identification of mixing zones in the EU

1. Experiences with
mixing zones in the
Netherlands
Dju Bijstra (RWS)
Frank Kleissen (Deltares)
Christophe Thiange (Deltares)

2. Rijkswaterstaat
2 Experiences in with mixing zones inRWS UNCLASS
Contents
• Context
• Discharge test
• Tiered approach
• developments of the discharge test

3. Rijkswaterstaat
3 Experiences in with mixing zones inRWS 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

4. Rijkswaterstaat
4 Experiences in with mixing zones inRWS 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

5. Rijkswaterstaat
5 Experiences in with mixing zones inRWS 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.

6. Rijkswaterstaat
6 Experiences in with mixing zones inRWS 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

7. Rijkswaterstaat
7 Experiences in with mixing zones inRWS 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

8. Rijkswaterstaat
8 Experiences in with mixing zones inRWS 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

9. Rijkswaterstaat
9 Experiences in with mixing zones inRWS 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!

10. Rijkswaterstaat
10 Experiences in with mixing zones inRWS 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

11. Rijkswaterstaat
11 Experiences in with mixing zones inRWS UNCLASS
Tiered Approach (2)
• TIER 0: Are (prioritary) substances present in the discharge in
concentrations >EQS? NO  Stop
• TIER 1: is the discharge significant? NO  Stop
• 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

12. Rijkswaterstaat
12 Experiences in with mixing zones inRWS UNCLASS
Tiered Approach (2)
• TIER 0: Are (prioritary) substances present in the discharge in
concentrations >EQS? NO  Stop
• TIER 1: is the discharge significant? NO  Stop
• 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
ormeasures
measures Yes
If necessary new complex modelling

13. Rijkswaterstaat
13 Experiences in with mixing zones inRWS 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/#ver
sion=nl-nl

14. Rijkswaterstaat
14 Experiences in with mixing zones inRWS 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

15. Rijkswaterstaat
15 Experiences in with mixing zones inRWS 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

16. Rijkswaterstaat
16 Experiences in with mixing zones inRWS UNCLASS April 2011
Rivers/Canals
No density difference: plume calculation using Fisher’s description
With density difference: jet calculations using jet3D (3-dimensional)

17. Rijkswaterstaat
17 Experiences in with mixing zones inRWS UNCLASS April 2011
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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18 Experiences in with mixing zones inRWS UNCLASS
Tracer simulations
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Model gebied L008
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19. Rijkswaterstaat
19 Experiences in with mixing zones inRWS UNCLASS
Waterbody properties from database
20 november 2015

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20 Experiences in with mixing zones inRWS UNCLASS
• Thank you for your attention!
Workshop 4 pm in Room Ambition.
Questions ?