Water level statistics in Delta Areas

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2

Water level statistics in delta areas

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2 - Water level statistics in delta area

Geert de Vries

Water level statistics in Delta Areas

Geert de Vries Geert de Vries

Overview

• Objective of study

• Characteristics of the Volga Delta • Modeling the Volga Delta

• Current state of the model

• Aspects of the model to be researched

Geert de Vries

Objectives of study

• To make a numerical model of the lower Volga Delta (1D as well as 1D/2D) • Use these models for a Value of

Information analysis

Geert de Vries

Characteristics of the Volga Delta

• A widely varying discharge near the head of the Delta (5.000 – 20.000 m3/s)

• A small bottom slope (O (5 * 10^-5))

• Caspian Sea has a rapidly changing water level (max -26.5 in 1995) • Between 500 and 1000

branches

Discharge near head of Delta in 1978

0 5000 10000 15000 20000 25000 125497397 121 145 169 193 217 241 265 289 313 337 361 Discharge (m3/s) Ti m e ( d ay s) Geert de Vries

Modeling the Volga Delta

• Use of a numerical model in Sobek software

package

• Model consists of a network of nodes and branches determined from 1:100.000 maps containing height levels, depths and widths of the channels

• Upper boundary condition: Discharge in Volga and Akhtuba river

• Lower boundary condition: Water level in Caspian Sea

Geert de Vries

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2 - Water level statistics in delta area

Geert de Vries

Current state of model

• Nodes and branches finished

• Cross-sections need refining

• Start calibration and validation

• Implement a 2D overland flow grid to simulate flooding of parts of the delta during high discharge -26 -25 -24 -23 -22 -21 -20 1265176 101 126 151 176 201 226 251 276 301 326 351 measured model

Water level of a simulation compared to measured data for a node a little south of

Astrakhan _{Geert de Vries}

Aspects of the model to be

researched

• Water level probability functions • Q-h Relation

• Value of information analysis

Geert de Vries

Water level probability functions

1 2 3 4 x 104 0 2 4 6 8x 10 -5 _{Uppe r BC Dis tr.} 0 0.5 1 1.5 -28 -27 -26 -25

Lowe r BC Dis tr. Contour plot of joine d p.d.f.

1 2 3 4 x 104 -28 -27 -26 -25 2 4 6 x 10-5 1 2 3 4 x 104 -28 -27 -26 -250 0.5 1 x 10-4

3D-vis ua liz a tion of joine d p.d.f.

Geert de Vries

Water level probability functions

-2 6.2 96₇ -2₅ .9 79 -2₅ .6₆ 13 -2₅ .34₃ 6 -2 5 .0 26 -25.026-2 4.7083 -2 4.3906

Uppe r BC(Dis c ha rge , m3/s )

L o w e r B C (W at er L e v e l C S , m ) E qui wa te r le ve l c urve s 1 2 3 4 x 104 -28 -27 -26 -25 -26.5 -26 -25.5 -25 -24.5

Contour plot of joine d p.d.f.

1 2 3 4 x 104 -28 -27 -26 -25 2 4 6 x 10-5 1 2 3 4 x 104 -28 -27 -26 -25 Geert de Vries

Water level probability functions

-27 -26.5 -26 -25.5 -25 -24.5 -24 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

P .d.f. of water leve l ba s ed on p.d.f.'s of upper and lowe r B.C.'s

Geert de Vries

Q-h Relation

Interesting because of:

- High discharge during small part of the year - Low bottom slope

(O(5*10^-5))

Q-h Graph for head of delta for 1978

0 5000 10000 15000 20000 25000 -25.5 -24.5 -23.5 -22.5 -21.5 -20.5 h values Q -val u e s

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2 - Water level statistics in delta area

Geert de Vries

Value Of Information

• Compare added value of information to effort and time of extra research: How does additionally collected data influence the (accuracy of the) results of the model?

• Define accuracy of model in relation to failure probability