Dwa_a_117_e

GERMAN DWA RULES AND STANDARDS

Standard DWA-A 117E Dimensioning of Stormwater Holding Facilities

2005 (English version in preparation)

- ABSTRACT -

Publisher/Marketing: DWA German Association for Water, Wastewater and Waste Theodor-Heuss-Allee 17 • D-53773 Hennef Tel. +49-22 42 / 8 72-120 • Fax:+49 22 42 / 8 72-100 E-Mail: [email protected] • Internet: www.dwa.de

DWA-A 117E

The German Association for Water, Wastewater and Waste, DWA, is the spokesman in Germany for all universal questions on water and is involved intensively in the development of secure and sustainable water management. As politically and economically independent organisation it operates specifically in the areas of water management, wastewater, waste and soil protection. In Europe the DWA is the association in this field with the greatest number of members and, due to its specialist competence it holds a special position with regard to standardisation, professional training and information of the public. The ca. 14,000 members represent the experts and executive personnel from municipalities, universities, engineer offices, authorities and businesses. The emphasis of its activities is on the elaboration and updating of a common set of technical rules and standards and with collaboration with the creation of technical standard specifications at the national and international levels. To this belong not only the technical-scientific subjects but also economical and legal demands of environmental protection and protection of bodies of waters.

Imprint Publisher/Marketing:

Printing (German original):

DWA, German Association for Water, Wastewater and Waste: Theodor-Heuss-Allee 17 D-53773 Hennef Tel.:

+49 (0) 2242/872-120

Fax:

+49 (0) 2242/872-100

E-mail: [email protected] Internet: www.dwa.de

Printed on 100 % recycling paper

© DWA Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V., Hennef 2005

All rights, in particular those of translation into other languages, are reserved. No part of this Standard may be reproduced in any form - by photocopy, microfilm or any other process - or transferred into a language usable in machines, in particular data processing machines, without the written approval of the publisher.

The scientific correctness of the texts, diagrams and tables does not lie within the responsibility of the publisher.

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DWA-A 117E

Foreword In water management it is generally acknowledged that runoffs caused by precipitation are to be avoided or reduced as far as possible already at the point or in the immediate vicinity of their production. If this is not possible temporary storage (holding) of stormwater and combined wastewater in stormwater holding facilities becomes necessary in many cases in order to protect the discharge systems from overloading or to limit their dimensions. In view of the investments which are necessary for the construction of runoff systems and holding facilities, a conception and dimensioning of holding facilities designed from economic aspects has great significance. With this not only holding tanks alone for retention but also large-volume sewer and surface water stretches, in line with the development objective for the surface waters, should be taken into consideration as holding facilities. The dimensioning, design and operation of holding tanks have, up until now, been regulated by Standard ATV-A 117E from 1977. Through the rearrangement of the Set of Rules and Standards the aspects of the design and equipping are covered in Standard ATV-A 166 [Not available in English] „Bauwerke der zentralen Regenwasserbehandlung und Rückhaltung“ [Structures for Centralised Stormwater Treatment and Retention], the operational aspects in Standard ATV-DVWK-A 156] [Not available in English] „Regeln für den Kanalbetrieb, Regenbecken und -entlastungen“ [Rules for Sewer Operation, Stormwater Tanks and Stormwater Overflows]. In 2001 the Standard ATV-DVWK-A 117 was republished and from this time regulated exclusively the dimensioning and the verification of stormwater holding facilities. For this, methods were introduced which correspond with today’s know-ledge and replace the dimensioning recommendations of the old Standard from 1977. In that Standard no standards with regard to dimensioning frequency and requirements on the protection of surface waters were defined. These result from the relevant Standards which are referred to in Chapter 1. The new methods take into account the fact that, from the superior water management aspect, ever more frequently a heavy throttling of area runoffs is demanded. For small throttle discharge rates, according to the methods of the old ATV-A 117E (1977), as a rule under-dimensioning resulted (ATV WG 1.2.9, 1998). In 2004 there was an editorial revision in particular with regard to the adjustment of the symbols to the requirements of Standard ATV-DVWK-A 198E, “Standardisation and Derivation of Dimensioning Values for Wastewater Facilities”. The methods recommended in this Standard as a rule require an increased expense in comparison with the previous procedures with the determination and procurement of the basic elements of calculation. So far as the dimensioning is not possible in accordance with the simple method described in the Standard and the verification process is to be applied using long-term simulation, increased costs for the procurement of precipitation data and for calculation occur in the planning phase. The application of the verification process requires the expertise of an experienced specialist. The higher requirements and costs in the planning phase are considered as necessary so that the dimensioning of holding facilities better satisfies the actual requirements than the previous dimensioning method. With this, for the operator, equally the risk of incalculable damage as a result of under-dimensioning as well as expensive over-dimensioning is reduced. These risks are generally, from a cost aspect, estimated as being higher than the additional planning expense.

