water concept kronsberg

Water Concept Kronsberg Part of the EXPO project

-Ecological Optimisation Kronsberg-

A company owned by the municipality of Hanover

ForewordWith the new suburb of Kronsberg, the Regional capital, Hanover, ispresenting a building project in which the World Exhibition themeof “Man – Nature – Technology” is being realised in a forward-looking manner. With the joint aims of ecological acceptability, andenduring and lasting development, the suburb is a veritable symbolof the local Agenda 21, to which the city of Hanover has committeditself.

In ecological terms, the water concept for the Kronsberg suburb isan essential component. It demonstrates that, even in buildingdevelopments covering major areas, adverse effects on the naturalwater economy can be avoided. In an area for 15,000 inhabitants,built at high-density to conserve both space- and building-resources,no more rainwater will be diverted than before the building tookplace, thus contributing greatly to prevention of flooding.

Without water, the world would be devoid of life. Continuous urbandevelopment means that we must be able to justify our behaviourwith water. On the Kronsberg, this is manifest in a number of ways.Water is used as a design element in public and private areas, as anartistic component; it shows drinking water economy programmesand is a part of teaching concepts in the schools and kindergartens.

The Kronsberg water project is being presented within the frameworkof the World Exhibition as part of the “Kronsberg – ecologicaloptimisation” project.

This makes it possible to present the idea for water drainage andurban water systems for lasting future urban developments to aglobal audience.

Hans Mönninghoff

Leader of the Council and Environment Manager

Herbert Schmalstieg

Lord Mayor

Fritz Tolle

Municipal Waterworks Chief Engineer

7

4

3

72 5

6

1

8 5

1

6

4

Local centre

Primary schoolQuarter Park

N13/14

M52

M53

M41

M42

N21

N22

N42

N43

M21

Kita I

Picture selection and project descriptionsee pp. 26-31Building Area Hanover Kronsberg

(General view)

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2

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Retention areas

Anecamp rainwater retention basin

Gulley-and-trench demonstration run

Water-dominated sloping roadswith solar-controlled watercourses

The Kronsberg environmental education concept

Water as an objet d`art

Water-dominated inner courtyards

Water as a sacred elementin the church centre

Local sportingfacilities

Freiherr-von-SteinSchool

Kronsberg School

Retention basinAnecamp

KUKA

Informationoffice

Treff-Hotel

High-levelwater container

HotelKronsberger Hof

Look-out hillNorth

Children`sday-care centre 3

Children`sday-care centre 2

Urban tramway

1Water concept Kronsberg

Contents

Foreword

1. Munipal building, country planning, drainagetaking account of flood precautions 2Ecological optimisation 3Forward-looking Municipal building 3Suburb with the short walks 3Country planning and outdoor leisure facilities 3Kronsberg as a social living environment 3Drainage 4

2. The building blocks of the water concept 5The “close to nature” rainwater system 6Water as an artistic component 6Drinking water economy in the apartments 7The rainwater concept for the primary school 7

3. Environmental matters 8The environmental education concept for the suburb 9The water concept for the Kronsberg junior school 9Qualifications for a career with water 9Information and advice 9

4. Planning and realisation in the public domain 10The starting point 10 - 12The overall concept 12Planning realisation 12 - 14Co-operation with the developers 15Demonstration run 16Building guidelines 17Experiences during building 18 - 19

5. Realisation on plots in the private sector 20Outline conditions 21Time-frame 22Authorisation procedure 22Realisation 23 - 25Brief description of some individual projects 26 - 31

6. CostsEconomic and feasibility study 32Economic situation 32

Impressum

2 Water concept Kronsberg

Municipal building, country planning, drainage taking account

of flood precautionsThe keynote of the UN conference in Rio deJaneiro in 1992, “sustainable development”,is synonymous with development which si-multaneously satisfies the needs of today’sgenerations, without endangering the needsof generations to come.This principle recognises that natural re-sources, as the basis of all life and economicactivities, cannot be used faster than theycan be regenerated, and may not be conta-minated with harmful elements to a greaterdegree than nature can handle.What continuous development means inconcrete terms, and how it can be achieved,is for each individual society to decide foritself.

The City of Hanover has committed itself tocontinuous development, with the local“Agenda 21”. With the Hanover 2001 pro-gramme, one which looks ahead to the city’sdevelopment beyond the year 2000, are ex-

amples of local negotiations devoted toachieving environmentally acceptable, la-sting and enduring development.

Indeed, as host city to the World Exhibition,Hanover is under a special obligation. Thus,to those EXPO-2000 visitors interested inthe realisation of the theme “Man-Nature-Technology”, the Regional capital Hanoverpresents the new suburb of Kronsberg as anintegral part of the EXPO programme “TheCity and Region Exhibited”.

The suburb stands for realisation of a conti-nuing urban development, where care is ta-ken of natural resources, but which respectshigh quality of life and demanding culturalaspects. It is not the aim to show a range ofhighlights, but the realisation of a forward-looking urban building project in life-size,where ecological, cultural, social structuraland urban planning considerations were de-veloped side-by-side, and can be transferredto other similar projects. In the forefront aretown and country planning, ecology, techno-logy, infrastucture and social facilities, andco-operative project development.

Competitions were sponsored, based onwhich a concept was developed for the newsuburb of Kronsberg, covering the suburb,the EXPO grounds and the adjoining coun-tryside. The new suburb of Kronsberg has aground plan in the form of a grid, with ave-nue-like streets, squares and green innercourtyards. It stretches like a wide ribbonfrom north to south, and connects the exi-sting suburb of Bemerode and the EXPOexhibition grounds.

In the long-term, Kronsberg is planned tohave 6,000 living units for 15,000 people.So far, about 3,000 of these units have al-ready been finished, and of them, more thana thousand are in use by EXPO 2000 exhibi-tors.

Aerial view of Kronsberg, 1999


Planning, organisation and realisation of thisenormous building project carries on simul-taneously at all levels:

Ecological optimisation

With the design of Kronsberg suburb, ac-count was taken throughout of all we knowtoday of ecological factors affecting buildingand living, and social aspects. Optimal de-sign of the living units, keeping waste to aminimum, public transport connections, cy-cle-paths, environmentally-aware site mana-gement during building, a “close to nature”water plan – these are all catchwords of theproject.

Foreward-looking municipalbuilding

The special feature of the project was theinfrastructure measures carried out simulta-neously right from the start. As the livingaccommodation was ready, so the infrastruc-ture was in place, and the suburb came aliveimmediately, and is green.

The suburb with the shortdistances

Short distances connect living, working andleisure. The new urban tramway only takes15 minutes to get from Kronsberg to thecentre.

Country planning and outdoorleisure facilities

Development of the countryside at the cityboundaries has for Hanover a very specialsignificance. Kronsberg is planned as a“garden city”. Lease-plots and allotments,parks in the various sectors and plantedpublic areas for recreation and sports areprovided for from the start. In addition tothis, there are to be numerous nature areasand open spaces, including an ecologicaland extensive agricultural establishment,including a farm with educational facilities.

Kronsberg as a social livingenvironment

Town of the future: that is the town as asocial and socially-acceptable living environ-ment, of high standard. Those who live the-re, or use the town, help to form its charac-teristics, and just as it grows, so does itssocial structure, according to its inhabitants’needs.

To realise the many different facets of theproject, a comprehensive structure for com-munications is essential. KUKA, short for theKronsberg Environmental CommunicationsAgency Ltd., was founded for this purpose,with the help of sponsorship from the Ger-man Federal Environment Foundation.

KUKA shareholders are the Regional capitalof Hanover, and the KUKA support group,which includes as its members the builders,electrical supply company, engineering andarchitectural offices etc., engaged in theKronsberg project, and which is open to furt-her membership.

The water concept is a constituent part ofthe EXPO project “Ecological optimisationKronsberg”, registered on 26.07.97. For theactual realisation of the project, it is KUKA’sforemost aim to achieve high levels of awa-reness of the environmental demands of theKronsberg with all operators and users. Atthe core, this means achieving changes ofperceptions, attitudes and behaviour. Interms of content it is all about energy, waste,water, ground, countryside and agriculture.

