood mark(right side)
Observed mean bed elevation(after flood)

Analyzed mean water level(5hour)
Analyzed mean water level(9hour)
Analyzed mean water level(13hour)
Flood mark(left side)
Observed mean bed elevation(before flood)

Figure 9. Longitudinal distribution of analyzed mean water level and analyzed mean bed level

23 km. In the reach between 24 km and 23 km, the calculated mean bed elevations became higher than themeasured one, because the inflow sediment discharge from the upper reaches tend to deposit in this reach. Figure
10 indicates the longitudinal distribution of the amount of bed load and Figure 11 indicates the longitudinal
distribution of the amount of suspended sediment. The amount of bed load of the grain size 100mm to 500mm
gradually decreased from 23km to 13km at 9 hours (peak time). And the bed load with grain size of 8mm to30mm shows a sharp decreasing in the longitudinal direction at peak time in the reaches between 23km to 21km
and 13km to 12km. Therefore, the sediment depositions occurred in these reaches. From Figure 10 and Figure
11, the sediments with grain size of 0.5mm to 1.5mm were almost transported in states of suspensions. The
suspended sediments decreased significantly in the reaches from 10km to 6km where the water surface gradients
became mild after 9 hours (peak time).
Regarding the calculation results in the lower reaches, Figures 12(a), (b) and 12(c) show the depthaveraged suspended sediment concentration, existence ratio of particle size of 0.5mm to 1.5mm on bed surface,and contour of bed variation before and after the flood, respectively. At 5 hours (flood rising period), thesuspended sediments from the upstream boundaries did not almost reach to the downstream of 10km point
shown in Figure 11. Therefore, the suspended sediment concentration in this reach was low at this time shownin Figure 12(a). However, at 9 hours (peak time), the suspended sediments reached from upstream boundaries
to the lower reach as shown in Figure 11. Thus the suspended load concentration increased after 9hours asshown in Figure 12(a). The amount of suspended sediment concentration decreased longitudinally in the reachfrom 10 km to 6 km due to mild water surface profiles and sediment depositions occurred as shown in Figure12(c). Thus, the calculation results demonstrated that the bed materials on the bed surface became finer due tothe deposition of suspended sediments in this reach. On the other hand, the calculated mean bed elevations werelower than the observed one. It is necessary to determine the inflow sediment discharge at the upstream end
properly by using the developed bed variation analysis method.
6

1.2
Sio R.

Sediment discharge(m3/s)

Midai R.

1
Uwasegi Headworks.

Ipponsugi Headworks.

TakaiwaWeir.

Shikamura Weir.

18

20

0.8
0.6
0.4
0.2
0
6

7

8

9

10

11

12

13

14

15

16

17

19

21

22

23

24

23

24

Longitudinal distance(km)0.5mm～1.5mm_5h
0.5mm～1.5mm_9h

8mm～30㎜_5h
8mm～30㎜_9h

100mm～500㎜_5h
100mm～500㎜_9h

Figure 10. longitudinal distribution of amount of bed load
Sediment discharge(m3/s)

30

Sio R.

Midai R.

25
Ipponsugi Headworks.

Uwasegi Headworks.

20

Shikamura Weir.

TakaiwaWeir.

15
10
5
0
6

7

8

9

10

11

12

0.5mm～1.5mm_5h

13 14 15
16 17Longitudinal distance(km)0.5mm～1.5mm_9h

18

19

20

21

22

0.5mm～1.5mm_13h

Figure 11. longitudinal distribution of amount of suspended load

flow

10k

9k

6k
(5hour)

10k

9k

9k

7k

7k

flow

6k

6k

(9hour)(13hour)

10k

10k

10k

8k

8k

8k

7k

7k

7k

6k

6k

6k

(5hour)(9hour)

9k

9k

9k

8k

8k

8k

6k
(13hour)

7k

7k

7k

10k

10k

flow 10k

9k

9k

9k

8k

8k

8k

7k

10k

6k

6k
(5hour)(9hour)(13hour)

Depth-averaged suspended sedimentconcentration (%)

Existence ratio on bed surface (%)

Riverbed variation (m)Figure 12(a).
Depth-averaged suspended sedimentconcentration contour

Figure 12(b).
Existence ratio on bed
surface (0. 5mm～1.5mm)

Figure 12(c).
Contour of bed variation
before and after the flood

In upper reaches, Figure 13(a) shows existence ratio of particle sizes of 0.5mm to 1.5mm on bed surface
at 5 hours. And Figures 13(b) to 13(d) show existence ratio of particle sizes of 0.5mm to 1.5mm, 8mm to 30mm,
and 100mm to 500mm during the flood receding period (13 hours), respectively. The initial existence ratio on
bed surface was that the particle size of 0.5mm to 1.5mm was 20%, 8mm to 30mm was 40% and 100mm to500mm was 40%. At 5 hours in the flood rising period, the fine sediments deposited largely and the riverbed
surface became finer. However, around 9 hours, the relatively coarse sediments whose sizes were 8mm to 30mm
7

Existence ratio on bed
surface materials (%)

Sio R.

Sio R.

Sio R.

24k

24k

24k
23k

23k

Sio R.
24k

23k

22k

22k
Kamanashi R.
21k

Kamanashi R.
21k

23k

22k

22k

Kamanashi R.

Kamanashi R.

21k

Figure 13. Existence ratio on bed surface materials (%)
(b).
(c).
(a).
100mm～500mm
8.0mm～ 30mm
0.5mm～1.5mm(13hour)(13hour)(5hour)21k(d).
0.5mm～1.5mm(13hour)flowed into this reach as shown in Figure 10, and the existence ratio of 8mm-30mm sizes increased to 50-60%
as shown in Figure 13(c). The calculation results indicated that bed materials became coarser due to inflow
sediment discharge. But these calculation results were smaller than the measured particle size distributions after
the flood shown in Figure 2. It is necessary to examine effects of volume, shapes and phase shift of sedimentgraph of each particle sizes in relation to discharge hydrograph at the upper boundary on changes in riverbed
and bed materials in the downstream reaches.
5.

CONCLUSION

In this study, we developed a quasi-three-dimensional flood flow and bed variation analysis considering
the non-equilibrium motion of boulders and gravel grains with a large amount of fine sediment motions. The
developed method was applied to the 1982 flood in the Kamanashi River where a large amount of depositions
and sorting of transported sediments occurred. The calculation results demonstrated that most of fine sediments
were transported in states of suspensions to the lower reaches and it deposited in the reach where the water
surface profiles became mild due to the Unose contraction reach and the confluence of the Fuefuki River. Thus,
bed materials in the lower reaches became finer than sands shown in the observed data. In upper reaches, thecalculated bed materials tended to become coarse around the time of the peak discharge.
However, the amount of sediment depositions in the calculations were much smaller than the observed
one. And the analysis method was not able to calculate depositions of a particle size exceeding 100 mm observedin the upper reaches after the flood. Therefore, it was demonstrated that the determination method of the
upstream boundary should consider the volume, shapes and phase shift of sediment graph of each particle sizes
in relation to discharge hydrograph at the boundary.
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