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„Size matters.”
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Dimensioning of watercource protection facilities is a sophisticated
challenge, requiring in-depth knowledge
of local structural conditions and understanding of complex correlations.
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Watercource protection facilities are to be planned and dimensioned based on
the space available, criteria of discharge and information on geology and
tunnelling. Knowing all relevant data allows for making up a concept of an
optimised watercource facility and planning the implementation in detail.
All concepts of watercourse protection facilites by SEIBOLD-Messtechnik are
based on the standards of SIA (Swiss Engineer- and Architect Association,
www.sia.ch) and experiences,
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that SEIBOLD-Messtechnik was able to get from 50 projects in the past years.
Still the biggest challenge of dimensioning watercourse protection facilities
is the uncertainty of the inflow to be expected. A watercourse protection
facility will neither work satisfactorily in case of under-, nor oversizing.
A simple method for increasing the flexibility of the quantity of inflow to be
expected is having three settling ponds available whereof two are fed
continously as a rule.
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In various tenders settling times of up to 90 minutes are suggested. From our
standard of knowledge, this maximum value is taken from general terms of
reference of sewage tratment plants, that typically consider and respectively
do not consider parameters that might cause problems in other environmental
conditions. Sewage treatment plants usually do not face limitations of the
amount of space available, further deconstruction at the end of the
construction period usually is not an issue but has to be taken into
consideration in other types of applications, e.g. tunnelling projects.
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SEIBOLD-Messtechnik calculates the dimensions required based on the guidelines
of SIA. According to SIA Standard 431, as a rule of thumb for 20 minutes of
residence time within the settling pond one can assume:
volume required for discharge (m3) = inflow (l/s) + 20%
surface required** (m2) ~ inflow (l/s) x 2 **for discharging into a river
In general, coarse solids can settle in a short period of time, but airborne
particles (especially for clay or silt with grain size of 0.004 to 0.063 mm
according to Wentworth) cause problems to be coped by the use of flocculants.
The use of flocculants improves settlement by agglutination of solids of
smallest size by a factor three to five.
The concept for an ideal watercourse protection facility by SEIBOLD-Messtechnik
comprises equipment for dosing flocculants, for matching all criteria of discharge
of filterable and suspended solids even with unfavourable sloshing conditions.
Another requirement of an optimised watercourse protection facility is to avoid
pumps within the facility. As a consequence, ground basins and containers
should not be mixed within a watercourse protection facility. Having settling
ponds available as ground basis, neutralisation should be provided by the use
of concrete rings. Further, concrete rings should be located beneath the level
of the settling pond in order to provide settling and neutralisation without
electric current, too.
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SEIBOLD-Messtechnik und Projektentwicklug GmbH, A-1110 Wien, Grillgasse 51
Tel +43 1 332 00 60, Fax +43 1 332 00 60 44,
office@seiboldme.com
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