Sponsorship:Federal Environmental

Foundation

Projectsinitate, co-ordinate,

communicate

ShareholderSupport group

Regional capitalHanover

Shareholder Shareholder

Structure of the Kronsberg EnvironmentalCommunications Agency GmbH(KUKA)

Close to nature water concept

Forward-looking municipal building

Country planning


Drainage

The new Kronsberg estate displays alterna-tives of an enduring municipal development.

Hitherto used as farmland, the new Krons-berg estate will eventually cover 150 hecta-res (1,500,000 m2, or about 440 acres). Thisland use, a result of surface-sealing forroads, living and commercial buildings, hasunavoidable effects on the natural watersystem, as due to increased diversion ofrainwater or decreased opportunity for it tosoak away, there is increased incidence ofhigh peaks of water drainage and less for-mation of new ground water. For this reason,care in how water is dealt with is an essentialpart of the concept for an environmentally-intelligent urban development. Ecologically-oriented urban development and water sy-stems for new housing face the challenge ofre-orienting themselves. Technology todaynormally gathers rainwater in housing areasin a system of pipes and channels it as fastas possible into a lake. This technology mustnow be viewed with suspicion, with the highcosts associated with a pure water disposalsystem on the one hand, and the inherentdangers and disadvantages of formation offlood-water and reduction of ground-waterlevels, with their respective ecological impli-cations, on the other. Rain is very much lessto be regarded as a danger; its potential inurban development and design should muchmore be used to advantage. Occasion to turnthis new direction to practical account hasoccurred in recent years through the extra-ordinary high water levels in Germany. Thepossibility to reduce the causes of high wa-ter and to alleviate the effects is already athand in populated areas, in rainwater treat-ment, However, this will not solve the pro-blem completely, though a consistent appli-cation of the lessons in future new buildingareas’ water systems may be expected tomake a major contribution to stemming theincidence of flooding.

So far, however, there has been no realisati-on in a large new urban building project. Inthe suburb of Kronsberg, a water system isinstalled which enables rainfall to soak away– or be retained – in the area where it falls,and delays its delivery to the lake(s). Withthe gulley-and-trench system, natural geo-logical systems in Kronsberg are imitated.

The system ensures that formation of newground water, as well as water transport viaexisting channels, goes on. It makes a majorcontribution to ecological ground-water andflood protection. Thus the water concept ofthe Kronsberg shows the way ahead in urbanhydrology and drainage of built-up areas.The open rainwater gulleys become an im-portant element of urban design – they helpimprove the urban atmosphere, moderatethe temperature, and create leisure areasfor the inhabitants.

Situation 1994

Variant: standard rainwater drain

Variant: gulley-and-trench system

Water systems – the balance

Evaporation304 mm/a

Drainage14 mm/a

Percolation256 mm/a

Evaporation264 mm/a

Drainage165 mm/a

Percolation145 mm/a

Evaporation268 mm/a

Drainage19 mm/a

Percolation287 mm/a

Street-laid gulley and

trench system


The water concept for the Kronsberg suburbcomprises the two main elements: the tech-nical, building measures and the communi-cations concept. With the assistance of di-verse communications instruments, thecontent of the technical measures are pas-sed on, to encourage a better, wider under-standing of the role of the vital element,water.

Building blocks of the

water concept


The “Close to Nature”rainwater system

For the water system, the Kronsberg settle-ment is of particular importance, as the newgroundwater formation rate at 194 mm/a issubstantially higher than the Hanover aver-age. The aim of the “close to nature” rain-water system is as far as possible to havethe same natural drainage available afterbuilding as existed before. In the whole ofthe settlement, in principle, decentralisedwater retention areas are planned. As muchrainwater as possible will be retained onprivate and public ground and be allowed tosoak away, and only limited amounts will bedrained off. This will be achieved by usingthe functional elements:

Gulley-and-trench systemSluiced channelsRetention areasRainwater reservoirsOutfall ditches

Water is channelled into green-planted gul-leys and held there. It filters through a layerof humus into the ground store (the trench)which is filled with gravel, being cleaned inthe process. It soaks away from the trench.Excess water is fed, much delayed, via asluiced shaft into the sluiced channel andthence fed to the retention areas and thegreenery. These form the basis in the streetsand planted areas for long-term living withrainwater in the cities and towns of the fu-ture. The numerous water surfaces in thegulleys will encourage evaporation, influ-ence the climate in a positive fashion andreduce the formation of dust. The retentionareas, laid out like parks, and measuring upto 35 m wide, along with the rainwater re-servoirs, help protect against flooding, ashigh rainfall will be fed gradually into thedrainage ditches. This concept only increa-ses the outfall and seepage marginally, andas a result, original conditions are largelypreserved, whereas conventional rainwaterdrainage would increase the outfall by afactor of 10.

Water as an artistic compo-nent in the “Quarter Parks”

The two “Quarter Parks”, each measuring10000 m2, have special significance for re-laxation in the suburb as the “green heart”.Each will be individually landscaped. In thenorthern park, rainwater sound openings willbe installed, so that the pattering of rain canstill be heard after the rain has stopped.

Boxed-in drain with sound opening

The sloping street

Weinkampswende

Gulleys at Ellernbuschfeld

The sloping street Feldbuschwende

Retention areas at the foot of the slope

Rainwater reservoir Anecamp


Drinking water:domestic economy measures

Of the daily usage of 142 L of drinking waterper person in Germany, most runs throughthe shower, bath, wash-basin and toiletstraight to the drains. Only about three litresare used either for drinking, or for cooking.As water provider, the Hanover MunicipalWater-works is aiming to reduce that figureto 100 L per person. The saving will beachieved by a full programme of drinkingwater economy measures. In the individualhouseholds, in the expansion phase, possi-bilities for the economic use of water havealready been identified. Economy aeratorshave been installed in wash-basins. Thesereduce water-consumption greatly, althoughit is barely perceptible. Flow-limiters andflow stabilisers are also effective. Within theframework of the Regional capital Hanover

and KUKA energy economy programme,each household will receive two aeratorsfree of charge. These economy measureshave had their effects in other directionstoo; the pipes for drinking water are smallerthan usual, and are laid exclusively for drin-king water and not, as is more often thecase, also for fire-fighting requirements.

Cleaning

Watering gardens

Washing clothes

Toilet

Other

Dishwashing

Baths, showers

WashingDrinking, cooking

6 l

18 l

46 l

7 l

9 l

40 l

10 l

3 l

6 l

14 l

22 l

6 l

7 l

35 l

8 l3 l

Dri

nk w

ater

usa

ge t

otal

: 14

2 l

Dri

nk w

ater

usa

ge t

otal

: 59

lCo

mm

erci

al w

ater

usa

ge t

otal

: 45

l

Drinking waterconsumption

TODAY

POSSIBLEdrinking water

consumption witheconomy technology

and use of commercialgrade water

3 l

3 l

The rainwater conceptfor the primary school

In the Kronsberg primary school, water hasa central significance. All the rainwater fal-ling on the school plot is stored, fed througha seepage and collected in a tank. Open,surface rain-water ducts, retention and see-page areas in the school grounds are usedas important design components, creatinga habitat for plants and animal life in theschool’s gardens, and recreation areas. Thesloping school roof is extensively planted,and rainwater thus flows off more slowly.The rainwater collected is used either asindustrial water for toilet flushing, or in theschool garden. Integrated rainwater usagemakes it possible to save annually about550 m3 of drinking water. In the school itself,not only is the technology for saving wateravailable; teaching how to use and conservewater is given special emphasis.

