ODMP Workshop Report Slides Hydrology component

8/8/2019 ODMP Workshop Report Slides Hydrology component

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Okavango Delta Management Plan Integrated Hydrological Model

FlowFlow ProcessesProcesses


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MIKE SHEMIKE SHE

Physically based

Complete land phase of hydrologicalcycle

Evapotranspiration from surfacewater, vegetation and soil

Surface water flows through riversand swamps

Sub-surface flows in root zone andground water

Integration of atmospheric, surfaceand ground waters

The MIKE SHE Integrated Hydrologic Model provides a water balanceand flow model for the delta, capable of analysing the short term andlong term impacts on the delta of upstream inflows, climate changes and

water abstractions.


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ET and energy balance of the SVAT modelET and energy balance of the SVAT model

R = solar radiation

S = temporary stored energy

H= sensible heat fluxE = energy lost by ET

Loss/gain of energy by horizontal air movement

G= heat conduction to the soil

ET loss from water surfacesSoil ET loss

Veg. Tran-spiration loss

Groundwater

Flooded area

Reflected solar radiation


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Surface Vegetation Atmosphere Model (SVAT)Surface Vegetation Atmosphere Model (SVAT)Vegetation parameters distributed by vegetation map - aggregated into 6 main veg. types


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Surface Vegetation Atmosphere Model (SVAT)Surface Vegetation Atmosphere Model (SVAT)Satellite data (MODIS) of vegetation density used in SVAT simulation of distributed actual ET rates

10 days composites gap filled in cloud covered areas


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MIKE SHE SVATMIKE SHE SVAT -- outputsoutputs

Key output in hydrologicalKey output in hydrological modelingmodeling ::-- EvapotranspirationEvapotranspiration losseslosses

-- EnergiEnergi fluxesfluxes-- Temperature of surface, vegetationTemperature of surface, vegetation-- ResistancesResistances and many more and many more

ET rates simulated by MIKE SHE SVAT in permanently flooded

and temporarily flooded areas


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MIKE11MIKE11 -- Okavango DeltaOkavango Delta

Main characteristics affecting

conceptual and numerical model

Flow separation and bifurcations

rather than confluences

Extensive spills with numerous cross

flowing floodplains

Complex flow pattern - impossible to

separate 1-D and 2-D flowInter basin runoff of lesser importance

compared to river inflows

Slowly wave propagation (3 months from

upstream to downstream) and yet highly

dynamic flooding extent (monthly,

seasonally, yearly)

UPSTREAM FLOW SPLITS ARE

ESSENTIAL TO REPRESENTACCURATELY IN ORDER TO SIMULATE

DOWNSTREAM FLOW AND SPILLS

ThaogeJao/Boro

Nqoga/Kwai

1 level : downstream panhandle2 level : proximal fan3 level : distal fan


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MIKE11MIKE11 -- MIKE SHE flood plain couplingMIKE SHE flood plain coupling

MIKE11 (1MIKE11 (1 --D)D) MIKE SHE OL (2MIKE SHE OL (2 --D)D)

dxdx dxdx

ET lossET loss

Infiltration lossInfiltration loss

MIKE11MIKE11 XsecXsec geometrygeometry

MIKE SHE topographical modelMIKE SHE topographical model

MIKE SHE flood code cellMIKE SHE flood code cell


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Simulation of flood extent and flood durationSimulation of flood extent and flood durationDownstream panhandle and proximal fan during flood season

Flow in flooded areas handled by 2-D MIKE SHE overland flow model

Flow in rivers/channels handled by 1-D MIKE11 hydrodynamic modelThe two models are dynamically coupled to account for floodplain spills and return flows


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Groundwater dynamics of delta islandsGroundwater dynamics of delta islands

High flood level

Low flood level


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Unsaturated zoneUnsaturated zone -- model approachmodel approach1) Unsaturated zone includes 4 characteristic

soil types - all relatively uniform. Hydraulic

properties derived from soil sample data

applying pedo-transfer functions (Rosetta)

2) Since the soils according to grain analysis

are sandy capillary forces can be ignored

(gravitational flow approximation applied).


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Unsaturated zone and groundwater Unsaturated zone and groundwater Infiltration rates are significant on the

predominantly sandy soils in the early stages

of the flood season. Infiltration on newly

flooded areas raises the groundwater table to

the flood water levels.

Fresh water lenses replenished by flooding

embedded in older salt ground water.

Very limited topographical relief - low

groundwater flow rates directed towards

local depressions

Hypothesis of significant regional

groundwater flow across downstream fault line

can not be supported by data or model test.Insignificant with respect to delta water

balance

(Maun GW development project)


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Saturated zoneSaturated zone -- model approachmodel approachGroundwater component is included to

account for the local effects of

groundwater on the water balance

(recharge/discharge due to dynamic

flooding, ET losses from groundwater)

Consequently, only the surficial ground

water aquifer represented in the model.

