Final Presentation 7 August 2009

8/3/2019 Final Presentation 7 August 2009

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Della Permata YSEP2008

IKEDA laboratoryCivil Engineering

DepartmentTokyo Institute of

Technology

PRESENTATION- August 7th ,2009


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What is artificial flood

??


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BACKGROUND


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Detachment Algae by BedLoad in Downstream Region

of DAM

There is relation betweenbed load and algaedetachment.

The flush discharge withfine gravel supply is

indispensable to remove

By Dr. YoshihisaAkamatsu

PREVIOUS RESEARCH


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No.0+10

126

128

130

132

134

136

138

140

142

0 10 20 30 40

(m)

(TP

.

40m3/s

20m3/s 2m3/s

8m

Picture of sediment

The amount of sediment was200 m3

Artificial flood with sedimentsupply on February 18, 2009

Location of

sedimentsupply near

Ishigoya DAM

DischargeHydrograph

0

00

00

00

00

00

0 0 0 00 00 00 00 00 00 11

m / s0

m / s0


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OBJECTIVETo evaluate the effectiveness ofthe recent artificial flood withsediment supply (on February 18th,2009) for removing attached algaeand improving the environmentcondition along the river

STUDY FIELDNakatsu River, Kanagawa Prefecture,

Japan


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FOCUS ON MY

STUDYComparing the change of the

amount of attached algae beforeand after flood by comparing

1.FIELD OBSERVATIONresult in real condition of river bedand

2.NUMERICALCALCULATIONresult in ideal

condition of river bed (which there


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AREA OF FIELD OBSERVATION ONFEBRUARY 17-19, 2009

sampling point of attachedalgae before and after

flood at point


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Result of FieldObservationBefo

re

AfterPictures of sedimentsupplied

Water level

reached maximum

value


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RESULT OF FIELDOBSERVATION


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OUTLINE OF NUMERICALCALCULATIONA numerical model to predict the amount

of detached algae was conducted underthe hypothesis that there is enoughsediment with the effective graindiameter size (about 10 mm) to remove

the attached algae.The flowchart of numerical calculation


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Governing Equation of NumericalModelBasic continuity equation of 2D flow

in (x,y) co-orthogonal coordinatesystem

h : depth (m)t : time (s)u, v : velocity (m/s)x, y : distance (m)V : total velocity(m/s)

Depth average flowmodel

In which


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Governing Equation of NumericalModel

0

0.5

1

1.5

2

0 0.01 0.02 0.03 0.04 0.05 0.06

P(10

-4/s)

*

The relation equation between Bed shear stress and survival rate

percentage

The empirical relation between theshear stress ( *) and attrition rateof amount of attached algae perunit time (P) under the condition of10 mm sediment is supplied

The empirical formula fromgraph

* : bed shear stressSg : specific relative weightg : gravity acceleration (m/s2)nm : mannings roughness

coefficientd : diameter of bed material

(m)h : depth (m)P : attrition rate of amount ofattached algae per unit time(/s)tuk : duration time (s)

Cd : dimensionless coefficient


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Method of CalculationThe calculation was conducted for observed

flush discharge in the calculation area

Boundary condition at the upstream

Flow discharge is given by observed values

Velocity is calculated under the assumption of

uniform flow

Boundary condition at the downstream

The observed water depth is calculated underthe assumption of uniform flow

mannings coefficient of roughness (n) is setto be calculated from bed material. (n=0.03)

It is assumed that the filamentous algae is insaturated state cover all river bed before flush


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RESULT OF NUMERICALCALCULATION

Before flood

After flood

1 2 3 4 5


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COMPARISON RESULT BETWEEN FIELDOBSERVATION AND NUMERICAL

CALCULATION

Survival rate percentage from field observation is higher

than those from numerical calculation result. It indicates

that sufficient supply of artificial sediment is required to

remove all of algae for this flood discharge.


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CONCLUSIONThe artificial flood conducted in

Miyagase Dam along Nakatsuriver was not much effective in

algae detachment.This result suggests that theartificial flood with the

sufficient amount of sedimentsupply which contains effectivegrain diameter size is

important to remove the


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Thank You for Your

Kind Attention

Final Presentation 7 August 2009

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