Water usage in German

households in litres

per person per day

Kronsberg primary school


Environmental communication

Communication concept:Water as part of environ-mental communication

The communication concept water is part ofthe environmental communication concept.Its target is to promote the enduring de-velopment at the Kronsberg via instrumentsof communication. Man, as the planner, buil-der and above all as user and inhabitant ofthis suburb, stands in the forefront of envi-ronmental communications concepts. Envi-ronmentally-friendly technology must beaccepted – and to an extent understood –so that the joint aims of endurance and en-vironmental protection can be truly realised.Environmental communication makes useabove all of the instruments of information,publicity, advice, education and qualificati-on. Every group connected with the suburbwill be reached with the communication con-cept water.

These include:

the residentsbuilding sponsors and ownersthe building artisans and craftsmeneducationalists and consultantsvisitorsspecialists(scientists, architects, engineers)the specialist public and media

Information and advice

Exhibition

An exhibition on environmental projects inthe suburb is on view in the suburb’s centrallibrary. The significance of water to all oflife, and how it is treated in the suburb, isvisualised there.

Information boards

In various places in the suburb, boards arelocated, which draw particular attention toone or other aspect of the water concept.Simple, easy-to-understand sections of theoverall system are presented.

The magazin „Kronsberg aktuell“

The magazine appears six times a year. Itreports on the latest developments in thesuburb, and occasionally on matters of par-ticular importance, e.g. water.

Specialists and residents`promotions

Subjects of special interest to residents aredealt with in seminars. Alongside themessuch as energy, water themes are becomingincreasingly popular.


The environmental educationconcept for the suburb

The environmental educational concept islaid down as an essential principle, so thatthemes will be continued with no break fromkindergarten through to junior school. Theessential element is behaviour with naturalresources. This means that water takes on arole of major importance.

The water concept for theKronsberg primary school

The example of the rainwater concept of the4-class primary school shows how the “closeto nature” idea of handling water can con-tribute to teaching the children about theirenvironment. Learning material on the the-me of water is collected in co-operation withthe school teachers. The environmental sub-jects the children learn include water circu-lation, as exemplified by their part of town;the importance of drinking water; water –the habitat; wetlands; and the care of see-page areas.

Qualifications for a careerwith water

The vast area with total coverage realising a“close to nature” rainwater system makesthe suburb of Kronsberg an ideal subject foreducational study for career qualificationsfor students of hydrology. Knowledge can begained here on a practical basis, within theframework of education and further training.


Planning an realisation in the

public domain

The starting point

The suburb was to have a consciously urbancharacter, with appropriately-high buildingdensity. The building structure follows the4 - 6% fall of the west slope of the hill on theprinciple of height and density reducing to-wards the crest of the Kronsberg. Thus, fromwest towards the east, there are three di-stinct zones of buildings with different num-bers of floors, building density and buildingstyles. The west of the suburb, alongsideOheriedentrift and the urban tramway, therewill be a 4 1/2-floor-apartment block in rowsand blocks, the highest buildings and thusthe highest surface user. In the centre, 3 1/2-floor buildings in rows, with some individualbuildings, will predominate, while on theupper edge of the development there willonly be 2 1/2-floor terraces.

The water system in Kronsberg is very sen-sitive. It was clear from the beginning of theplanning that the Kronsberg could only bedeveloped if a water conservation systemoptimally tuned to the area were to be used.

Planning area Kronsberg


The demands of thewater system

Since it was always planned to build on theHanover Kronsberg, the planning decision of1971 was that a maximum discharge of 200L/s should be permitted from the drainageditches into the Landwehrgraben. To avoidexceeding this amount, following the courseof the drainage ditch, rather like pearls on astring, 3 rainwater reservoirs were planned:

So far, it has not been possible to build theOhe reservoir due to land ownership pro-blems. The Hasenkamp basin is already wor-king at absolute capacity. Only the Anekampbasin has any reserve capacity left.

KeyWater areas/rainwater reservoirs

Building areas/traffic circulating areas

Trees, hedges

green areas, wooded areas

Main access roads

Urban tramway

Rainwater reservoir Anecampat the foot of the Kronsberg

Rainwater reservoir Oheto the south of the main road B 65

Rainwater reservoir Hasenkampdirectly before the outfallinto the Landwehrgraben

Rainwater reservoir Anecamp


The hydro-geologicalstarting point

Initial hydro-geological studies in 1983 car-ried out by the Hanover University Instituteof Hydrology (Prof. Sieker) concluded thatconventional building on the Kronsbergwould have a disastrous effect on the groundwater system.

As a result, the Kronsberg development wasput “on ice” for the time, but with the star-ting gun for the Hanover World ExhibitionEXPO 2000, it was decided to examine thehydrological conditions of the Kronsbergmore closely, and to quantify them accura-tely.

Directions of flow of groundwater were ob-served once more by the Institute of Hydro-logy in 1992 (Prof. Mull): for this, the fewmeasuring locations available for groundwa-ter were reinforced by a further 18 bores.The effects of a conventionally-drained de-velopment on the Kronsberg on the hydrolo-gical situation were assessed as follows (seetable right):

Concept

To forestall the prognostications of the sur-vey, the following specifications were incor-porated into the explanation of the applica-tion for change of use for the Kronsberg in1993, for the building plans described.

For this reason, a drainage concept had tobe worked out for the Kronsberg develop-ment, which would guarantee a minimum ofdisruption to the natural water system. Thishad to be designed so that the drainage forthe complete area was as close as possibleto that which it had been before develop-ment. This resulted in a figure of a one-yearmaximum high-water of 3 l/(sxha). This va-lue was then used as a benchmark for thewhole Kronsberg development.

The earlier survey results suggested delibe-rately allowing falling rain to soak away.However, the geology of the Kronsbergmakes this difficult. The subsoil is mainlypoorly permeable calcareous clay with per-meability factor:

kf = 3 x 10-6 m/s bis 10-8 m/s.

It was the idea from the start to slow downthe rain’s reaching the nearest drain. For thisreason, the concept had to include a combi-

Seelhorstper planning variation: i.e. according to proportion sealedlowering by 20 to 30 cm

Mastbrucher Holzper planning variation: i.e. according to proportion sealedlowering by 50 to 100 cm

EilenriedeReduction in the underground drainageReduction of basic outflow from Landwehrgraben, with thepre-programmed consequence of a drop in the groundwater level

Open Ditch(can no longer be compensated by close-to-natural measures)Increase of high-water flows when rain falls andreduction of low-water flow during dry weather

nation of soakaway, de- and semi-centralisedstorage and delayed outfall. The result wasa close-to-natural rainwater system withboth above-ground and underground com-ponents as parts of the solution.

Planning realisation

To maintain the grid layout specified for theurban development’s ground form, the gul-ley-and-trench system proved to be themost suitable.

Because of the size of the area being de-veloped, with its extensive surface sealing,the “gulley-and-trench” system on theKronsberg is the actual object of the rese-arch project “Rainwater handling, HanoverKronsberg” (flood precautions).

In the streets in the new development, theonly gullies to be seen will be at roadjunctions. Above ground, at the roadsides,between pavements and parking spaces,there will only be 30 to 40 cm deep, green-

planted, gullies to be seen, which will gatherrainwater on the surface.

As it soaks through the gulley floor (30 cmtopsoil), the surface water is cleaned. Thewater soaks through a further, gravel-lined,ground reservoir, called a “Rigole”, ortrench. As the water seeps through to thetrench, the water level here rises gradually.

The water out of the trench reaches thesluice through a drainpipe. It can only es-cape from the sluice through a small pipeadmitting 3 L/(sxha) into the rainwater drai-nage network. For this purpose, the munici-pality developed a specially-designed shaftwith a built-in sluice. Water reaches thedrainage network via the sluice-shaft. Thisis sized according to the sluice, and is loca-ted, as in traditional rainwater drainage sy-stems, in the streets connected.

By comparison with the natural drainagebehaviour, the lying time of the water storedin the trenches is simply extended. Thus thewater flows only very slowly away from the-

Groundwater flow behaviour

marl-limestone

Kronsberg

limestone

ditch ofLandwehr

quaternarydepositions

clayclay-marl

boulder clayditch ofWietze

clay-marl

marl-limestone


se gulley-and-trench elements and the na-tural drainage behaviour that existed beforethe development can be copied, in otherwords, the rainwater basin at Anecamp andthe ditches will be no more seriously loadedthan before.

