- 10. • 41 41 • • • • • • • • • • • • • • • • • • • • • • • •
I
• 0 • o • • • •
• • • go 0 RU FFORD PA RK FL OO D ST UDY : • a hy dro log ica l asse ssment
Report to Elliott and Bro wn Consu lt ing Enginee rs and Browne Jacobso n So lic itor s
Dr Duncan W Re ed • Institute o f Hy dro logy , Wallin g ford , OX IO 8B8 0 Fe b ru ary 1990 • • • • • 0 41
41 CONT ENT S 41 41 • INT RO DU CT ION 1 .1 Context • 1 .2 Sta tus o f re port 1 .3 Scope o f study • 1 .4 Gene ra l appro ac h 1 .5 Hyd ra u lic asp ec ts • 1 .6 W hy th e intere st in flood ra r ity ? 1 .7 F lood pro tection d esign sta nd ards • 1 .8 Struc tu re o f rep ort
• 2 CATCHM ENT CHA RA CT ER IST IC S
• 2 .1 Ca tchm ents o f inte re st 2 .2 Stand a rd chara cte r istic s • 2 .3 Ad justm en t o f M 5-2D va lu es 2 .4 Geolo gy • 2 .5 Hydro geology 2 .6 So ils • 2 .7 La nd u se • 2 .8 Cav eat 3 RA R ITY OF 22 APR IL 1983 ST ORM 41 3 .1 Gene ral cond itio ns 41 3 .2 Daily ra ingauge data 3 .3 Reco rd ing ra ingau ge data • 3 .4 Rad ar data 3 .5 Est im ate of catc hm ent ra in fa ll 41 3 .6 A sse ssm ent o f ra rity o f flood -p roducing ra in fa ll
4 RARIT Y OF 1 JUNE 1983 STO RM S
4 .1 G enera l co nd it io ns 4 .2 D a ily ra ingauge data 4 .3 Reco rd ing raingauge data 4 .4 Radar data 4 .5 Estim ate o f catchm ent ra in fa ll 4 .6 Asse ssm ent o f rarity o f flood-produc ing ra in fa lls
5 DES IGN FLO OD EST IMA TES
5 .1 Intro duction 5 .2 The statistic al ap pro ach 5 .3 The ra infall-runoff app roach 5 .4 Com paris on o f estimate s
6 SIMULAT ED RE SPON SE TO 22 A PRIL 198 3 STORM
• 6 .1 M eth od 6 .2 D ata 6 .3 F lood ra rity - RL ca tc hm ent 6 .4 F lo od ra rity - GHD and RW catchm en ts • S IM U LA T ED RE SPO N SE TO 1 JU N E 1983 STO RM S
7 .1 C a lc u la t io ns 7 .2 F lood rar ity 7 .3 A c heck
8 SUMMA RY AN D A DD IT IO NA L REMA RKS
RE FERENC ES
A P PEND IX 1 F lood Stu d ie s Re po rt nomenc la tu re
A P PEND IX 2 A greed ra in fa l l v a lu es
A P PEND IX 3 Ra in fa ll ra r ity a s se ssmen ts
A PPEND IX 4 C omp u ter list ing s o f hyd ro g raph s im u la t io ns 1 INT RO DU CT ION
1 .1 Context
A d am ag ing flood in c id ent occu rr ed at May lod ge Drive , Ru fford Park in Notting hamsh ire on 1/2 June 19 83 whic h bec am e the sub ject o f a leg a l d ispute betwee n a gro up o f pro per ty insure rs , Nott ingh amshire Cou nty Counc il and Brit ish Coa l . Notting hamshir e County Counc il m anage la nd and a reservoir imm ed ia tely dow nst re am of the flood ed site . Brit ish Coal car ry out deep m in ing in the ar ea w h ich le ad s • to subsidence . 41 The Institute o f Hyd ro logy (IH ) was approac he d by Ell io tt & Brow n Consult ing Eng in eers on beha lf o f the p ro perty • insu rers ' so licitor , B row ne Jacob son . In it ia lly , IH w as asked only to assess the ra rity o f the flood -p rod uc ing 410 rain fa ll . This led to tw o short stud ie s in 1988 . Fo llow ing legal dev e lopm ent s in the case , Elliott & Brow n app ro ac hed IH for furth er ad v ic e on 31 Octob er 1989 . A com p rehensiv e hyd rolo gic al asse ssm ent beg an in m id -Nov ember . 41 .2 ta t s o re o rt 41 This repor t pre sents the pr e lim inary results o f the ma in • stu dy . The ana ly sis su persed es that presented in tw o ear lier IH rep orts to E llio tt & Brow n . The conc lu s ion s are bro ad ly • in line with the first report (Stew art , 1988a ) . How ev er , in the se co nd re po rt (Stewart , 1988b ) an asse ssmen t was m ad e o f • the ra rity o f the comb in atio n o f sto rm d epth and antec ed ent 0 wetn ess exp er ienced on 1 Ju ne 1983 , base d on the assumptio n • o f ind ep endence and w ithout re ferenc e to a ra in fa ll -runo ff mode l o f flood re sp onse . That sh ortcu t to flood rar ity • assessmen t ha s sh ort com ings and has not b een fo llowed in the pre sent study . 41 1. co e f stud
411/ T he study has tw o ob je ctiv es . The primary ob je c tive is to 41 asse ss th e rar it ie s of the flo od ru no ff ev ents tha t occu rred fo llow ing storm s o n 22 April and 1 June 19 83 . The second ary 41 ob ject ive is op en -ended ; this is to com ment on hydro logica l asp ec ts of th e d ispute . 41 1 .4 n ra l a ro ach
Ass ess in g the rarit y o f a giv en floo d peak pose s a • statist ical p rob lem sim ilar to , but not id entica l to , th at o f a ssessing- the m agnit ude o f a flood o f a given rarity . • Several te ch n iqu e s are applicab le to either prob lem if exte nsive riv er flow and rain fa ll data are ava ila ble at , o r • nea r to , th e sub ject sit e . H ow ev er , wher e no fo rma l flow d ata are av ailable , it is ne cess ary to estimate the flood • po ten tia l by refe renc e to th e phy sical charact er istic s o f the catc hm en t . St andard meth ods are av aila b le to do this • (NERC , 1975 ; In stit ute o f Hyd rolo gy , 1985 ) bu t are known to • be inherently unc erta in . Consequently it is re comm ended that • re ference is a lso m ad e to su ch add it io na l info rm a tio n as can • • be fou nd (Inst it ute o f Hyd ro lo gy , 1983 ; Reed , 1987 ). T he add itio na l in fo rm atio n ca n take many fo rm s . More deta iled so il m aps and h is to r ica l flo od in form a tion are tw o exam p le s o f ad d it io na l data tha t may be re levant .
1 . d ra u lic as ec s
Loca l fea tu res o f a dra inage sy stem w ill in fluenc e the way in w h ic h a g iv en flo od ru no ff event le ad s to inundatio n and dam age to pro perty . The re la tio nship betw een flow ra tes and wate r leve ls is larg ely a matte r o f s ite cond it io ns and hy d ra u lics ; re levan t facto rs w ill be the d es ign and ma in tenance o f channels , cu lv erts , br idge wate rw ay s and em bankm ents , and als o the des ig n , ma in te na nc e and op eratio n o f var ia b le cont rol dev ices , such as s lu ice ga te s . In th is in sta nce it appears tha t d i ffe rentia l su bsidenc e due to m in in g may have bee n an important facto r a ffec ting th e riv er flow at w hic h unw an ted inund at io n beg ins and th e sev erity and extent o f su bsequent dam age to property .
T he se hyd ra u lic co ns ideratio ns are la rgely outw ith th e p re sent stu dy . Re ferenc e to la nd lev e ls is only m ad e to esta b lis h the possib le sign ific anc e o f gro undw ater contr ib utio ns to the flood ing in cidents at May lodge Dr iv e . It is for others to det erm ine the effe ct tha t su bsid ence may hav e had on d im in ish ing the le vel o f pro te ct ion again st inu nd at io n prov ided by th e var ious em b ankm en ts at Ru ffo rd Park .
W the tere st in ood ar t
H ere the concern is to assess the rar ity o f th e pe ak flo od runo ff from the catc hm ent . If the hy d ro lo gic al asse ssm ent ind ic a tes that floo d ru no ff on 1/2 June 1983 was exc ep t io na lly rare , th ere m ig ht be ground to arg ue that some d e ee o f a a e was inev it ab le , th at a particu lar flo od pro te c tio n stru ctu re was no t designed to w it hsta nd su ch an extre m e event , and /o r th at su ch an occurrenc e cou ld not reaso nab ly ha ve bee n exp ec ted . On the other hand , if the asse ism ent show s th at th e peak flow on 1/2 June 1983 was not exc ep t io nally rare , suc h argum ent s m ay be found wantin g .
