AN INTRODUCTION TO THE EUROPEAN HYDROLOGICAL SYSTEM - SYSTEME HYDROLOGIQUE EUROPEEN, SHE .1. HISTORY AND PHILOSOPHY OF A PHYSICALLY-BASED, DISTRIBUTED MODELING SYSTEM
During 1977a nd1 978;
a ttentionw asc oncentrateodn the individuapl rocess componentosf the SHE. Snowmelti;
n terceptioann d evapotranspiratiwone re the responsibilityo f the Instituteo f Hydrology;
o verlanda nd channel flow dealtw ith by SOGREAH;
and the unsaturateadn ds aturatezdo necomponents were developebdy the Danish HydraulicI nstitute.E ach componenwt as con-structeda s a separatseo ftwarem odulew itht entativbe utw ell-defineidn formation exchangech aracteristicis.e;
certaini nformationg eneratebdy one module was to act as input data or boundaryc onditionsfo r otherm odulesA. t the samet ime;
a centralc ontrole lementt;
h eFRAME;
was designeda ndt estedb y the Danish HydraulicI nstitute;
f irst with dummym odulesa nd subsequently with workingm odulesa st heyb ecamea vailableT. he FRAME is responsiblfeo r the parallelr unningof the other componentsw;
h ichmay have differentt ime-steps;
a nd for the exchangeo f informationb etweenth em. By 1978i t becamep ossibleto construcat test systemfo r the SHE;
this being a corhpletes ystemb ut one which had beenp rogrammepdr imarilyf or testing purposes.T his version constitutedw hat;
in engineeringte rms;
is usually describeads a testm ule;
a lthoughin this caset heuse of the term mulew as equally well justified by the system'ss tubbornn atureand propensityfo r deliveringu nexpectedki cks to its developersD! ata from the Institute of Hydrology'sR iver Wye researchc atchmenitn Wales;
were used for general testing.H oweveri;
n dividualc omponentwse realso testedu singother sources of data (e.g. Jensen;
1981).T he Mule further servedt o demonstratteh e prac-ticabilityo f the softwares ystema rchitecturaen d it exhibitedc omputational performancceh aracteristic(es .g.r unnings peedst)h atwere well within those laid down earlier as being necessarfyo r its practicala pplication. Each of the ASHE organizationws orkedw ith its own versiono f the Mule;
keepinga ll componentfsix ede xceptt he one or two on which it was currently working.A t variouss tagesth eMule was updatedw iththe latestv ersionso f all the componentasn d developmenstt arteda freshw ith thesei ncorporatedA.t eachs uchu pdatingit was possibleto changeth ei nformatione xchangceh arac-teristicsa s necessaryD. esigna ndd evelopmenwto rk proceedeadt each of the three ASHE organizationsse paratelyb ut;
at each updatingo f the Mule;
a combinedw orkings essionw asheld in which engineeras nds cientistfsr omall three organizationpsa rticipated. The prototypeo f the SHE emergedfr om this processd uring1 981a nd was then subjectedto a more rigorous testing.T his showedu p a basic design weaknessin the systema rchitecturew hich prompteda n extensivere structuring of the FRAME;
togethewr iththe input and outputp roceduresT.h e SHE thus becameo perationailn its first productionv ersioni n 1982;
a lthoughf ur-ther extensivtee stinga ndd evelopmenwte rec ontinuedin ordert o increaseit s reliabilityr;
unnings peeda ndg enerael fficiencyF. rom1 983o nwardsth eASHE organizationsw ere joined in the testing programmeb y the University of Braunschweigs;
u pportedb y the GermanS cienceF oundationa;
nd;
from;
1984;
onwardsb;
y the Departmenotf Public Works of New ZealandA. collaborative venturefo r developintgh eSHE for irrigations tudiesw asset up with the Royal IrrigationD epartmenint Thailandi n 1985.A lso in 1985;
B ritishresponsibility for the SHE was transferredfr om the Instituteo f Hydrologyt o the Water ResourceS ystemsR esearchU nit at the Universityo f Newcastleu ponTyne;
wheref urthert estinga ndd evelopmenist b eingc arriedo ut.The Unit is funded by the U.K. Natural EnvironmenRt esearchC ouncil;