Over 5.5 km of roads (=about 3 m.) thegulley-and-trench system has been laid onboth sides of the road, because of their lay-out. The city is carrying out a project which,for its size and the pressure of time, isunique.

The gulley-and-trench system was laid downfor public traffic areas at the building plan-ning stage. It will be laid parallel to the roadin green strips between the pavement andthe parking spaces. There is a strip of 2.0 mgross width available here. Surface area re-quirements of an average 10% of the ad-joining area is adequate. As far as rain mea-surement is concerned, the channels stackonly about 16 cm.

To achieve large and even coverage, thebases of the gullies and trenches need to behorizontal. Cascades cannot therefore beavoided in streets leading uphill. If duringtorrential rain the gullies and trenchesshould be full, the water will flow via anemergency overflow on the sluice shaft di-rect into the public drainage system.

The gulley-and-trench system is being usedto even out the formation of new groundwa-ter and the outfall of drainage to the originallevels.

Rainwater dwell time in the gulley:1-year max. rainfall (T=15 min)t = about 1 hour5-year max. rainfall (T=15 min)t = about 2 hourscan vary considerably, according to the ar-rangements of lead-ins

Rainwater dwell time in the trench:1-year max. rainfall (T=15 min)t = about 16.5 hours r 15,15-year max. rainfall (T=15 min)t = about 29.3 hours r 15,o,2

Gullies are dimensioned for 1-year max.rainfall, the trenches for 5-years max. rain-fall. The newly-laid water retention areas atthe foot of the hill west of the main roadsOheriedentrift and Kattenbrookstrift and thetram-tracks and the Anecamp reservoir, re-built due to the tramway extension, then asa “close-to-natural” catchment area, are alldesigned for ten-year maximum rainfall.

The 18 to 35 m wide occasional catchmentsare laid out as parkland. They serve to holdrainwater from the main roads Oherieden-trift, Kattenbrookstrift and Wülferoder Stras-se, taking the outfall from the sluice net-work.

The open ditch at the foot of the Kronsberg,still runs in a regular channel. Creation ofedging strips will allow the stream to de-velop naturally. In this way, speed of flow

will reduced. For this, adequate edging hasalready been created over some 500 m. The-se serve at the same time as protection forthe water against the surrounding use aspasture. Apart from crossing and inlet buil-ding works, no further works are planned.For the residents, an experience, and a re-creation area, is taking shape at their frontdoors.

Flow scheme of a sloping street

(Photo: Feldbuschwende)

Gulley-and-trench system –section through drain-gulley

Water concept in the housing area

back-to-nature for the open ditches

road with a downhill slope (Feldbuschwende)

road with a downhill slope (Weinkampswende)

natural retention areas

rain retention reservoir Anecamp

Oheriedentrift

retention area

open ditch

gulley-and-trench system

rainwater reservoir

sand filter layer

absorbent material

trench

drainpipe

gulley inlet

cascade

parking area

pavement

slop

ing s

treet


Rainwater in the slopingstreets and the retension areas

The sloping streets Weinkampswende andFeldbuschwende present the water themein a very special way. They play an outstan-ding role in the handling of the Kronsbergwater system, because the water is not allo-wed to soak away in trenches for functionalreasons, but forms an integral theme of itsown in town design.

Rainwater falling on blocks of buildings toeither side is fed to 12 to 30 m wide avenueswith trees, bushes and paths, where thewater is channelled into above-ground stre-ams.

In this way there are:

permanent pondsgullies which occasionally carry waterseating arrangementsrunning streamsnatural pathways

Public fountains, lakes, seats around smallponds and water games all give good reasonsfor stacking water in sluices. All these waterelements help create a more healthy climate,because water helps to moderate tempera-tures and reduces dust considerably.

With the help of photo-voltaic pumps, rain-water is returned time and again to the topof the street, so that it can be seen to flowin the artificial channels, when it has notrained for a long time.

The retention areas at the foot of the hill arealso designed to give the future residents avision of the importance of water, actuallythe above-ground handling of water. Theresidents can enjoy slopes covered with ve-getation and the watersides as nearby re-creational areas. The retention areas are

deliberately designed to allow the water tobe enjoyed. They have a park-like character,and positively invite one to while away sometime there.

At the start of EXPO 2000, about half ofthese areas are complete. The other retenti-on areas are as yet temporary and in accor-dance with current water storage require-ments. They will be finally designed andcompleted at the conclusion of EXPO 2000.

The sloping street

Weinkampswende

Photo-voltaic plant on the slope of Weinkampswende

Retention area at the foot of the slope

Weinkampswende - rainwater channel

Feldbuschwende - sluice element


Co-operation with thebuilding sponsors

The original intention was to develop thewhole project including services and connec-tions through investors and building spon-sors. However, in view of the situation in thehousing market in late 1996/early 1997 andecological considerations, the city of Hano-ver and the State of Lower Saxony felt obli-ged to relax the occupancy conditions forthe apartments and to offer suitable spon-sorship. Only in this way was it going to bepossible to get the project on its way by thestart of the World Exhibition EXPO 2000.

For development, there remained within theprojected building area only one fairly largearea, covering about nine clusters, to bedeveloped by the Immobilien Developmentand Holding Company, Lower Saxony (IDBKronsberg) – hereinafter designated “IDB”.A development contract was concluded ac-cordingly.

When the rainwater concepts were put intopractice, different solutions were adopted asbetween the IDB area and the remainingresidential areas of the LHH.

Consequently, the individual gulley-and-trench elements of one section of road onone side of the road are connected in a formof “series” switching.

This means that now, all the rainwater fromone section of the road on one side is ledvia the last downhill sluice shaft of the gul-ley-and-trench system into the rainwater

channel (sluice outfall channel).Through joining the areas to be drained it isnecessary to fit a larger opening (14 mm) tothe sluice.

open-air rainwater retention areas

Development areas(as at May 2000)

Hanover Municipal Waterworks

(completed)

Hanover Municipal Waterworks

(planned)

IDB (completed)


Demonstration run –Gulley-and-trench system

To gain additional knowledge and experi-ence to enable the planning to be optimisedand make the building more practicable, afull-sized demonstration run was construc-ted. The following questions in particularwere to be examined:

functional reliability when draining through small sluice openings

optimising the gulley leads to suit the inclined plane of the

building landsimulation of rainstormsexperience for the building work

Within the framework of the research project“The rainwater system of Hanover-Krons-berg”, sponsored by HM Bau, the demon-stration run was observed by scientists fromHanover University.

Based on the flooding attempts on the de-monstration section, theoretical starting-points for water leads, gulley soakaway anddrainage via small sluice openings could bestudied in virtual practice. This made thedevelopment of improved designs possibleat an early stage.

As an example, the first design of gulley leadpermitted a proportion of the surface waterto run straight past the gulley. Not to havediscovered this until completion of buildingof the first roads would have been fatal re-garding the general credibility of the project.

Experiences for the building work

Excavation and roadworks and MRS workinterconnect in such a manner that it isimpossible to nominate two different con-tractors to do the work. Civil engineers andthe Municipal Water Authority thereforedraft specifications for construction of roadsjointly.

Image / credibility

Active co-operation with Hanover Universitydid much to reinforce credibility and to gainthe trust of other town planners and withthe developers even in the somewhat un-usual plans for handling the rainwater sy-stem.

The fact that the demonstration run was thefirst visible building operation (drains youdon’t see...) encouraged a feeling of opti-mism in the town planners in regard to ouractivities.

If the demonstration run led to a certainsolidarity of those involved from the city, itsvalue cannot be estimated in terms ofmoney. It certainly led to a better under-standing, and lessened the tendency to lookfor the snags. It also meant that it was notrepeatedly asked that justification be produ-ced.

The demonstration run

Rainfall simulation on the demonstration run

Gulley cascades

Gulley lead with ballast packing


Building guidelines

Two engineering offices were engaged asconsultants both in planning phases andduring the actual building.