W hile the rar ity o f the pe ak flood ru no ff may we ll be relev ant to the ca se , the qua lifica tio n "som e degre e of damage " m ay a ls o be impor tant . Even i f the hy dro log ic a l cond it io ns g iv in g r ise to the flood ing on 1/2 June 19 83 w ere show n to be exceptio na lly rare , the actio ns or inactio ns o f the De fendants may nev erth e le ss have stro ngly in fluenced the exte nt- o f flo od ing e xp er ie nced , and the exte nt o f conse quent ia l d am ag e to pro perty . • • .7 Fl ec e s a
Such a rgum ents w ill depend pa rtly on w hat is deem ed to be • except iona lly ra re . This 'is a lso outw it h the hy dro logy . How ev e r , it is no ted that nom ina l desig ns stand ard s adop ted • in land drainage design on m a in r iv ers are ty p ically in the 30 to 50-y ear ev ent ra nge fo r ru ra l areas and the 50 to 150- 40 yea r ev en t ra nge for urban areas . The Sev ern -T re nt Re g io n o f th e Na t iona l Rivers Autho rity m ig ht be a source o f more • spec ific gu idance ; however , neit he r th e Rainworth Water nor the Ga llow Ho le Dyke is an adopted "ma in riv er " . It is • believed th at any respons ib ility fo r prescrib ing drain age sta nd ard s at Ru fford Park there fore re sts w it h the New ark • and Sherw ood Dis tric t Counc il .
• It m ay be re levant to d istin gu ish dra inage "lev e ls o f se rv ice " ex pected genera lly fr om tho se e xpec ted when II spec ific works have be en unde rtaken to reduce the frequency o f flo od in g . It m ight be ar gued that , through m in ing AD su bs id ence , Brit ish Coa l hav e /imp osed an additiona l flood r isk . It is w e ll known (eg . Royal So cie ty , 19 83 ) th at • judgem ents o f acc eptable risk are strong ly in fluenced by wheth er exposu re to th e haza ra is cho sen or im posed . • 1 . t ctu e o f o t • St udy catc hm ents are de fined and their characte ristics • re v iewed (Sec tion 2 ). T he flood -p roduc in g storm s are co nsid ered in Sectio ns 3 and 4 an d ra rit y as se ssm ents m ade . • St andard proced ure s for est im at ing des ig n. floods are app lied 0 in Sectio n 5 to prov ide a yard stic k against whic h to m easure • the rar ity o f the 22 Apr il 19 83 and 1/2 June 1983 floods , whic h a re s imu late d in Sectio n s 6 and 7 . Fina lly , • conc lus io ns are summarized in Sect ion 8 , and a rem ind er g ive n that the hy drolog ic al a ssessm en t p rovid es only one • inpu t to re solv in g w hy the dam agin g flo ods occurred .
• o
• • • 2 CATCHM ENT CHARACT ER IST IC S
2 . nte
In m any flood assessm ents it is su ffic ient to consider only one catc hm ent , ie . all land that dra in s to the su b ject site . How ever , th e c ircumstances at Ru fford Pa rk a re unu sua l and it is ad v isab le to cons ider sev era l ca tchm e nts . T he im portant one s are illu strated in Fig . 2 .1 , whic h is an ag reed p lan .
Fir st , it is appropria te to cons ider the Ra inworth Wa te r catchm ent to Ru fford Park . T h is is de fined here as th e to pograp hic catchm ent o f the Rainwor th Wate r to its con fluence w ith the Ga llow Ho le Dyke . The c atc hm ent , coded RW , exte nd s from Cox Moor (near Kirby in A sh fie ld ) in the so uthw eRt to Ru fford Park in th e northea st , w it h an are a o f 59 .0 km 4 . At first sig h t th is appear s to b e th e only area re levant to flood ing at May lodge Driv e . How ever , bec ause o f the prox im ity o f May lodge D riv e to the Ra inw or th Water/G a llow Ho le Dy ke con flu ence , it is ap pro pr iate to consid er a lso the com b ined Ra inworth Wate r and Ga llow Hole Dy ke catchm ent to th eir con fluence Rt. Ru ffo rd Park , re ferred to as the RW +G HD ca tchm ent (74 .2 km' ).
Fo r spec ia l re asons d is cu ssed b elow , it is als o relev ant to consid er the Ga llow H ole Dy ke (GHD ) catchm e nt a lo ne .
Because o f the prese nce o f an im poun d ing r e serv o ir (Ru fford Lake ) ju st down stre am o f the Ra inwor th Wat er con fluence w ith th e Ga llow Ho le Dyke , it is re levant to co nsid er the ent ire catc hm en t dra in in g to tha t sit e also . Flood assessments the re may be re levant to those interpret in g th e hydra u lic per form anc e o f the d is cha rge control struc ture s at Ru fford Lake . Th is catchm eRt is re fe rred to as th e Ruffo rd Lake (RL ) catc hm ent (75 .7 km 4 ) .
Fin a lly , for com p leteness , th at part o f the Ra inwort h Water catchm ent that d ra ins through t he "L " La ke ab -R a inworth tow n has a lso d is tin gu ished . T h is is re ferred t o as the Upper Ra inwort h Wate r (URW ) catchm ent .
• t ard c te st s
Sta nd ard characteris tic s (NERC , 1975 ) of t hese five catchm ents are g iven in Tab le 2 .1. T he Flo o d S tu d ies Rep ort (FSR ) nom enc la tu re is d efin ed in Append ix 1 .
Va lu es o f stream freq uency , ST MFRQ , w ere d e riv ed from 1st Serie s 1 :25000 m aps (as recom me nded in th e FSR ). The urb an fract ions (URBAN ) were der iv ed by re fe renc e to a 1:50000 map pub li shed in 19 87 . Neit her the exten t nor ra te o f urb an ization o f any o f the five catc hm ents is su ffic ient to make the flood rarity assessm ents signific a ntly dep end ent on the d ate o f surv ey . A lt ho ugh 36 % of the RW catchm ent dra ins through the "L " La ke a t Ra inw orth , the lak e area is to o sm a ll to qu a lify as a sig nific ant la ke acc ord in g to th e FSR sta nd ard . •
41 AD Comment is w arr anted on the v a lues show n for M 5-2D , wh ich have be en ad justed by d irec t analy sis o f loca l ra in fall • data . • 2 . d t en M -2D v es • M5- 2D d2no te s the 2-d ay rain fa ll depth o f 5-y ear retu rn per io d . A valu e o f M 5-2D ra in fa ll is norm ally read by • supe rimposin g the ca tchm ent bound ary draw n at 1 :62500 0 sca le on to a st an dard m ap g iven in Vo lum e V o f the FSR . How ev er , • long -term research at IH on ra in fa ll frequency estimation has d em onstrate d tha t som e rain fa ll stat is tics g iv en in the • FSR are over-genera lize d (eg . Da le s and Reed , 19 89 ). Est im ates of M 5- 2D we re the re fore verif ied by d irect • ana ly sis o f d aily ra in fa ll record s for gauge s in or nea r the RL catchment . The se gauges are show n in Fig . 2 .2 . M 5-2D • values were deriv ed as the geometric mean of t he uppe r half o f annua l maxim um 2-d ay rain fa ll depths , ie . by the method 41 u sed in Vo lume II o f the FSR . The d irec t ana ly sis che cks for any lo ca l error in the M 5-2D m ap and ex p lo its, t he longer per iod s o f re cord now ava ilab le . 41 From F ig . 2 .2 it is seen that the st an dard map und er est ima te s th e M 5-2 D rain fa ll sta tis t ic . T he catc hm ent • va lues adop ted for M 5-2 D are tho se sh ow n in Tab le 2 .1 . 41 Re tu rn pe riod s qu ote d in th is re port are tho se • mea sured on the annu al maxim um scale , in which 41 ret urn period represe nts th e av erag e in terva l rathe r • tha n be tw een all exc eed anc es . Where return period s on th e "p eak s ov er thr eshold " scale 41 are requ ir ed , these are te rm ed mean recurrence in te rv als be tw een exceedan ces . 41
•
•
• • • Fig . 2 .2 Map and gauged valu es of M 5-2D ra in fall sta tis tic
[numb ers in pare nt heses denote numb er o f years o f record use d in ca lcu latio n o f gau ged valu es ]
43 50 40 . 40
50
52-81271 RL C atchm ent 0 62-7(2 3 1 SI • 55 5 (671 56-51231
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50 66-6 1231 • ...... As - --. 33 4 3 . 50 • 2 .4 Geo logy 41 In the sta nd ard FSR flood est im atio n methods , the solid and 41 d rift ge o log ies hav e an in flu ence only in so much as th ey a ffec t the W inte r Rain fa ll A ccepta nce Po tent ia l (W RA P ) 41 c lass ificatio n (see Append ix 1). How ev er , pa rt ly beca use of the lim ite d sp atia l reso lut io n o f the 1 :625000 WRAP map , it 41 is re lev ant to exam ine more d eta iled maps whe re th ese a re ava ilable . The ca tc hm ents lie on one -inch "so lid and dri ft" 41 maps no s . 112 and 113 .
