dsd-int 2015 - identification of mixing zones in the eu – a tiered approach - dju bijstra,...

Experiences with mixing zones in the Netherlands

Dju Bijstra (RWS)

Frank Kleissen (Deltares)

Christophe Thiange (Deltares)

Rijkswaterstaat

2 Experiences in with mixing zones in the Netherlands

RWS UNCLASS

Contents

• Context

• Discharge test

• Tiered approach

• developments of the discharge test

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RWS UNCLASS

Why using the discharge test?

• WFD objectives

- Good ecological status (2027)

- Good chemical status (2027)

• Insight in relation (point)sources and waterquality is necessary

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RWS UNCLASS

Mixing zones: why used and restricted?

• where two watercourses join there is a mixing zone

• difference in flow

• difference in concentration

• as long as Cdischarge > Csurface water there is a mixing zone

• as long as Cdischarge > EQS there is an area of exceedance

C > EQS

Mixing zones are inevitable

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RWS UNCLASS

x L

MAC-mixing zone:

(acute effects)

EQS-mixing zone:

(chronic effects)

Because of the ecological significance

of (river)banks concentration at the

bank is calculated and used as a starting

point for the assessment

LengthMAC-mixing zone (Xmac) :

0,25*Width (max 25 m)

LengthEQS-mixing zone (XL):

10*Width (max 1000 m)

Mixing zone

For calculating the dimensions of a mixing zone an application “the

discharge test” has been develloped.

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RWS UNCLASS November 20, 2015

Starting points: discharge test

Fast and easy

Little info needed

EXPERT DETAILED RESEARCH Time consuming

Lots of data needed

sieve

Worst case (low flow) conditions:

Q90 and max. load

Inert behaviour substances

Non problems

Potential problems Complex modelling

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RWS UNCLASS

Experiences with the discharge test in the Netherlands

• The discharge test has been developed in the Netherlands in 2000

• Assessment with discharge test is required for a permit

• Most discharges can the meet the criteria

• In 2011 the EU-guidance on mixing zones was adopted

• In 2011 the NL-discharge test has been adapted to this guidance

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RWS UNCLASS

Tiered Approach (1)

• TIER 0: Are (prioritary) substances present in the discharge in concentrations >EQS? NO Stop

• TIER 1: is the discharge significant? NO Stop

Yes

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RWS UNCLASS

Tier 1: Significancetest

Stop Yes

Is Ccomplete mixing significant?

Attention!:

For discharges at sea and lakes with a width

> 2000 m and harbours the siginifance test can NOT

be applied!

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RWS UNCLASS

watersystem width [m] Allowed (trivial) increase in concentration (% EQS)

(after complete mixing)

fresh waters and tidal rivers*)

Small ≤ 100 1

Middle 100 < width ≤ 400 0,75

large > 400 0,1

Canals

all all 1

Can criteria in

table be met?

Stop Yes

Is Ccomplete mixing significant?

Tier 1: Significancetest

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RWS UNCLASS

Tiered Approach (2)



• TIER 2: determination of mixing-zone whith the discharge-test:

are dimensions of MAC-MZ and/or EQS-MZ

bigger than criteria proposed? NO Stop

Yes

Yes

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RWS UNCLASS

Tiered Approach (2)



• TIER 2: determination of mixing-zone whith the discharge-test:

are dimensions of MAC-MZ and/or EQS-MZ

bigger than criteria proposed? NO Stop

• TIER 3: Complex modelling: Is MZ a problem? NO Stop

• TIER 4: Local (effect)assessment (i.e. bioassays) (optional):

Is MZ a problem? NO Stop

Yes

Yes

Yes

Yes

measures or

or measures

measures Yes If necessary new complex modelling

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RWS UNCLASS

Modeling tools for Tier 2

• Excell discharge test (fresh (streaming) waters) (simple and the amount of input data needed is limited)

• Web-based application (fresh waters; harbours; tidal waters) (more input data are needed)

• http://apps.helpdeskwater.nl/prog/extra/immissietoets/sources/#version=nl-nl

http://apps.helpdeskwater.nl/prog/extra/immissietoets/sources/#version=nl-nl





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RWS UNCLASS

Developments of the discharge test

Discharge test 2000 (spreadsheet)

New tools 2011:

Webbased application and spreadsheet

WFD and guidance on mixing zones

Complexity of tidal waters

Database with Water-

system parameters

User experiences

New tools 2015:

New environment for Webbased application

Database with water quality data

Database with water quality standards

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RWS UNCLASS April 2011

How it works

• Based on a combination of mixing factors:

– Backgroundmixing

– Additional plume/jet mixing:

• Substances not affected by processes other than mixing

• The calculations depend on the type of receiving water

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Rivers/Canals

No density difference: plume calculation using Fisher’s description

With density difference: jet calculations using jet3D (3-dimensional)

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Harbours

Concentration resulting from:

Exchange harbour and main water body and plume/jet

Exchange of water

between harbour and

main waterbody due to:

• Tidal exchange,

• eddies,

• density difference.

In addition optional other

discharge

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RWS UNCLASS

Tracer simulations

20 november 2015

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1

0 5 10 15 20 25 30 35

Tijd (uren)

Co

ncen

trati

e(-

)

Exponentieel (T=0.862d)

Model gebied L008

( )ll

l

VQ

C T

C Q

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RWS UNCLASS

Waterbody properties from database

20 november 2015

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RWS UNCLASS

Questions?

• Thank you for your attention!

Workshop 4 pm in Room Ambition.

Questions ?

dsd-int 2015 - identification of mixing zones in the eu – a tiered approach - dju bijstra,...

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