To formulate the most important elementsof the building of the gulley-and-trench sy-stem on the Kronsberg development, and tomake quality control easier, a building hand-book was assembled with tabular details andan explanatory text. It helped all those in-volved in the project in specification, tende-ring and building supervision, and was forinformation of the builders carrying out thework.

Specific help was given in thefollowing areas:

Specification for the selection ofmaterial, with hints as toinstallation and description of testcriteria for the suggested materials.

Building sequence description withhints for important basics for buildingthe gulley-and-trench system.

Quality assurance concept, coveringtraining of the building firms andplanners; timetable or sections forpartial handover, and functionaltests.

Experience during building

Since autumn 1998, installation of the gul-ley-and- trench system has been proceedingboth in the area for which the private devel-oper is responsible, and in the area beingdeveloped by the regional capital of Hano-ver.

The following statements are restricted ingeneral to experiences gained in the areabeing connected by the Hanover MunicipalWater Company.

It is a first report on conditions; it is as yetmuch too early to make any general com-ment on operational reliability or on costsof operation.

Specification, tendering procedure

Due to the close interconnection of the workto install the gulley-and-trench system withthe road-building, it was clear to all partici-

pants from an early stage that all this workshould be in the hands of one building com-pany only. Otherwise there were going to bemajor problems above all in scheduling thework, maintaining finishing dates and gua-rantee demarcation questions to be expec-ted.

For this reason, for every building lot thespecifications were drafted for the gulley-and-trench system in a joint operation withthe office of the city of Hanover’s civil engi-neer, which is responsible for road construc-tion and development in this area.

Sluice shaft

The sluice shaft used in conjunction with thegulley-and-trench system on the Kronsbergdevelopment must be capable of performingthe following functions:

Accepting the sluice element.Outfall control is through a holedrilled to 8 to 10 mm diameter,according to area connected.The function of emergencyoverflow is also ensured; excesswater can run into the verticalpipe in the body of the sluice.

Inlet from the drain into the shaftis closed by submerged trap to preventingress of floating particles andoil into the trench.

Sufficient large openings in theshaft cover allow water to overflowout of the gulley if this cannot soakaway fast enough, e.g. in torrentialrain.

Very high safety in operation ofthe complete system.

Easy maintenance of thecomplete system.

Use of standard building components.

Sluice shaft

grating

maximum water level gulleygreen-plantedgulley

top ground layer

filter

trench

drainpipe

filter insert

overflow

normal waterlevel

sluiceopening

sluice element

submerged trap

connection tothe rainwater

drainagechannel


Design of the gulley inlets

To prevent the surface water running by thegulley inlets because of the gradient on theKronsberg, the gutter paving was loweredby 4 cm in the inlet area. This was to becatered for in the inlet design.

Design of the gulley

After the first gulleys were seeded withgrass, it was clear there were going to bemajor problems with the planned vegetationplanting and the stability of the slopes. Dueto the amount of building work being carriedout simultaneously in the immediate vicinityvery serious damage was being done to theslopes. Consequently it was from the outsetdecided to carpet the gulleys with ready-grown turf. This step, admittedly rather moredifficult in the first stage, proved to be a farbetter protection for the gulleys against de-struction and erosion.

To protect the gulleys against being runover, the kerbs chosen were those familiarin the city. The gulley inlets were simplydesigned as blunt, 52 cm. wide interruptionsin the kerb, with the intervening space filledwith coarse gravel. The design of the gulleyinlets as used up to July 1999 could not becalled entirely satisfactory. Weaknesses wereapparent in the loading of the individualgulleys due to long distances (6 m) betweenthe inlets and the gravel beds in the inlets.

The kerb-breaks, together with the sunkenguttering, form a good protection for thegulleys against being run over. However,practical experience when mowing the gul-ley-strips on the demonstration run haveshown that the loose, coarse gravel in theinlet area poses too much potential danger. Accordingly, the gulley inlet was thoroughlyre-designed, and since July 1999, instead ofthe gravel bed, a cast concrete form hasbeen used as gulley inlet. The form de-veloped for the Kronsberg is similar to one

which has been installed in the Rummels-burger Bucht building project in Berlin.

By consistently following the establishedprinciples of rainwater handling, instead ofever faster disposal, water speeds are goingback to a natural state. With the gulley-and-trench system, and its features of so-akaways, storage and delayed outfall of rain-water, in spite of the large newly-sealedarea, a natural rainwater flow is being achie-ved.

1 Building sequence– 6

The new gulley inlet

1


2

4

5

3

6


Realisation on plots in the

private sectorIn the Kronsberg project an overall waterconcept, covering private plots and publicopen spaces, was realised. The aim was toachieve a water balance after completion ofthe project corresponding to that in placebefore it was started.

For the public areas, the gulley-and-trenchsystem was adopted by the Municipal WaterAuthority, with retention areas.

The private plots, which cover an area ofabout 46 hectares (some 112 acres) weresub-divided and sold to various investors.

Realisation of the water concept was subjectto keeping to various conditions, both in theprivate and in the public areas. When thesoakaways were designed, the water was tobe made enjoyable in as many ways as pos-sible. And the drinking water economy mea-sures included, rounded off the design ofthe suburb.


Framework conditionsTo attain the above objectives, binding agree-ments were made on various legal bases:

1. The building plan

Rainwater from sealed surfaces had to bechannelled into a gulley-and-trench system,there to soak away or be fed at a controlledrate into the public drainage system. Thesystem brings together decentralised reten-tion, as high a level of seepage as possibleand strictly-controlled outfall into the publicdrains. Ground conditions at the Kronsbergwhere there is an average permeability of1 x 10-7 m/s were taken into account (Plan-ning Team – Water, 1995). Exceptions werepermitted, as for example where all the rain-water falling on a plot could either be allo-wed to soak away or be led in a controlledflow to other areas.Minimising measures, according to naturepreservation law, were also imposed on plotowners, who were obliged to pave parkingand access areas with permeable slabs andto plant roofs of underground garages notbuilt over and roofs with an inclination ofless than 20° in certain areas of the suburb.

Parking place with permeable paving

2. Drainage Regulations for the Regio-nal Capital Hanover of 16.05.1991.

Permitted rainwater outfall and thus thecontrolled flow was laid down based on theretention of rainwater regulations. Allowedwere 3 L/(sxha), this value related to thebuilt-up and sealed areas as specified by thePlanning Team, water (1995). Undevelopedareas were included, according to DIN-EN725-4 (11.97) if, due to ground impermea-bility and slope, rain-water would be led intothe soakaway.

To assess the soakaways, paper A138 of theDrainage Association (1.90) was drawnupon. Ever since 1996, on private land, insuitable framework conditions, soakaway ofrainwater always takes precedence over fee-ding direct into drains. Drawing on the abovepaper was worthwhile.

3. Lower Saxony Water regulationsof 25.03.1999

After examining the permeability of theground, the water authority stated that nolegal authority was required to allow rain-water to soak direct into the groundwater.

4. Use of environmentally-neutralmaterials on Kronsberg,

e.g. not using PVC pipes for water drains.The specifications formed part of the plotsales contracts.

There were also technical reasons deman-ding exact and precise co-ordination bet-ween all concerned. These included for ex-ample:

1. The position of the connections was ex-clusively permitted in the plot accessareas, and not in the area of the inlet tothe gulley-and-trench system. Further-more, no connection was planned intothe site access road Oheriedentrift / Kat-tenbrookstrift, as it had already been sur-faced.

2. Planning of common soakaways for thehousing terraces, otherwise a sluice drainadequate for the plot would hardly bepracticable. Here, no actual specificationcould be laid down, so a simple suggesti-on was made.

3. The comparatively steep slope of the buil-ding land, with particular effect on thedesign and planning of the soakaways.As gullies and trenches normally have to be built horizontally – i.e. withoutslope – here, there were stepped systemsand additional stacking regulators neces-sary. Yard drainage and rainwater chan-nels lying below the flood level of thesystems must be protected from overflowof rainwater. There were frequent pro-blems with soakaways located centrallyin yards when draining lower-lying pavedor otherwise sealed areas.