41 T he d om in ant geo logy on the RW catchm ent is Bunter — Sand sto ne , now ge nera lly term ed Sherwood Sand stone . On the eastern marg in s o f the catchm ent the G re en Be ds and Ke up er Wate rsto nes ap pea r . Drift deposits are not exte nsiv e , be ing 41 lim ited to sma ll patc he s o f G lac ia l Sa nd s & G ravels , Bou lder C lay and Head . • In contra st , m ost o f the GH D ca tchm ent lies on the Keu per 4111 W ate rstones an d Green Bed s . Some super ficial c lays are marke d , part ic ularly in the w est o f the catchm ent . 40 In th e RW ca tc hm en t , alluvium is lim ited to the main cou rse • o f th e Ra inwor th Wate r . In the GHD catc hm ent , a lluv ia l deposit s a re shown on both the no rthern and south ern • branc hes o f th e Ga llow Hole Dyke . • 2 . d o eo o
• The she rw ood Sand stone is a m a jor aqu ife r of regio nal 0 imp or tance . Ex te nsive abstrac tions for p ub lic wate r su pp ly • ar e mad e at sites w ithin an d c lose to the topograph ic ca tchm e nt . The se ab st ra ct ions hav e a st ro ng loc al in fluence • on gro und water leve ls . In most ca ses , because the rate s o f ab str ac tio n ar e re lativ e ly un iform , a characteristic sp at ial • pro fi le o f gro undwate r leve ls is m ainta ined . T he aqu ife r re spond s re latively slow ly to e ffective rainfa ll , the ma in per iod o f rechar ge gene rally be ing in la te w inter and sp r ing (January to April ). 41 A 1 :100000 hy droge o logic al m ap is availab le (Inst itute o f • Ge o logic a l Science s , 198 1) and sh ow s app ro xima te groundw ater contours derived from b ore ho le data for M arch 19 78 . Be li eved 41 to be ty p ica l, this sna psh ot confirm s that th e grou ndwater catc hm ent is marke d ly d ifferent from th e topograp h ic 41 catchm en t . A t times whe n the Ra inwo rt h Water is in hy dra u lic cont inu ity w ith the aqu ifer , the contib uting ground wate r • catc hm en t exte nd s pr inc ip ally to, the west . Wh ile it is alway s le ss extensiv e than the topographic ca tchm ent , th e • v aria ble na tu re o f the groundw ate r ca tchm ent is one fa ctor w h ich accounts for the unusu a l flow reg imes o f th e Ra inworth 41 W ate r . In particular , at tim es o f h ig h gro undw ate r lev els , le vels in the Sherw ood Sand stone aq u ifer undou b ted ly • in fluence gro undwate r levels a t May lod ge Drive . 1111 N eighbou r ing river s in the reg ion , su ch as the Po u lter , M eden , Maun , (and th e Trent ) , hav e th eir headw ate rs on less • p erm eable geology . Where these oth e r riv ers pa ss ov er the
• • Sherw ood Sa nd sto ne outcro p , they are generally held to be in fluent (in fluent t o the aqu ife r ), w ith som e river wate r passing to the aquife r . How ev e r , above its co n fluence w it h the Ga llow Ho le Dy ke , the Ra inworth W ater catc hm en t lies a lm ost exclu siv e ly o n the h ig hly pe rm eab le She rw ood Sand sto ne .
In these c ir cum stanc es it is likely that m uch o f th e flow in the Rainworth Wa ter is co nt rib u ted by ripar ian area s clo se to the wate rc ourse . T here appears to be no ev id ence to su ggest th at the ur banized area at the he ad o f the catc hm en t is we ll connected to the riv er sy stem . How ev er , it appea rs like ly that urb an areas c lo se to the Rainw orth Wate r (ie . at Ra inworth and in th e we stern fr inges o f B ils th orp e ) w il l contrib u te s ig ni fica nt ly to the flood response o f the RW catc hm ent . Ana lo gou s ly , w hile there appea rs to be no ev id ence tha t d raina ge from C lip stone Fore st is well conne cted to the riv er sy stem , it ap pear s like ly that m in era l extra ct io n act iv itie s m ay co ntribu te som e water s . There is som e ev idence for th is in the typ ic al b lackness o f the r iv er wate r .
A comb inatio n o f fac to rs su ggests th at flow s in th e Rainw orth W ater are partly su pported by groundwate r . The 1st Se r ie s 1 :25000 m ap show s a numb er o f sp rin gs c lo se to Ru ffo rd Park . Ey e-w itness ev id e nce o f the June 1/2 19 83 flo od in g in c id ent re fe rs to the dif ficult ies that the Fir e Au thority had in pum p in g th e M ay lodge Driv e re sid enc es and gard ens dry (Statement o f M rs Sto rer ). This again su gg ests that "natu ra l" g roundwate r d is charges in t he area contr ibute se aso nally to Ra inwo rth Water flows w hen reg io nal ground wate r leve ls a re high . Long -term wel l record s , for exam p le at Bils thorpe , ind ic ate that groundwater leve ls w ere hig her in 19 82 and 1983 than they had bee n since 1977 .
V ery little o f the Sherw ood Sandstone ou tc rops in the Gallow Ho le Dyke catchm ent . T here the aquife r is confin ed by the much le ss perm eable Green Bed s and Keu pe r W ate rsto mes . Howev er , th e cone of depre ss io n , produced by ,ground wate r abstra ct ion for pub lic wate r su pply c lose to Ompto n , pro bab ly le ads to so m e reduct io ns in low flows in the ad ja cent course o f the Ga llow H ole Dyke . A check rev ea led that reg iona l and tem pora l patterns o f gro undwater ab stract ion in 19 83 w ere no t unusual . 2 .6 soils
The 1 :62 5000 W RAP map bro ad ly d istingu ishes the generally very perm eab le so ils asso cia ted w ith the Sherw ood Sand sto ne o f the Rainworth Wa ter catc hm ent from the m uch le ss perm eab le so ils over ly ing the G reen Bed s a nd Keupe r Waterstones o f the G HD ca tc hm ent . Ad d it iona l deta il is now pro v id ed by u niv ersa l 1 :250 000 so il maps (So il Su rv ey o f Eng la nd and Wa le s , 1983 ). T he ir inte rpre ta tion in terms o f W in ter Rain fa ll Accep ta nc e Potential requ ires skill , stand ard cate gorizat io ns not y et be in g av a ilab le . How ev er they are u sefu l to th e hy dro lo g ist becau se th ey prov id e greate r sp atia l deta il . This is not too in form ative for the 41 41 59 .0 km 2 RW catc hm ent wh ich is show n to be dom inated by two 41 so il assoc iat ions : the Cuckney and Delamere , N th o f them highly perm eab le . How ev er , the sm a ller 15 .2 km ' Gallow Hole 41 Dy ke catc hm e nt has more contrastin g so ils , th e Hod net asso cia tion bein g rath er more perm eab le than the su rface • wate r g leys o f the Bro ckhurst associatio ns .
• An altogeth er more det a iled m appin g o f so ils is prov id ed by 1 :25000 map s , whe re av ailab le . Fe w d is tr icts have bee n • map ped at th is sca le but th e 5K66 grid square "0 11e rt on " is on e o f them (Rob so n and George , 19 71). T he map and • asso c iated m ono grap h p rov ide excep t ionally deta iled in form ation abou t the so ils o f bo th the Gallow Hole Dy ke • catc hm ent and much o f the low er part o f the Ra inworth Water catchm ent . 41 In add it ion to the gre ate r d etail , two spec ific m ap p in gs from th e 1 :25000 map ,are of sp ecia l interest . F irst , the 411 1 :2500 00 so il map and maps d erived there from - such as the ID 1 :100000 ground water vu lner ab ility map (Soil Su rv ey and Land Re sea rch Centre , 19 87 ) - show a r ip ar ia n area imm ed iately • nor th o f B ils thorp e and east o f the Rainw orth W at er as posses sin g ty p ica l sta gno gley soils . This co nt rad ic ts th e • 1 :25000 map , w hich show s the same typ ica l br ow n sa nd s that ar e ch arac te r is tic o f much o f th e Rainwo rth Water catchm ent . • An enq u iry to the Soil Survey met the response th at the more deta iled 1 :25000 m ap is corre ct . • The se cond fe atu re o f note is tha t the 1 :25000 map cle arly • ind icates th at th e so ils at , and immed ia te ly up st re am o f , Ru fford Pa rk are o f the Comp to n serie s . The monog raph • (Rob so n and Georg e , 197 1) de fines the parent mate ria l to be "c layey alluv ium and hill-wash ma in ly fr om Keu per M arl or • Waters tone s " . This prov ides geom orp holog ical ev id en ce tha t , th e Ga llow H o le Dyke has been as in fluential as (or more • in fluentia l than ) the Rainw orth Water in the h is to r ica l • flood ing o f la nd a t Ru fford Pa rk . Both the na me "dyke " , and ID the prese nc e on the 1st Ser ie s 1 :25000 o f embankm en ts alo ng th e southe rn bank o f th e Gallow Ho le Dy ke add-w eight to the 41 su ggest ion th at , in it s natura l sta te , the Ru fford Pa rk area was as sensit iv e to inund at io n by flo od s from the Gallow • Hole Dyke catchm en t as from the Ra inwort h Wa te r catch ment . • 2 .7 Land use 41 H ISTO RY • A feel for the h is tory o f th e are a can be ga ined from W ild 's his toric al de sc rip tion o f the Rainw orth area (W ild , 19 72 ). • It is ap paren t th a t ma n has in fluenced flows in the Rainworth Water fr om at leas t the early 19 th Centu ry . A ro und 41 th e tim e o f W ate r lo o , a numbe r o f rese rv o irs w ere co ns tr ucted up st ream o f Rainworth to improve croppin g • th ro ug h irrig atio n . Som e o f th ese rese rv o irs rem ain . In the low er cou rse o f th e Rainwort h Water c lose to Ru fford Park , • th er e is som e ev id enc e tha t th e waterco ur se was d iverte d to pe rm it ir rig atio n o f the most fert ile flo od p la in land . U lt im ately , this d iv ersio n has served to p erm it deve lopm ent o f the flood p la in at Ru fford Pa rk fo r hou s ing .