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DWA-A 117E

Contents Foreword ................................................................................................................................................... 3 Authors ................................................................................................................................................... User Notes ................................................................................................................................................ 1

Area of Application ................................................................................................................. 5

2

Definitions..................................................................................................................

2.1

General Terms ............................................................................................................

2.2 2.3 2.4 2.5 2.6 2.7

Surfaces ...................................................................................................................... Precipitation ................................................................................................................ Runoff.......................................................................................................................... Runoff Simulation........................................................................................................ Volume ........................................................................................................................ Abbreviations (Symbols) .............................................................................................

3

Conception ................................................................................................................

4

Determination of the Volume of Stormwater Holding Facilities...........................

4.1 4.2 4.3 4.4 4.4.1 4.4.2 4.4.3 4.5 4.5.1 4.5.2

Methods ...................................................................................................................... Basic Elements of Calculation .................................................................................... Calculation Specifications ........................................................................................... English Simple Method ............................................................................................................ version in General ....................................................................................................................... preparation Area of Application ...................................................................................................... Procedure.................................................................................................................... Long-term Simulation .................................................................................................. General ....................................................................................................................... Technical Modelling Requirements.............................................................................

4.5.3

Results of Long-term Simulation.................................................................................

Appendix 1 Surcharge factor fS (comp. Table 2) ....................................................................... Appendix 2 Reduction factor fR (comp. Fig. 3) .......................................................................... Application of the simple method for SHT 1 ............................................................................... Application of the simple method for SHT 5 ............................................................................... Application of the simple method for SHT 4 ............................................................................... Results of the verification method .............................................................................................. Appendix 4 Application of the simple method for an upstream tank with combined sewer overflow ............................................................................................. Literature………………………………………………………………………………………………

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1

Area of Application

Standard ATV-DVWK-A 117E “Dimensioning of Stormwater Holding Facilities” is applicable in the area of the complete wastewater discharge between the property drain system and the surface water. The application of the methods in accordance with ATV-DVWK-A 117E can basically also take place within the area of the drain system or surface water, provided that the applicable standard specifications in the area of private property drainage, DIN 1986 “Site drainage systems”, or in the area of surface waters, DIN 19700 Parts 10-12 “Dam plants” are not infringed. The area of application within the ATV-DVWK-Set of Rules and Standards is shown in the flow diagram (see Fig. 1). The Standard presented here is applicable for individual stormwater holding facilities and complex stormwater holding systems as well as in both separate and combined systems. Existing stormwater holding facilities conceived according to other dimensioning methods should only be redimensioned in accordance with this Stan-

dard if there is information (considerations, observations, series of measurements etc.), that overloading leads to an unjustifiable risk of damage or if significant changes are carried out within the catchment area. For this, in each case, the original input data is to be checked. Standard ATV-A 128E is to be applied for the dimensioning of combined sewer overflow facilities in combined systems. The dimensioning of central facilities for stormwater percolation is regulated in Standard DWA-A 138E. Information is provided by the ATV Working Group 1.2.4. Report „Abflusssteuerung“ [Control of runoff] [not available in English]. Standards with regard to frequency of dimensioning can be taken from EN 752 and ATV-A 118E. Advisory leaflet ATV-DVWK-M 153 [currently not available in English] can be enlisted for requirements on water pollution control. Guidelines and recommendations for the construction, structural design and equipping of holding facilities are to be taken from Standards ATV-A 166 and DWA-A 138E as well as Advisory Leaflet ATVDVWK-M 176. Information and guidelines for the operation of holding facilities as part of a sewer system are contained in Standard ATVDVWK-A 156.

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DWA-A 117E

Fig. 1:

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Position of Standard A 117E within the DWA Set of Rules and Standards

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