4. The building schedule was extraordinarilytight, as it was necessary to have all buil-ding works completed in the 2 1/2 yearsbefore EXPO 2000 began. Thus the exactsequence of building, the installation ofdrains, road construction etc., was laiddown, and had to be maintained. Everydelay or alteration would result in sub-stantial problems.

There were no other specifications in theplot sales contracts. So the investors hadwithin the above legal framework every free-dom to size, design and construct the so-akaway system as they wished, within thebounds of today’s technology.

In the realisation, the above specificationswere to be assessed and respected accor-ding to legal responsibility. The soakawayswere the responsibility of the Municipal Wa-ter Company, the minimising measures fornature protection and use of environmental-ly-neutral materials were the province ofthe Environmental Protection Office.

Pergola

Carport with roof planting


Time frameThe first planning documents for realisingthe water concept on the private plots in thenew Kronsberg suburb were put forward inautumn, 1997.

In March 2000, the date of this report, theplanning concepts for rainwater disposal for43 building lots were to hand. Meantime, 40of the drainage systems requested have be-en examined and passed.

Building of the soakaways began in the se-cond half of 1998. Diagram 1 reflects thestate of building in March 2000. 14 of thesoakaways were by this time complete, anda further 5 were partly complete, so that atotal of 19 could be included in the overallassessment.

Authorisation procedureComprehensive consultation with the plan-ning offices on framework conditions wasnecessary. Detailed co-ordination betweenthe various offices of the city administration,planning offices and builders (private sector,public sector and road construction) wasanother essential feature towards carryingout the project under the existing technicalconstraints with the precisely laid out sche-dule to which it was essential to keep.

Authorisation was given in each case as de-tailed specifications of the drainage systemswere fulfilled. Other systems than the gul-ley-and-trench system were, however, per-missible. This was the background:

During authorisation procedure, a numberof investors requested to be allowed to usesystems other than the gulley-and-trench.These requests were generally linked to aparticular design wish for the seepage sy-stem, internal cost-analyses or usage con-flicts of the areas in question.

As long as the alternative systems fulfilledthe basic requirements of the building plani.e. decentralised retention with optimumseepage and strict control of flow into thepublic drainage system, as in the gulley-and-trench system, these would be appro-ved. This also avoided right from the startthe risk of legal challenges, which wouldprobably have delayed the Kronsberg projectuntil EXPO in any event.

A soakaway forms part of all drainage sy-stems. Portions of one plot may be attachedto different systems. A positive result of theauthorisation of soakaway designs otherthan the gulley-and-trench system, was theavoidance of a highly-formalised appearan-ce, in favour of numerous attractively-de-signed fixtures (Diagram 2).

In two cases use was made of the “exception”to the building plan, to feed outfall rainwaterin a controlled way into other areas, in thiscase the public rainwater retention areas, forseepage. On one plot, which according tothe building plan had a permitted buildingfactor of 1.0 and thus was to be totally builtover, the rainwater is to be temporarily stac-ked in a channel then fed under control intothe public system. In the second case, asmall proportion of the rainwater (balconydrainage) was to be fed to a retaining channel,because on account of the building’s location,it would have had to be pumped uphill, ex-pending unnecessary energy, to feed it intothe soakaway.

Diagram 2

Soakaway systems

pond +seepage basin

(1 system)2 %

pond + gullies-and-trenches+ trench

(2 systems)5 %

pond + gullies-and-trenches+ cistern(1 system)

2 %

retention channel(1 system)

2 %

trenches + gullies(4 systems)

9 %

trenches+ gullies-and-trenches

(2 systems)5%

seepage basin+ trenches(3 systems)

7 %

pond + trenches(2 systems)

5 %

seepage basin(3 systems)

7 %

gullies-and-trenches(7 systems)

16 %

trenches(16 systems)

38 %

seepage basin+ retention channel

(1 system)2 %

Diagram 1

Building situation in March 2000

Partly completed andincluded in the

evaluation:5 systems

(12 %)

Completedand included inthe evaluation:

14 systems(33 %)

Not completedor not yetavailable:

24 systems(55 %)


RealisationIn the suburb of Kronsberg, a number ofdifferent soakaway systems have been plan-ned. In general, the building of the systemshas corresponded to the drainage conceptwe put forward.

There were departures from plan in somecases in provision of inspection shafts andsettling or pre-purifier arrangements. If aninspection shaft is not provided, under-ground soakaways such as trenches cannotbe maintained. In addition, when settlers orpre-purifiers are not provided before thetrench, the soakaway’s performance is ad-versely affected which may lead to earlyfailure of the equipment and thus to an ex-pensive replacement of the whole systemby the plot owner. The sluice can also beaffected by inflow of coarse matter, causingblockage and thus making the system over-flow.

On some plots, it was discovered that someof the rainwater falling on sealed surfaceswas flowing above ground into the publicstreets. This fault was mostly to be foundaround the entrance areas to the houses,and in the plot accesses.

There are also problems caused by the lackof, and limited capability of, the necessarywater-stacking regulator equipment. Becau-se of the inappropriate depth of fitting someof the sluices, and the fact that there is noaccess to the shafts, the settings of thesluices are impossible to check.

Limited functioning of the sluices is causedto a large extent by dirt in the openings, orthe mechanism itself. This is often to betraced back to mortar scraps or earth fromthe building stage.

To ensure controlled flow of rainwater fromthe plot into the public drains, these pointsmust also be corrected.

The average ground-seal figure for the plotsis 56%. Diagram 3 shows the division bet-ween roofed areas and sealed ground, i.e.paths and parking spaces etc.

In calculating the roofed areas of the indivi-dual plots, it is evident that the permittedbuilding area is generally used to the fullestextent. In particular, those plots lying at thefoot of the hill, with a maximum permittedbuilding area of 60%, demonstrate a remar-kably high sealing degree.

Where building density is higher, as e.g. inthe terraced house estates, there were pro-blems regarding use of ground, which affec-ted the planning of the soakaways. Garden

areas of the terraced houses are generallyunder the 50 m2 mark.

Here, the tendency was more towards un-derground soakaways, to enable the unbuiltareas to be used in other ways. Owners havein some cases subsequently covered overthe gullies, in order to enlarge the gardens,which are really quite small.

Diagram 3

Sealed areas (average values)

Terraced house – garden area

Terraced house – garden area

unsealed areas90974 m2

(44 %) saeled areas116479 m2

(56 %)

roof areas65181 m2

(31 %)

paths,parking spaces

51298 m2

(25 %)


The average proportion of sealed area con-nected to the public rainwater drainage viaa soakaway is shown in diagram 4. Drainageof the sealed areas not having direct connec-tion to the drainage system is assured enti-rely by seepage e.g. by rainwater beingchannelled to adjoining planted areas, orthrough choice of permeable surface mate-rial.

Diagram 5 gives distribution of the sealedareas, split according to above- or below-ground soakaway or retention system.Above-ground systems are gullies, soakawaybasins and the ponds; below-ground sy-stems are the trenches and retention chan-nels.

It will be seen that the larger part of thesealed surface is connected to an above-ground system. This is an important pointespecially relating to pre-purification of therainwater. The connected roof areas run intothe two systems in about equal proportions.

When channelling rainwater into an under-ground system, it wasconsidered importantthat an alternative pre-purification stageshould be available. Settlement shafts wereinstalled here, with and without floatingvalves, gravel filters and rainpipe valves withcleaning filters, among others. Furthermore,yard-drains and channels in carriageway are-as are to be installed as “Hanover model”i.e. with mud-trap and submerged valve.

The relationship between permeable andimpermeable sealed areas can be seen indiagram 6.

On average, 61% of the surfaces have beenlaid as permeable surfaces, including a largepart of the footpaths. For parking areas andaccesses, stone setts have mainly beenused. Permeable surfaces such as porousplaster, water-holding surfaces, wood panel-ling, honeycomb brick and gravel-basedgrassed areas are also to be found on theplots.