The 20th Century ha s seen man 's in fluence in the incr ease d exp lo it at io n o f gro und water for pub lic wa ter su pp ly . T he re has been d isruption to drain ag e by m in ing , most notab ly w he re su bs idence ha s led to d ifferen tia l sett lem ent o f se ctio ns o f w aterco urse s and fis suring .
M IN ERAL EXTRA CT ION
Tw o m a jor co llie r ies lie in th e stud y are a : Bils th orpe Collie ry (m a in ly dra in ing to the Gallow Ho le Dyke catc hm ent ) and Ru ffo rd Co lliery , ad jacent to th e Ra in w orth Wate r . The quant it ie s o f w ate r abstra cted from grou ndw ate r for coal- washing and d is char ged to the Ga llow Hole Dyke and Ra inworth Water a re o f no d irect conseq uenc e to flood flow s . It is presu m ed th at any pumped d ra inage o f m inew ater is -likew is e in sig n ificant in te rm s o f flood flow s in t he re ce iving watercourse s .
A ma jo r Coal Stockin g S ite ap pears to ex tend ov er the natura l course o f the Rainworth Wat er . I am not aw are o f any suggest io n that this situat ion , or those o f var ious wastewater sett ling lagoo ns , had an appre c iable e ffec t on flood flow s in the Ra inworth W ater in the 19 83 event s . How ev er , giv en that new settling lagoons w ere p la nned at the tim e (D is charge Consent No . WQ /7/1889 , dated 14 Sep tember 19 82 ), it w ou ld be he lp fu l to hav e c on firm ation tha t no untow ard in c id ents occurr ed at the se s ites whic h m ight hav e led to a su dden increase in flow s in the Ra inworth Water in the 1/2 June 19 83 ev ent .
FO RESTRY
The Ra inw orth Water catchm ent lies in wha t was once a natu ra l dec id uous w ood la nd : Sh erw ood Fore st . A subst antia l part o f the catchm ent contin ue s this trad it ion w ith conifer p la ntatio ns at T hieves Wood and C lip stone Fore st (see F ig . 2 .3 ). G iv en the v er y perm eab le soils , this land use is not tho ught to aggrav at e flood ris k . (On le ss p ermeab le soils p re -a fforestatio n dra in ag e may g ive r ise to a tem po ra ry incre ase in flo od r isk .)
A ma jo r tourist att ractio n , the Sher w ood Forest Coun try Park is now sit ed in the C lip stone Fore st part o f the catc hm ent . How ev er , th is d ev elo pm ent post-d ate s the flo od in g incid ents und er i n v e s t i g a t i o n .
GRO UN DW ATER A BSTRA CT ION
T he re are a numb er o f m a jo r gro undwater pum ping sta tio ns in or close to the top ogra phic catc hment . The se ab stra ctio ns for pub lic w ater supp ly are sig n ific ant in som uch as they low er the natura l groundwater table fo r pro longed periods . How ev er , in Sp r in g 19 83 , gro und wate r leve ls in the Sherw ood Sandsto ne w ere a lready re la tiv ely hig h . T hus the part icu la r
10 •
El Ur b a n are a s
For • st
• L• ktis
M Mi ning
0 Groundwater a bstr act io n. f or pub lic w • t ei suppl y
0
12 _ .. .. _ 9 10km so• l• • = m1.
.11
• • • • • • • • • • • • • • • • • 0 0 • • • • • • • • • • • • • • • • abstrac t ions be in g m ade at the time o f the flood ing inc id ents are not thought to be of s ignific anc e .
A PEC UL IAR ITY
Dur ing the second ha l f o f the 1970s , the Ra inw orth Wate r cam e und er partic ula r scru tin y for its la c k o f wate r . Th is co in cid ed w it h a pe r iod w here reg iona l groundw ater leve ls in the Sherw ood Sandstone were dec linin g pe rs iste nt ly , prim arily in resp on se to low w in ter ra in fa ll bu t possib ly a ls o in respo nse to ov er-ab stractio n . Pa rt icu la r d ifficu lt ie s were , and to som e exte nt still are , exp erie nc ed in the pub lic wate r su pply ab stract io n at Ru fford Pumping Stat ion . Sit ed c lose to the Ra inwor th Wate r (see Fig . 2 .1), it was su sp ecte d tha t adv erse boreho le wa ter quality was re la ted to poor river wate r qua lity . Re searc h dem onstra ted (F inch , 19 79 ) that the presence of a very larg e fissu re ga ve rise to a lo ss o f riv er water to th e aqu i fe r , and to one production bore hole in partic u la r . O ne the ory for th e fis su r ing w as that , at th e tim e , it was cu stom ary in m inera l extra ct io n for a supporting p illar to be le ft und er pum ping stations ; w h ile this p ro te cted the pum p insta lla tion , d ifferentia l se ttlem ent may hav e led to fissu r in g .
The re levance o f th is to the fl ood behav iour o f the Ra inworth Wa ter is tha t sub sid ence due to m ineral ex tr ac tion may hav e in creased the te nd ency for the Ra inw orth Wate r to be in flu ent (to the aq u ife r ), partic u lar ly in its m iddle reach es . Coup led wit h the dec lin ing re gio nal groundwate r leve ls throughou t the 1970s , th is m ay hav e d is gu ised the flow reg im e o f the Rainworth Water a nd le d to a lack o f attentio n to , or und erest im atio n of , pote ntia l drainage prob lem s .
O TH ER
A ccord in g to MAFF record s stu d ied by Rob in so n (per s . com m ., 19 89 ), there w ere few gra nt -a id ed fi eld dr ainage sc hem es in the catchm ent in th e 19 70s . The heav ier so ils, o f th e Keuper Waterstones m ig ht be expe cted to hav e attr ac te d some works and the record s suggest that th is ha s been th e case to the south , in the parish o f Eakrin g . For adm in istrative reasons - partly re la te d to con fident ia lity - it is not po ss ib le to be spe cific about the locat io n and t im ing o f d rainage work s . It wou ld seem like ly that d ra in age improv ement s car ried out in the area are those ty p ic a lly used on the var ious so ils . Thus no spec ia l allow ance is w arran ted .
2 .8 Caveat
W hile the cha ra cter istic s o f the catchm en ts ha ve be en d is cusse d in considerab le d eta il , the in fo rma t ion cou ld be re fined by fu rther re fe re nce to the vario u s so urces .
The stand ard methods o f flo od e stim ation a pp lied in Section 5 take e xp lic it account on ly o f a lim ited nu mber o f catchm ent characte rist ics . In the case o f the W inte r 0 Ra in fa ll A ccepta nce Po tent ia l cla ssificat ion , the stand ard • method uses so ils in form at io n map ped at a very coarse sc a le .
41 Impro ved flood est imates co uld be ob ta in ed by ma king use of the add it io na l de ta iled in form at io n pre sented abo ve . 41 How ev er , th is wou ld re qu ire the exerc is ing of considera b le jud gement , w hich experts mig ht no t read ily ag ree on . 41 There wou ld hav e b een m ore to be gained by clo se scru tiny o f 41 th e catc hm ent ha d subsequ en t ana ly sis (Sectio ns 3 , 4 , 6 and 7 ) sh ow n th e flo od ev en ts to be very rare . It is well known 41 that the estimat io n o f very rare flood s on hig h ly permea b le ca tchm ents (such as th e RW catc hm ent ) is prob le matic ; it 41 m ight be argued that extrem e ev en ts on such catc hm en ts a re produced by in frequent comb inations of fa ctors - such as 41 he avy ra in fa ll in g while topsoils are fro zen . In such ca ses , th e norm a l flood be hav io ur m ay no t be a good gu id e to the •41 suprano rm al .
111 The req u irem ent fo r more de tailed ana ly sis be cam e largely acad em ic whe n it was con firm ed th at th e storm and flood • incid en ts were by no means exc ep tio na lly ra re , a nd it wa s learnt that this m ig ht be read ily agreed by the De fendants . 41 In prom oting such an agreem ent , there appe ared to be nothing to be gained by re fin in g flood es timat es in a non-standard 41 mann er . T hu s much o f the in form at io n gathered and sc rutin ized in the stu dy ha s not been u sed in the 41 asse ssm en ts o f ev ent ra rity tha t fo llow . 41 41 •
• 13 3 RA R IT Y OF 22 APR IL 19 83 ST O RM
Four sourc es o f in form a tion are d iscussed se pa rate ly be fore bein g bro ught togeth er in Sec tio n 3 .5 .
1 ener cond itio ns
Accord ing to the pro o f o f ev id enc e by Mr Mead ow s : "Du ring the ev enin g o f Friday 22 April 1983 th e area was sub jecte d to torrent ia l thunderst orm s " .
.2 Da ra i u e da t
An ag reed se t o f da ily ra in fa ll to ta ls is repro duced as Append ix 2 to this repo rt . T he value s are keyed to ra in ga uge lo cat ions show n on Fig . 2 .1 (appended ), which is also an agreed docum ent .