No flow boundary assumed along model

boundary


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Upstream InflowsUpstream Inflows

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

1 9 3 3

/ 3 4

1 9 3 8

/ 3 9

1 9 4 3

/ 4 4

1 9 4 8

/ 4 9

1 9 5 3

/ 5 4

1 9 5 8

/ 5 9

1 9 6 3

/ 6 4

1 9 6 8

/ 6 9

1 9 7 3

/ 7 4

1 9 7 8

/ 7 9

1 9 8 3

/ 8 4

1 9 8 8

/ 8 9

1 9 9 3

/ 9 4

1 9 9 8

/ 9 9

D i s c

h a r g e ( M

m 3 / a )

Mohembo

Mukwe

5 year moving average5 year moving average


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Upstream InflowsUpstream Inflows

0

2,000

4,000

6,000

8,000

10,000

12,000

1992/93 1993/94 1994/95 1995/96 1996/97 1997/98 1998/99 1999/00 2000/01 2001/02

D i s c

h a r g e

( M m

3 / a )

Mohembo

Mukwe

critical period

normal period


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Delta ZonesDelta Zones

Based on satellite analysis(J McCarthy, Stockholm University)

MODEL AREA (km2) 28,782Zone 1 - 0.1>FF>0 19,322 rarely floodedZone 2 - 0.5>FF>0.1 3,534 occasionally floodedZone 3 - 0.9>FF>0.5 2,328 seasonally floodedZone 4 - 1>FF>0.9 2,152 permanently floodedZone 5 - Panhandle 1,446 Panhandle


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Water BalanceWater BalanceWATER BALANCE (mm/annum) Baseline

AngolaDams

U/SIrrigation

DeltaAbstraction

ClimateChange

Precipitation -393 -393 -393 -393 -360Evapotranspiration 691 694 667 691 590

Inflow -217 -220 -190 -217 -135

Outflow 6 6 6 6 6

Overland Storage Change -37 -38 -40 -37 -45

Subsurface Storage Change -48 -48 -49 -48 -54

TOTAL 2 2 2 2 1


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Baseline Overland FlowBaseline Overland FlowDry Period

(1992 to 1997)Overland Depth

of Flow (m)


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Minimum Depth of Overland FlowMinimum Depth of Overland FlowDry Period (1992

to 1997)Minimum Depth

of Flow (m)


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Time Series of Overland FlowTime Series of Overland Flow


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Flooded AreaFlooded AreaIMPACTS Baseline AngolaDams

U/SIrrigation

DeltaAbstraction

ClimateChange

Minimum Flooded Area (km2) 1,513 -33 -661 -4 -736

zone 1 (Rarely Flooded) 15 0 -14 -1 -15

zone 2 (Occasionally Flooded) 19 0 -5 0 -6

zone 3 (Seasonally Flooded) 227 -13 -118 -3 -132

zone 4 (Permanently Flooded) 934 -18 -303 0 -343

zone 5 (Panhandle) 318 -2 -221 0 -240

Maximum Flooded Area (km2) 12,077 93 -75 -7 -716

zone 1 (Rarely Flooded) 4,426 78 -47 -14 -450zone 2 (Occasionally Flooded) 2,573 9 -21 4 -139

zone 3 (Seasonally Flooded) 2,045 7 -7 1 -73

zone 4 (Permanently Flooded) 2,076 -1 1 2 -43

zone 5 (Panhandle) 957 0 -1 0 -11

k l l I d H d l i l M d l


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Soil MoistureSoil MoistureDry Period (1992 to

1997)

Soil Moisture

Deficit (mm)

Ok D l M Pl I t t d H d l i l M d l


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Ground Water Ground Water Dry Period

Maximum Depth to

Ground Water (m)

Ok D lt M t Pl Integrated H drological Model


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Dams in AngolaDams in Angola

0

50

100

150

200

250

300

350

400

450

500

Oct 92 Apr 93 Oct 93 Apr 94 Oct 94 Apr 95 Oct 95 Apr 96 Oct 96 Apr 97 Oct 97

D i s c

h a r g e

( m 3 / s )

Recorded

WERRD-08



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Inflow with IrrigationInflow with Irrigation

0

100

200

300

400

500

Oct 92 Apr 93 Oct 93 Apr 94 Oct 94 Apr 95 Oct 95 Apr 96 Oct 96 Apr 97 Oct 97

D i s c

h a r g e ( m

3 / s )

Recorded

Irrigation



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Impact on Overland DepthImpact on Overland DepthDry Period (1992 to

1997)

Difference in

Depth of Flow (m)



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Inflow from Upstream BasinInflow from Upstream Basin

0

200

400

600

800

1,000

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

D i s c

h a r g e ( m

3 / s )

Observed

Climate Change



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Precipitation and TemperaturePrecipitation and Temperature

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Oct 92 Oct 93 Oct 94 Oct 95 Oct 96 Oct 97 Oct 98 Oct 99 Oct 00 Oct 01 Oct 02

T e m p e r a

t u r e

( d e g C

)

Average Daily Temperature Change: 19.9 to 22.1degC

Precipitation Change: 393 to 360mm/a



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Impact on Overland FlowImpact on Overland FlowDry Period (1992

to 1997)

Difference inDepth of Flow (m)



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Okavango Delta Management Plan g y g

Impact onImpact on OverLandOverLand FlowFlow

Documents

ODMP Workshop Report Slides Hydrology component