The building plan also prescribes roof plan-ting in certain areas of the project (see pa-ragraph 1, outline conditions). In addition,

Diagram 4

Diagram 5

Connection to the public drainage system

Distribution of connections

sealed surfacesnot connected

(100% soakaway)11 %

(23008 m2)

sealed surfacesconnected

45 %(93471 m2)

connectedroof areas

30 %(62126 m2)

connectedpaths,

parking spaces15 %

(31345 m2)

open water areasincluded in calculations

(part of the soakaway system)1 %

(1389 m2)

planted areas43 %

(89583 m2)

Areas in m2

Above-ground systems (100 % =̂ 49682 m2)

Below-ground systems (100 % =̂ 43789 m2)

0 10000 20000 30000 40000 50000

11430 (26 %) 32359 (74 %)

19915 (40 %) 29767 (60 %)

Pathways, parking spaces etc. Roof area


on some plots, roof planting has been plan-ned and carried out, although not requiredby the building plan.

An overall view of the proportion of roofplanting, and the number of systems whichhave been planted can be seen in diagram 7.Here, it must be remembered that the greenroof proportion on the individual plots doesvary between 2% and 100%.

Operation of the systems so far completedhas been as far as we are aware perfect. OnJuly 13th last year, on the Kronsberg therewas registered, within barely an hour, 36mm of rain. Statistically speaking, this isvirtually a one-hundred year maximum rain-fall. By comparison, from 01.07.1999 to13.07.1999 inclusive, total rainfall was 40.2mm. Average annual rainfall for the city ofHanover is 625 mm.Since all systems were designed and builtaccording to the rules of technology, andthus not for such a generous helping of rain,in theory, the systems should have over-loaded. In fact, of the 16 systems then inoperation, all functioned perfectly.

Not much can be said at this time regardingresidents’ acceptance of the soakaways.There have been discussions over possibleregular water levels in some soakaways, anddesign of the slopes from the point of viewof a possible danger of drowning for smallchildren. One of the systems was subse-quently redesigned, which means raising thefloor level to meet with general approval.

Diagram 7

Proportions of roof planting

Diagram 6

Permeable / impermeable sealed surfaces

Gravel gulley

Number of systems

The alterations have, however, yet to bemade.

As part of the water economy measures,economy taps were specified for the buil-dings. The use of rainwater in place of drin-king water was only accomplished in a fewcases. Some of the rainwater in these pro-perties then flows into the main drains sy-

stem. If this technology had been installedeverywhere, due to the competition with thesoakaway in respect of the water balance,the daily usage of rainwater would have hadto be restricted to 1 L/m2 roof floor area(Planning Team Water, 1995). Investors of-ten preferred the soakaway system, giventhese framework conditions.

total systems

planted

not planted

24

14

10

0 5 10 15 20 25 30

roof areasplanted

18830 m2

(29%)

roof areasnot planted46351 m2

(71%)

Impermeablesealed surfaces e.g.entrances, pathways,

terracing,limited numberpermeable of

accesses:20106 m2

(39 %)

Sealed surfaces e.g.parking spaces,

accesses,pathways:31192 m2

(61 %)


The many and varied building and artisticpossibilities for the soakaways can best beappreciated by a visit to the various plots onthe Kronsberg project. Four projects are de-scribed here, all of which include some spe-cial features. After that, a small selection ofprojects is shown in words and pictures,

In contrast to most other creative artworks,where rain is primarily presented as an opti-cal element to the resident or visitor, herein the North Park, the emphasis is on acou-stics, whereby the flowing rainwater is in-tended to create a “hearing experience”.

The surface of this Quarter’s Park is madeup of the central green area, and stone flagsenclosing it, between the wide, green-planted gaps of which the rainwater soaksthrough below ground level.

Rain-water running off the surface is takenup by strips of greenery, with gravel andchippings underlay, distributed throughoutthe park and by a box-channel which runsthe length of the park’s western boundary.The rainwater seeps through the strip ofgreen directly into the trench. The box chan-nel drains via ground outlets. In both cases,

Brief descriptions of some individual projects

simply to give an idea of what different sy-stems have been installed on the Kronsberg,and to whet the appetite for a look round.

The systems presented were chosen purelyat random, and were not subject to any sortof qualitative evaluation.

To make things easier, all the systems showncan be found on the map attached.

We cannot show all the systems, on all theother plots, for shortage of space, but theyare all well worth a visit.

North Quarter Park (water – an objet d`art)

the rainwater makes its way from there di-rect into the main trench.From here, the rainwater is led via a check-ing and maintenance shaft at a controlledrate to one of four “sounding shafts”. When

it drips onto a lower-lying water surface, thedripping rainwater produces a sound whichthe relatively larger sounding shaft magni-fies, and it can be heard through the soundopenings.

Box channel with sound opening

Quarter Park – general view

Rainwater shaft with sound opening

DN 150 outflow

common pipe with connectionto sluice shaft

sluice opening DN 21

runoff to trench DN 150

sleeve valve

DN 150

DN 100 overflow to next trench

checking- andmaintenance shaftwith control sluice

shaft withsound opening

channel

Cross-section

The energy-efficient development onthe Kronsberg is something veryspecial, because it represents acomprehensive environmental con-cept. The standard to which the en-ergy-saving houses were built In theKronsberg project was enhanced toinclude e.g. further improved heatinginsulation. On top of this, electricitywill be generated by a solar generator

and energy-saving domestic appliances willbe installed. Naturally enough, the rainwaterdrainage system is part of the concept. Drai-nage is via a gulley-and-trench system wi-th soakaway and controlled outfall. A specialfeature of the drainage is the roof-planting,which actually covers the entire roof area.


Along with the primary school, the Commu-nity Centre here also has a rainwater systemwhich can be used for saving water. Rainwa-ter is used for flushing toilets and urinals.

The rainwater used for flushing the sanitaryinstallations comes from the extensively-planted and gravel-laid roof surfaces via afilter into an underground water tank. Only

On this plot some 11.6 hectares (about 29acres), there are two identical rows of 8houses. The individual houses have a com-mon basement and are joined as well by anoverall glazed roof, creating a “micro-climate” zone.

It serves as a roofed-over, planted inner court-yard, and has a variety of pools and differentfountains. Some of the balconies and terracesare also within the zone.

Example for a comprehensive environmental concept (N13/14)

Terraced houses with roof planting

Soakaway gulley

Social and cultural community centre (drinking water ecenomy measures)

overflow water from the tank and the filterare allowed to soak away or are fed elsew-here.

The soakaway is a combination of trenchand retention channel. Most of the rainwaterwhich falls is stored and either soaks awayor flows away under control. A water basininitially envisaged was not included for rea-

sons of expense. Rainwater originating fromporous surfaces all goes to the soakaway.The vortex valve used to control rainwateroutfall has no moving parts and is, apartfrom a diaphragm used as a sluice, almostmaintenance-free.

Example of an inner courtyard dominated by water (M 52)

The open space between the rows of housesis to be devoted to an orchard, a play-areaand a lake area. Additionally, the houses areto have extensive and intensive roof-planting.

Rainwater falling on sealed areas will firstbe gathered in one of two tanks. The tanksare so sized that they will retain a proportionof the rainwater and an additional 35 m3

(some 7,500 gls.) for the micro-climate zone(including ponds etc.) and the greenery.

As the tanks are not designed to retain allthe required volume, when it rains heavily,rainwater will flow from the tanks into theponds and be stored there temporarily bythe increase in the water level of the pond.Drainage from the ponds is into a grassedgulley, under which there is a trench. A fol-lowing sluice then controls the rainwater’sflow into the public retention basins. Morewater retention capacity could be createdby using the play-area between lake andgulley-and-trench system.

Micro-climate zone

View of inner

courtyard


In building plot N 42, a pond takes up most of

the rainwater which falls. The rainwater is all

channelled into underground pipes. Some per-

meable areas allow the rainwater to soak direct,

or via planted areas, into the ground.