Rain fa ll tota ls record ed for the 24- ho ur period end ing at 09 .00 on 2 3 April 19 83 ra nged fr om 7 .8 mm at Su tton Sew ag e Works (gauge A ) to 35 .3 mm in west Farns field (gauge J ). The re levant ra in fa ll re ading s are g iven in Table 3 .1 .
TABLE 3 .1 Daily ra in fa ll read in gs - 22 April 198 3
Gauge depth Th iessen Gauge dep th Thie ssen (mm ) w eig ht (mm ) weig ht
A 7 .8 0 .03 I 21 .0 0 .135 C 14 .4 0 .15 J 35 .3 0 .0 1 D 16 .0 0 .12 L 16 .0e 0 .135 F 28 .2 0 .07 N 22 .2e 0 .05 G 20 .9e 0 .04 0 13 .0 0 .02 H 2 1 . e 0 .24
V alu es w it h su ffix "e " are estim ate s w hic h deriv e from ga ug e rea d ings m ad e le ss freq uently tha n d a ily . The se apportio nm ents w ere mad e by the Met . O ff ice in the no rm al course o f the ir qu ality contro l o f d a ily ra in fa ll data ; the y appear to be reasonab le .
The gauge read in gs suggest that th e ra in fa ll was somewhat m ore int ense in the Low er Ra inwort h W ate r and Ga llow Ho le Dyke catchm ents than in the U ppe r Ra inworth Wate r catchm ent . G au ge H a t Ru fford Pum p ing Stat ion is re la tively ce nt ra l to the comb in ed Rainworth Water and Gallow Ho le Dyke catchm ent s (RW +G HD ), and had an apportio ned depth o f 2 1 .8 mm .
d in u e data
Ra in record er char ts were exam in ed for Mans field Sewage W orks (gauge B ), Gle ad tho rp Expe rime nta l Husba nd ry Fa rm nea r Warso p (gauge M ), Markham C lin to n Pu mp ing Sta tio n (Me t . O ffice gauge no . 123376 , s it ed abou t 2km no rth o f gau ge K ) and Brac kenh urst (gauge P ). None o f the gauges is w it h in th e catc hm ent . • These data su ggest that the sto rm mov ed app ro xim ate ly So uthw est to Northeast acro ss th e are a , rain fa ll occu rr in g slight ly earlie r at Bra cke nhu rst and M ans fie ld th an at Gle ad thorp , and much earlier than at M a rkham C lin ton .
At Mansfie ld , a ll but 2 .5 mm o f the da ily to ta l o f 14 .6 mm fe ll betw een 17 .25 and 19 .40 hr GM T . Ra in fall w as inte nse 0 betw een 17 .30 and 17 .45 , slac ke ned be tw ee n 17 .45 and 18 .50 , then m od erate ly in tens e until 19 .40 . A t Gleadthorp , whic h re ce iv ed a daily to ta l o f 19 .8 mm , all bu t 2 .5 mm fell betw ee n 17 .45 and 19 .45 hr GMT , w ith the most inte nse ra in fa ll betw een 17 .45 and 18 .00 b ut m od erate ly in te nse ra in fa ll betw een 18 .55 and 19 .45 .
ada d ta
Weath er rad ar data are availa b le fo r th is da te from th e Ham e ld on H ill sta tio n in No rthw est Eng la nd . T he fo rm at o f data is hou rly read ings ov er grid squares of sid e 5 km . It is w ell know n th at rad ar da ta are use fu l in rep re senting w here and when it ra ins , but le ss good at de te rm in ing • intens it ie s . "Ad justm ent factors " applied by th e Met . O ffice can d iffe r by more than a fa ctor o f ten . Because th e stu dy • area is a lo ng way (ab ou t 10 0 km ) from the ra dar site , the quality o f ra in fa ll est imates der iv ed from radar d ata is • like ly to be further degraded .
• The radar data ind icate tha t heavy ra in fa ll on 22 April 198 3 was ma in ly co n fined to the per iod 17 .00 to 20 .00 hr GM T . The • data d em onstr ate that ra in fa ll wa s w idespread thr ougho ut a • 0 35 by 35 km area centred on C lips tone Fo rest . The tempora l • and sp at ia l reso lu tions o f the da ta are insu fficient to de fine th e mov em ent o f ind iv id ual sto rm cells w ith • con fid enc e . How ev er , the w id er fi e ld o f radar dat a is co nsis tent w ith a poss ib le genera l mov em ent from Southwest • to Nor theast . A nota b le fea tu re in the ra dar data is a North-S outh band o f hig her va lu es over Boughton , Eakr ing and Halam .
st a e o f c tc h e t in fa l
An e st im ate of the av erage ra infa ll ov er the 75 .7 km 2 catchm ent to Ru fford Lake was ob ta ined as a w e ighte d av erage o f 11 da ily gaug e read ings , ba sed o n th e method o f Thie ssen polygons . T he we ights are g iv en in Tab le 3 .1. T h is schem e y ie ld s a dep th o f 19 .1 mm fo r 22 A p ril 19 83 .
The corresp ondenc e betw een radar d a ta and gauge data is rath er poor . For this event the rad ar data und erest ima te IS dep ths appre c iably . In term s o f sp a tia l variatio n , the ra dar data ind ic ate tha t the gre atest dep th s w ere experie nced in a North -S outh a lignm en t ov er Boughto n , Ea kr ing a nd Ha lam ; the gauge d ata su ppor t this genera l alig nm ent but su gg est tha t the greatest d ep th s wer e exp er ie nc ed further w est , ov er Edw in stow e and west Fa rns fie ld . W itho ut a very deta iled 0 invest igat ion o f the ge neral chara cteris t ics o f Ham e ldon ra dar e stim ates fo r the study are a , it w ould appe ar
0
15 inadv isab le to p lace any g re at relia nce on the radar data for this sto rm .
Fro m the rec ord in g rain gauge data - g iv ing prom inence to th e G le ad tho rp gauge (wh ic h experie nced a daily depth sim ilar to the estim ate d catchm ent av erage ) - it is ju dged tha t 17 mm o f the 19 .1 mm fe ll in th e ma in storm pe rio d , and tha t , at th e catc hm ent centr o id , th is wou ld have la sted from 17 .30 to 19 .45 hr GMT .
The temporal d is tribution o f ra in fall seen at the re cord ing ra in gauges ind ic ate s that the most inten se ra in fa ll occ urred in the fir st 15 m inutes , fo llowed by inte rm itte nt intense ra in fa ll for th e ne xt 75 m in ute s , with mod e ra te ly in tense and fa ir ly un ifo rm ra in fa ll in the fin al 4 5 min ute s . A re presenta tio n o f the tem po ra l pro fi le is g iven in Tab le 3 .2 , for la te r u se in Sectio n 6 .
TA B LE 3 .2 Estim ated te mpora l profile for 22 Ap r il 1983 sto rm ind ex to % o f 30 -m inute st orm eriod th 1 30 Index 1 re fe rs to 2 10 17 .30 - 18 .00 hr GMT 3 15 4 30 5 5 ota
ssessm e o f rar it o f flood - oduc in ra i all
Fr om Sec tio n 3 .5 it is conc lu ded tha t the flood -p roduCing sto rm com pris ed a catc hm ent ra in fall o f 17 mm in 2 .25 hou rs . Usin g th e stand ard F lood Stud ie s Rep ort proced u re - but the pre ferred est imate o f t he M 5-2D stat is tic (see Se ctio n 2 .3) - this corre sp ond s to a 1 .8-y ear ra in fall ev en t on th e annua l m aximum scale . Put anoth er way , th e ann ua k exc eedance probab ility o f a 2 .25-h our catchmen t o f 17 mm o n the Ru fford La ke catchm ent is 0 .56 . For such a fre qu en t ev ent it is ap p ro pria te to conv ert the retu rn pe riod to th e "pea ks ov er thresho ld " scale . Applicatio n o f La ngbein 's form ula y ie ld s an estim ated mean in terv a l betw een e xc eeda nces o f 15 months for this 2 .25 hour catchm ent ra in fall dep th . Ca lcu lat io n deta ils are g iv en in Ap pe nd ix 3 .
Thu s the sto rm ev ent is judged to be unexc eptio nal .
(C. 0
• 4 RAR ITY OF 1 JUNE 198 3 STO RM S
The so urc es o f in form at io n ava ilab le fo r the 1 June 1983 • sto rm s are b ro ad ly as b e fore , and are d iscu ssed in turn . It sho uld be noted that on ly partia l rada r data are av ailab le 0 for this event .
• How ev er , the main d ifficulty faced in a ss igning a ra rity to th e floo d-p rod uc ing ra in fall is th at two separate sto rm s 0 occu rred on 1 Ju ne 1983 . Whethe r the tw o storm s were su ffic ient ly sep ara ted in t ime to re present tw o ind ep end ent 0 flood -p roduc ing events is dou bt fu l . Fo r this rea so n , th e catc hm ent ra in fa ll asse ssm ent tha t follow s is he lp fu l m ore 0 for later use in Sectio n 7 th an fo r assig ning simp le ra rit ie s (or a comp lex comb ined ra rity ) to th e 1 June 1983 • sto rm s .
T he sto rm s fe ll on the sam e day (1 Jun e 1983 ) but on AD separa te "ra in fa ll d ay s " : 31 May and 1 June 19 83 . AD ne ra in fo at ion
1ST STORM
T he first storm occurr ed in the ea rly hours o f 1 June 1983 . T he sta tem ent o f M r Be llamy ind ica te s that he avy rain fa ll commenc ed at 5 am and ceased at 9 am . Br it ish Su mm er T im e was in force and tim ings given by w itnesse s are th ere fore one hour la te r than GMT tim ings . • 2ND STORM • T he re ap pears at fir st s ight to be some con tr ad ict ion in • acc ou nts o f the t im ing o f the se co nd sto rm . S tatem ents ta ken from M r L ieber and M r Ketc hell on 9 Ju ne 1983 re fer to torrentia l ra in from 7 .15 pm until 8 pm ; Mr Ke tc he ll ad ds : "but no t to an exte nt o f being gre ate r than p rev ious exp er ienc es" . La ter st atement s by M r L ieber a nd Mr Be llam y (take n in Ju ly 19 87? ) say tha t th e ra in sto rm began at 6 pm and la sted until 7 pm . T he proo f o f ev id ence - b y Mr Mead ow s sta te s th at "Ab ou t 8 pm a furthe r down p our o f rain be gan " . A po ss ib le exp la nat io n for th ese d iffere nt perspectives is g iven in Sectio n 4 .3 .
e da
1ST STO RM
Rain fa ll totals (see Append ix 2 and Tab le 4 .1 ) re cord ed for the 24-hou r perio d end in g at 09 .00 on 1 June 1983 ranged from 25 .5 mm at Edw in stow e (gauge E ) and 26 .6 at Mansfie ld (gau ge 0 ) to 37 .1 mm at Sutton Sew age W orks (gau ge A ). The gaug e mos t centra l to the catchm ent (gauge H at Ru fford Pum p ing Statio n ) reg istered 28 .1 m m . The spat ia l un iform ity o f these read in gs would seem rem arkab le g iven th e lik ely -0 conv ective nature o f the storm th at th ese to ta ls la rgely rep re se nt .
17 Am ongst gauges not read on a regu la r ba sis , a h ighe r va lu e w as in fe rred by the Met . O ffice for Edwin stowe Wate r Reclamat io n W orks (122939 , 46 .1 mm ) . How ever , th is apportio nm ent was made in rou t ine qua lity cont ro l o f data w it hout re fe rence to the observat io ns at Edw in stowe (122928 ), wh ic h is the next nearest gaug e . The Met . O ffice ceased to u se data fr om Ed w in stowe in 1977 , presumab ly becau se read in gs were no t bein g taken su ffic ie ntly regu la rly .
Exam in atio n o f rain fa ll m ea su rem ents for the ent ire per iod 27 May to 2 June 1983 revea ls w hat appear to be an om a lies in the Ed w in sto we and Edw in stowe W RW read ing s . The 4-day read in g at Edw instow e for the 27-30 M ay sugg ests th a t heavy rain fa ll w as exper ie nc ed in th is per iod a s well as in the 31 May to 2 June period . Cross-r e fere nce to the Edw instow e WRW read ings suggests th at both sites experie nced he avy rain fa ll on 30 M ay 19 83 , over and abov e that exp er ienc ed at o th er sta tio ns in the stud y are a . Th is is not re flecte d in the M et . O ffic e apportio nm en t fo r Edw in stow e W RW and th e la tter is there fo re in doub t . A pre fe rred apport io nm ent is tha t 20 mm fe ll on 30 M ay and 36 .5 mm on 31 M ay , and this is assumed in su b sequent analys is .
2N D STORM
A n add it io na l w orry concerns the Ed w instowe WRW read ing for 1 June 19 83 . Two sou rc es , one the M et . O ffice com pu te rized data set , show 8 .3 mm bu t a Severn -T rent Wate r Aut hority source shows an unequ ivocal 28 .3 mm . The la tte r valu e has there fore been adop ted .
Rain fa ll tota ls for the 24 -h our per iod commenc i ng 09 .00 on 1 J une 1983 w ere generally sm alle r and more varia b le than for 31 M ay 19 83 . They ranged from 1.5 mm at Sutto n Sew age Works (gauge no . 122707 ) to 28 .0 mm in west Fa rn sfie ld (1 1873 1 ) and 28 .3 mm at Edwin stowe W RW (122 939 ). Th e Ru fford Pum p ing Statio n gauge registered 21 .0 mm .
T he relevant ra inga uge read in gs are g iven in Tab le 4 .2 .
Is 40 Rain re cord er ch art s were exam ined fo r gauge s at Mans fie ld Sewage W or ks (gau ge B ), G le adthorp (gau ge M ), M arkham • C lin ton (ab ou t 2 km north o f gauge K ) and Brackenhu rst (gauge P ). The re cor ds for B ra cke nhurs t w ere in co mp lete ID while the reco rd at G le adth o rp was a ffecte d by a pa rt ia l blo cka ge in th e ra ingauge on the first day . Because o f the • ab senc e o f rad ar d at a fo r t h is d ay , add it iona l re co rd ing ra in gauge data were exam ined for site s fu rther a fie ld , at • Watnall (Met . O ffice gauge no . 117626 ) and Torkse y Pump ing Stat ion (122084 ). • 1ST ST ORM • These data indic ate tha t , apart from neg lig ib le amounts • aro und 20 .00 hr GMT , the da ily to ta ls fo r 31 M ay 19 83 re present rain fa ll betw een about 03 .00 and 08 .00 hr GMT on 1 • Ju ne . It ap pear s that heavy rain fa ll at any one sit e la sted for 3 .5 to 4 ho urs , w ith ra in fa ll commenc ing e arlie r in the • southw est (eg . Watna ll ) and la ter in th e north east (eg . Mar kham Clinton and Torkse y ). A t all sites th e ra in fa ll was • genera lly heavy and cont inuous , but w ith particu lar ly inte nse burst s ev ident tow ards the begin n ing a nd end o f the 40 sto rm period .
2N D STO RM
• Reco rd in g raingau ge charts fo r the 1 Ju ne 1983 indica te that there were thre e perio ds of ra in fa ll : genera lly neg lig ib le • am ount s around 10 .00 hr GMT , and tw o intense p eriod s o f rain fall in the early evenin g , each last in g be tw een 20 and 40 35 m inut es , and sep arated by a 90 m inut e ra in less in te rm is sion . An exceptio n is the Bra ck enhurst gau ge w hich • ind icate s a much lo nger in te rm is sio n ; ho w ever , the cha rt reco rd the re is in com p le te . 40 Char t tim ings -are thought to be f air ly re liable for th e • M ans field Sew ag e W or k s and G le ad thorp re cords . T hes e ind icate tha t each burst comm enc ed synch ronous ly at both • sites , at abou t 16 .15 and 18 .10 hr GMT re spe ct iv ely . That the re were tw o bursts m ay account for th e appa rent con fu sion • in w itne sse s ' sta te ments (se e Section 4 .1 ). •
• .4 adar data
1ST ST ORM
No radar data were ava ilab le .
2N D ST ORM
Fo r this flo od in g in c id en t , rad ar da ta are av a ila ble only for the per io d from 17 .00 hr GMT on 1 Ju ne 1983 . The ir tempora l pattern ag rees w e ll w ith the reco rd ing rain gauge data . The radar data in dic ate that there w as cons iderab le spat ia l v ar ia b ility in th e ra in fall experie nced in the ev en ing o f 1 June . Intere st in g ly the heav ie st ra in fa ll dep ic te d by rad ar is again or ie nted in a North -S outh d ir ectio n ov er Bo ug hton , Eakr in g and Ha lam , whereas gauge data aga in su ggest that the heav iest falls were further west , over Edw in stow e W RW and w est Farns field .
4 . t im ate o ca tchm ent ra in fa
The Thiesse n w eig hting procedu re was used to obtain an estim ate o f catchm ent av erage ra infa ll ov er the 75 .7 km ' catchm ent to Ru fford Lake . The Thiessen we ights (Tab le s 4 .1 and 4 .2 ) d iffe r slightly fr om those used in Se ct io n 3 .4 because ra in fa ll re ad in gs w ere available from gauge E for these storm s .
T he proced ure y ie lded dep ths o f 29 .4 and 14 .1 mm re sp ect iv e ly for th e 24-hour pe riod s end in g and beg in n ing at 09 .00 GMT on 1 June 19 83 .
1ST STORM
From the record ing rain gau ge da ta it is judged that 29 .2 mm o f the 29 .4 mm fe ll in th e m ain storm pe rio d , and that , at the catchm ent centr o id , th is wou ld hav e la sted from 03 .30 to 07 .30 hr GMT on 1 Ju ne 1983 . W e ight was giv en to th e d at a record ed at Mans fie ld and M arkh am C linton .
T here is ev id ence that th is sto rm pa ssed from Southwest to Northeast , a ffecting the G allow Ho le Dy ke catc hm ent a lit tle la ter than the Ra inw orth W ater catchm ent .