The Children’s day-care centre Kita 1 is drained by a gulley-and-

trench system. Interior fall-pipes lead the rainwater from the gra-

velled roof into the gulley, from where it soaks into the trench below.

The sealed pathways are also connected to the gulley. The few

parking spaces are permeably-laid, so that water soaks away on

the spot.

Nor

th E

nd


Three basins lined with gravel and bark slopes take most of the

rainfall on plot N43. To protect the sluice, the outfall is via a coarse

gravel filter. The remaining rainwater soaks away either where it

falls or in the adjoining planted areas.

Plot N22 is characterised by a wide-spreading and,

on account of the steeply-sloping nature of the area,

stepped trench system. Two shingle basins, known

as “wadis” take up water. Most of the completely-

planted roof surfaces, and parts of the road- and

pathways have direct access to the trenches.

Rain falling on the remaining roofs passes via the two

basins to the trenches Rain falling on other surfaces

either soaks away on the spot or via planted areas

and strips.

Rain drainage from plot N21 is via a soakaway

with drainpipes. Rainfall runs into the soakaway

almost exclusively over paved gutters and a gras-

sed gulley. To cross lower-lying parking spaces,

pipes cross them, aqueduct-style, at about 2.5 m

above ground, and empty into the paved guttering.

Rainwater on the parking spaces soaks away,

then runs to a pumping-shaft and from there to

the soakaway.

Pathways drain primarily into the greenery; roof

terraces drain via fall-pipes into small gravel

beds.


Rainfall on plot M21 soaks away through a basin with trench

below. Rainwater runs via open, tiled, guttering to a central

soakaway and from there into the groundwater or into the

basin. Rainfall on permeable sealed surfaces soaks straight

into the ground.

From some of the roofs, rainwater is channelled onto the roof

of the underground garage and used there for storage irrigation.

Excess water is fed via an overflow to the basin.

Rainwater falling on plot M42 soaks away through

a pond and a trench system.

Part of the rainwater is directed straight into the

trench via fall-pipes. The remainder reappears

after a few days, and is then fed, above ground,

to the pond through a system of gravel beds.

Some permeable surfaces are drained direct into

the groundwater by soakaways.

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On plot M 53, rainfall from most of the surfaces, and especially the roofs,

goes into a trench system comprising several parts. The remaining surfaces,

mostly roofs, are either connected to a soakaway basin or drain direct or

via adjoining planted areas.

The soakaway basin has an overflow through which, in torrential rain, excess

water flows straight to the trench system.

Plot M 41 has a combination of pond, trench and

gulley-and-trench. Rainwater is led visibly through

gravel or grass gullies to the pond or either direct

or over a soakaway via mainly open-ended fall-

pipes.

Underground garage roofs drain visibly through

gargoyles, also through box-drains and gravel

beds into the pond. Smaller sealed areas drain

direct into the greenery.

The primary school’s drainage system comprises a number of gullies with a filter pond and a trench

below. Rainwater from most of the planted roofs runs into a tank, to be used, and only overflow rainfall

runs into the filter pond. All other surfaces drain either direct into the pond or via a metal box-drain, then

round the school in gullies, and finally into the

soakaway. At the end of each of the gullies

there is a step, whereby the desired amount

of water can be retained. Most of the rainwater

flows above ground to the filter. The pipes

which are laid below ground come to the

surface in the middle of the greenery.


Minimum cost:Specific building costsof the sector cheapest to build

Average cost:Average of specificbuilding costs for all sectors

Maximum cost:Specific building costsof the most expensive sector to build

On the Kronsberg, due to EXPO, the buildingcosts for the gulley-and-trench system tur-ned out to be some 300.- DM/m higher thanoriginally budgeted. By contrast, the“normal” drainage costs for the years 1995-1997 on the Kronsberg were within budget.

Taking this competitive element into consi-deration, the scientific cost comparison nowlooks like this:

Gulley-and-trench system as installed byHanover:22,686,000.- DM

compared with a conventionaldrainage system:24,656,000.- DM

With introduction of the split charges forsoiled water and rainwater in 2001, the privateplot owners will also get considerable benefitin their drainage charges: assuming agree-ment of the Hanover city council, these char-ges may be reduced to 30% where rainwatermanagement systems are in operation.

Coststy of living, and must be so assessed. Withthe help of a cost-benefit analysis, it couldbe shown that decentralised rainwater ma-nagement, both in financial i.e. cost termsand – especially – in ecological and social,financially non-quantifiable terms, had anadvantage over conventional drainage sy-stems.

In the final report on the research project,costs associated with the rainwater mana-gement project amounted to20,384,000.- DM

compared to conventional drainage at24,656,000.- DM

This cost advantage arises mainly fromcounting rainwater management measuresas set-offs and replacement measures, asper nature preservation laws. Use of thegulley-and-trench system meant savings forthe city of Hanover of some 6,300,000.-DM.These costs would have been matched bythe costs of purchase of ground for compen-sation measures and its planting, if conven-tional rainwater drainage systems had beenlaid.

Economic situation after eva-luation of results of the muni-cipal competition

The following table displays the costs ofinstallation of the whole system, i.e. includingsite set-up, equipment and maintenancecosts, excavation work, pipe-laying etc.

In total, Hanover Municipal Water Authorityhad some 7,000 m of gulley-and-trench sy-stem laid, in about 20 sections. The costsgiven are for the end costs (nett) for eachsection, divided by the trench length, in DMper metre; they are thus costs of installationwhich were attained within the frameworkof the open competition.

Based on the market situation, and the va-rying extent of the individual measures, thecosts cover quite a wide range.

Decentralised rainwater management sy-stems are only a proposition, when compa-red with conventional drainage systems, ifthe economics are right. This is why in 1997Hanover Municipal Water Authority commis-sioned the Hydrological Institute at HanoverUniversity to compare a theoretical conven-tional rainwater drainage system for theKronsberg building project with the “closeto nature” concept actually realised there,from an economic viewpoint.

(1)

The economic evaluations were carried outwith the help of suitable process parameters.Factors studied were economics

a) from the point of view of the community, for the public drainage system,b) rom the point of view of the individual plot-owner, andc) from the point of view of overall

community economics.

From the community viewpoint, ignoringany ecological benefits, a straightforwardcost comparison favoured the decentralisedmanagement system. Based only on the in-vestment costs, it shows a cost advantagecompared with the traditional drainage sy-stem of about 17%. Specific costs of invest-ment for the area examined amount, withthe decentralised management system, toabout 61.- DM/m2 sealed surface.

From the viewpoint of individual plotowners, the conventional solution is themore favourable, as Kronsberg building costswould have been some 25% less than theywere with the decentralised managementsystem installed. The private builders andinvestors can all confirm this cost relati-onship.

Costs for the two systems would only beequalised once rainwater disposal chargesunder the decentralised management sy-stem were reduced to 60%.

From an overall economic point of view,ecological and social aspects must be consi-dered, as water management measures suchas these are designed to contribute to quali-

(1)Final report of the research and development project “Rainwater Management Hanover Kronsberg (Flood Precautions)”. Full-surfacerainwater management in a large-scale building project, with particular emphasis on flood protection aspects; sponsored by the FederalMinistry of Transport, Building and Housing and the Federal Ministry of Housing and Land (BBR); passed by the Hanover Municipal WaterAuthority to the Hydrological Institute of Hanover University for processing.Direction: Prof. Dr. Friedhelm Sieker; Management: Certificated Engineer Hans-Otto Weusthoff.

Total costs of the gulley-and-trench system

in DM/m trench

Manufacturing costs for theGulley-and-Trench system

Minimum cost 850,00 DM/m

Average cost 970,00 DM/m

Maximum cost 1150,00 DM/m

Economic and feasibility study


Bernd Altevers

Dr. Christiane Groß

Horst Menze

Kathrin Brandt

Anke Pieper

Frank Schulze

Ina Heeren

Ralf Kirchhoff

formArt, Hanover

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