2N D STO RM
From th e record ing ra in gau ge d a ta it is judged tha t 7 .7 mm o f the 14 .1 mm da ily tota l fo r 1 Ju ne 1983 fell be tw een 16 .15 and 16 .45 hr GM T and 6 .1 mm fe ll betw ee n 18 .15 and 19 .00 hr GMT . The la tter a ssessment tallie s w it h th e conte mpo rary statements o f M essrs . L iebe r and Ketc he ll . Ev idence fo r s ignific ant storm movem ent associated w ith th ese bursts o f rain fa ll is w ea k .
Approx im ate tem po ra l pro fi le s fo r th e ca tc hm ent av erage ra in fa ll in these storm s a re g iv en in Tab le 4 .3 .
t o TAB LE 4 .3 Estim ated tempo ra l pro files for sto rm s on 1 Ju ne 19 83
1ST STO RM 2ND STO RM
t ta •
Index 1 re fe rs to Index 1 re fers to 03 .30 -0 4 .00 hr GMT 16 .00 - 16 .30 hr GMT
4 . sse ssm e t o f t o flo od - ro ucin ra
The first st orm in cludes a period in w h ich 2 8 .0 mm fe ll in 3 .5 hours . Su ch a catc hm en t av erage fa ll has an asse sse d ra rity o f 5 .33 years on the annu a l max im um sca le , corre spo nd in g to a mea n .rec urre nce in terv al of 5 8 mon ths .
T he seco nd storm d id not re pre se nt a no table fa ll in it self A ca tchm ent av era ge fall o f 13 .8 mm ha s a retu rn per iod o f 1 .20 years on th e annu a l max imum sca le . This correspo nd s to a mean recurre nc e in te rv al o f 7 m onths .
The tw o storm s to gethe r y ie lded a ca tchm ent av erage fa ll o f 43 .3 mm in 15 .5 hou rs , corresp ond ing to a 5 .79-y ear event for this durat ion . The equiv a lent mea n recurre nce interv al is 63 months .
The Calcu lation deta ils are give n in Appendli 3 .
2.I 5 DES IGN FLO O D EST IMAT ES
.1 I oduc on 411 As d iscusse d in Sectio n 1 .4 , standard methods are av ailab le (NERC , 19 75 ; In stitute o f Hyd ro logy , 1985 ) to estimate flood pote nt ia l by re fe rence to phy s ic al cha racteris tic s o f the catchm ent . App licat io n o f the se stand a rd m ethod s is cons idered first , fo r the "stat istic a l " ap proach (Se ction 5 .2 ) and the "ra in fa ll- ru no ff " approac h (Sect io n 5 .3 ). T he 411 estimates are compa red in Sec t io n 5 .4 .
The sta t stica l a ro a h 40 Estim ates o f the T-y ear peak flow are ob ta in ed by first estim at in g an "index " flood and then app ly ing regional fl000d "grow th facto rs " .
The Flo od Stud ie s Report (NERC , 1975 ) use s th e m ea n annua l flood , Q BA R , as the index flood . It is de fin ed as th e II ar it hm et ic mean o f annua l m ax im um in stantaneou s flow s . typ ic a lly it has a return per io d , on the annua l maximum II scale , o f ab out 2 .33 y ears . T he sta nd a rd equat io n for estim at ing QBA R on "u ngau ged " catchm e nts is : II
QBA R = c AREA ' 94 STM FR()'27 SO IL 1 '23 R SMD 1 °3 (1+L AK E )- '95 II where c=0 .02 13 for the Centra l Regio n (wh ic h inc ludes the 40 Trent basin ). Th ig W es an estimate o f the mean annu al flo od , Q BA R , in m 4s- s ; se e Se ct ion 2 .2 and App end ix 1 for ID de fin it io n o f the other term s .
Estim ates o f Q BA R are g iven in Table 5 .1 fo r the various catchm ents consid er ed in th is study .
A desig n flo od o f low er fr eq uency (and th ere fore hig he r retu rn per iod ) is est im at ed by mult ip ly ing QBA R by an appropria te growt h fa c to r . This fac to r is used to "scale up " 40 the mean annu a l flo od (QBA R ) to the T -y ea r flood (Op ). For exam p le , the Sev ern -T rent regio na l flood g rowth fac for fo r 40 the 50-y ear retu rn per iod even t is : 40 OT / Q BA R = 2 .20 .
T hese estim ates suggest that th e sm a l l (15 .2 km2 ), but re la tive ly im per meab le , G a llow Hole Dy ke qatc hm ent p re se nts a h ig her flo od pote nt ia l tha n t he 59 .0 km Ra inworth Wa te r catchm ent to the ir jo in t conflu ence near M ay lod ge Drive .
40
40 411 fl 40 • • TABLE 5 .1 F lood estima tes - "sta tis tica l" ap proach • (all figures are in m 3s - 1) URW RW GHD RW +G HD RL • 21 .3 km 2 59 .0 km 4 15 .2 km 2 74 .2 km ' 75 .7 km 2
• QBA R 0 .96 3 .18 3 .95 6 .27 6 .35
• Q 2 0 .86 2 .83 3 .52 5 .58 5 .65 0 5 1.18 3 .91 4 .86 7 .72 7 .81 • 0 10 1 .43 4 .73 5 .89 9 .35 9 .46 Q 20 1.7 1 5 .65 7 .03 11 .15 11.29 • Q 30 1.88 6 .22 7 .74 12 .28 12 .43 0 50 2 .11 6 .99 8 .70 13 .80 13 .97 • 10 2 .47 .17 10 .1 16 .12 1 .32
Bec ause th e est im a tion o f de sign floods from phys ical cha racte rist ics is inhe rent ly error pro ne , it is inadv isab le to rely on estimates by a s in g le method . In ad d ition to pro v id in g altern at iv e e stim ates o f pe ak flow s , the ra in fa ll- runo ff m et hod ca n pro vid e a representa tio n o f th e flood hydrog ra ph . This is o f part ic u lar intere st in th is case to che ck that the Ra inworth Wa ter and Gallow Ho le Dy ke catc hm ents are broad ly sens itive to the same k in d o f flood- produc in g st orm s , desp it e the ir d iv er se physic a l cha racteris tic s .
Summ ary re su lts fr om app licatio n o f th e FSR ra in fall-ru no ff met hod , as mod ified in F lood Stud ie s Su pp lem entary Re port • No . 16 , are given in Tab le 5 .2 . D is the des ig n sto rm duration and 0BA SE deno te s the ba se flow a llowance . The • stand ard method- su ggests that the catc hm ents w ill be gen era lly se nsit iv e to pro lo ng ed periods o f ra in fall o f many hou rs .
That th e Gallow H o le Dyke catchm ent is represented as be ing no mor e quick ly re spo nd ing than the Rainw orth W ate r catchm ent Is slig ht ly surp ris ing . It is exp la in ed by a comb ination o f fa ctors . First ly , a ltho ugh the GHD cat chm ent has steeper ov er la nd slo pe s , the av era ge slope o f its ma in ch annel is s ignific antly less tha n tha t o f the RW catchm ent . Se cond ly , the GHD c atc hm ent is alm ost entirely ru ra l whe rea s the RW catc hm en t has a significan t urba n fract io n . Fin ally , the GHD catc hm en t has a slightly lower average a nn ual ra in fall th an th e RW ca tc hm ent . T hese character is tic s ($ 10 85 , URBAN and SA AR ) a ll appea r in the es tim ation equation for the chara c te ris t ic response time , Tp (0 ), and hen ce in fluenc e the des ig n sto rm dura tio n , D .
0.3 •
.4 om ar so of e st imates
A greem ent betw een the sta tist ic a l and ra in fall -runo ff est im ates is generally go od fo r the GHD catchm ent , w ith th e ra in fa ll-ru no ff approa ch giv in g on ly slightly la rger estim ates . H ow ever , for the oth er ca tchments consid ered , the est im ates by th e ra in fa ll -r uno ff ap proach are m uch la rg er than those by the statis tic a l approach .
W hether the sta nd ar d me th od s provide an adeq ua te repre se ntatio n o f the catc hm ents is doub tfu l . In th e ra in fa ll-ru no ff met hod , the est imat ion eq uatio n for Tp (0 ) • does not rep resent the like ly scenar io that ru no ff contrib ut io ns from non-rip ar ia n par ts o f the catchm ent overly in g th e Sherwood sa nd sto ne will travel bo th more slow ly and ov er greate r d is tances than th ose fr om rip arian areas sit ed on alluv ium or le ss permeab le soils deriv ed from hillw ash . In contra st , in the sta tis t ical ap pr oach , the stream frequency te rm , STM FRQ , prov id es som e ...repre sentatio n o f the slo wer respo nse exp ec ted from the Sherw ood sand st one • areas . • It is in stru ct iv e to compare the flo od est imate s for the URW and RW catchm ents . V isual in sp ection o f the st ream channe l • at Ra inw orth fo llow ing heav y ra in fa ll , con firmed in d is cu ssio n w it h a lo ng -te rm lo ca l re sid ent , ind ic at es that • the flood potentia l o f the U pper Ra in worth Wat e r is very m od est ; ru no ff is he av ily contro lled by na tu ra l gro undwater • sto rage and - to a lesser extent - by ro ut ing t hrou gh the "L " Lake . In contrast , v isua l inspec t io n o f th e lower • Ra inw orth Water (eg . at th e Ma nor Fa rm cu lvert immed ia te ly upstream o f Ru fford Park ) in d ic ates a much more app rec iab le • resp onse . The statis tic al ap proach (typ ica l ra t io : RW = 3 .3 URW ) rep re se nts the d ifferent respon se characte r istic s o f • the URW and RW catchm ents m ore realis tica lly than does the ra in fa ll-r u no ff meth od (typ ic a l ratio : RW = 2 .0 URW ). • • • • • 0
• A fu rt he r unsa t is facto ry feature o f th e flood estimate s by 411 th e ra in fa ll-runo ff metho d is that tho se for the comb in ed Rainwor th Wate r and Ga llow Ho le Dy ke c atc hmen t exceed the 41 sum o f the corre sp ond in g flood est imates for the ind iv ivdua l ca tchments . This is illo g ica l . G iv en the diverse na tu re o f 411 the cat chm ents , it se em s un like ly that they w ill be se ns it iv e to precisely the same flood -p roduc ing cond it io ns . 41 In such circum sta nc es one w ou ld there fo re exp ect th e des ign floods for the comb ined catc hm ent to be somew hat less than 411 the sum o f the ind iv id ua l de s ign flood s .
• • • •
• •
• • • • • 1_5 6 S IMULATED RESPO NSE TO 22 APR IL 198 3 STORM
6 .1 Method
Flo od Stud ie s Supp lem enta ry Report No . 12 (Inst itute o f Hydro lo gy , 19 83 ) se ts out a m eth od fo r as sessin g the re tu rn per iod o f a nota b le flo od us ing the ra in fa l l-ru no ff ap proach . The method is su it ab le whe re amp le ra in fa ll data are ava ilab le .
There are tw o im porta nt prin c ip les . F irstly , the ra rity o f a g iv en ra in fa ll occur rence (eg . 30 mm in 4 hou rs ) is no t necessa rily a good gu id e to the rar ity o f the resu ltant flood . T his is becau se a g iven catchm e nt m ay no t be in tune w it h the part icu la r c ha ra cter o f the extrem e ra in fa ll . For exam p le , flo od in g in heav ily urb anized ca tc hm ents is generally sens it ive to sho rt-d uration high -in te nsity ra in fa ll whereas flood ing in la rge (u sua lly s low ly- resp ond in g ) riv er ba s in s genera lly ar ise s from prolonged and w id esp read heav y ra in fa ll . A lso , the sever ity o f th e re su lt in g flood m ay b e in flu enced by o ther factors such as th e d ry ness (or w etness ) o f the catc hm en t p rior to the main sto rm . U se o f a rain fa ll-runo ff method can a llow for this .
The second gu id in g pr in cip le o f the F SSR 12 method is tha t th e sam e ra in fa ll-runo ff m od e l is used to s imu la te the notab le flood as is u se d in ca lculating des ig n flood estim ates . The merit o f th is is that the re w ill be some te nd ency for errors to cance l out . Fo r exa m p le , if the ra in fa ll-runo ff m ethod ov ere st im ates the v o lume o f runo ff resp onse (eg . through m isc la ss ificat io n o f the W inter Ra in fa ll Accepta nce Pote nt ia l o f the soils ), th is ca lib ration erro r w ill in fla te bo th the de s ign flood estim ates and the sim u la te d nota ble flo od . Thus the asse ssm ent o f flood rarity is le ss sensit iv e to err or than is the flood peak es t im ate it se lf.
6 .2 Data
An esiim ate o f antecedent catc hm ent w etn ess is obta in ed from ro ut ine m ap ped v a lues o f Soil Moistu re De ficit (SMD ) and ca lc u la ted v a lu es of the 5-d ay Antec eden t Precip itatio n Index (AP IS ) using the st and ard defin it ion :
CW I = 12 5 - SMD + A PIS w he re CW I denote s Catchm ent W etne ss In dex . The d aily rain fa ll read in gs at Ru ffo rd Pumping Sta tion (gauge H ) were used in the ca lc u latio n o f A P IS . Est im ates o f SMD w ere ta ken by re ference to rou tine m apped value s prov id ed by the MORECS serv ic e op erated by the M et . O ffice .
The ca lcu la tio n for the 22 Apr il 198 3 storm is summar ized in Tab le 6 .1 . • • • TAB LE 6 .1 An tec eden t catchm en t w etness - 22 A pril 1983 Tim e SMD AP IS CW I • (GMT ) rem mm mm
41 09 .00 0 .0 6 .6 131 .6 .1 13 1 .1 sa 1 1 41
• . AL catch e t
• Using the storm dep th o f 17 .0 mm derived in Sect ion 3 .5 , the tem po ral pro fi le g iv en in Table 3 .2 , and the CW I va lue from • Tab le 6 .1 , the simu lated hyd ro graph for thq 2 Ap ril 1983 flood to Ru fford Lake had a peak o f 8 .54 m 's - s (see Appendix • 4 ). Com par ison w it h the des ig n flood estim ates g iven in Tab le 5 .2 y ie ld s an assessm ent o f a 2 .55-y ear flood on the 41 ann ual max imum scale , corresp ond in g to a mean recurre nce interva l o f 24 months . This is no t very d ifferent from th e es t imat e o f rain fa ll rarity as a 2 .33-year st orm .
• HD a d RW c tc hmen s
• Ra in fall was ra ther heav ier ov er the GHD catchm ent (20 mm ) than the RW catc hm ent (16 mm ). Sepa rate hy drog ra ph • simu latio ns a re in cluded in Append ix 4 . T hese sugge st tha t , in term s o f flood ru no ff at Ru fford Pa rk , the RW and GHD • catchm ents contr ib uted sim ilar quantitie s o f flow in this • ev ent . • • • • • • • • •
• • • • • 7 S IMULA T ED RESPO NSE TO 1 JUN E 1983 STORM S
7 . a lc at o
Anteced ent catchm en t wetne ss is summ ar ized in Tab le 7 .1 .
TA B LE 7 .1 An te cedent catc hm en t wetn ess 3 1 May 11 Ju ne 1983
Date Tim e SM D A P IS CW I (GMT ) mm mm mm
3 1 May 09 .00 0 .0 4 .5 129 .5 1 June 03 .30 0 .0 2 .8 127 .8 (say 128 ) 1 u 1 . 2 . 14 . sa 14
Becau se o f the d istinct ante ced ent we tne ss co nd it ions , it is necessa ry to sim u late the flood resp onse to th e seco nd storm se parate ly from that to th e first sto rm ; these are giv en in Append ix 4 .
Sim u la tio ns fo r the tw o sto rm s have been comb ined in F ig . 7 .1 to ind ic ate the com b in ed respo ns e o f the Ga llow Ho le Dyke and Rainworth Wate r to Ru fford Park , taking acc ount o f both sto rm s . T he simu la tio ns suggest that the second sto rm led to a "shou lder " on the hy d ro graph recession from the m ain p eak .
7 .2 F ood rar t
The com b in ed hydro gr ap h has an estimated peak o f 12 .7 m 3 s- 1 occurr in g at abo ut 14 .00 hr GMT on 1 June , ie . abo ut tw o hours pr io r to commenc ement o f the second sto rm . U sing th e RW +G HD desig n flood est im ates g iven in Tab le 5 .2 , this comb in ed pea k flow is asse ssed to be a 5 .4-y ea r event on th e annua l maxim um sc ale , corr espond ing to a mean recurrence in terv a l o f 59 month s .
Thu s , fo r th is ev en t , the flo od pe ak rarity is asse sse d to be very s im ila r to that o f the flood -p roduc ing ra in fa ll (see Sectio n 4 .6 ).
7 .3 A c heck
For rea so ns d isc ussed earlie r (see Sections 2 .4 to 2 .7 and Sectio n 5 .4 ) the re is dou bt that the rain fa ll -runo ff method prov id es a fa ith ful re presentatio n o f the flood resp onSe o f the v ery perm eab le Ra inworth Water ca tc hm ent , particu la r in terms o f it s re la tiv e tim in g to tha t o f th e Gallow Ho le Dyke .
A t an ear ly stage o f the stu dy a se arc h was mad e for a nearb y gauged catc hm ent w ith sim ilar cha ra cte ristics . Wh ile th ere are so me geolo gic al and so ils d ifferenc es , the m ost near ly analogous ca tchm ent w ith form a l flow record s is judged to be the Gre et at Southw ell (gaugin g station no . 28072 ). • • Fig . 7 .1 S imu la ted hydrogr aph for 1/2 June 1983 : ID comb in ed RW and GHD flow s at Ru fford Pa rk
PEAK
12 . 700 CUMECS
140 0 GMT
1 TUN 8 3
• 5
0 .
24 0 . 2400 .
3 1 MAY 83 TI ME ( GMT)
• X—AXIS ZERO 2 40 0 GMT • • Z9 Reso urc e s d id no t perm it a deta iled invest ig atio n . How ev er , the wate r leve l record for 3 1 M ay / 2 Ju ne 1983 sh ow n in Fig . 7 .2 prov id e s som e co rrobo ration that the hy dro grap h sim u la tio n (F ig . 7 .1 ) is reasonable .
It is po ss ib le that the sim u la ted flood hy drog raph at Ru fford Pa rk is rather to o unifo rm . Eye-w itness acco unts su ggest that the temporal pattern of respo nse m ay hav e been rather m ore lik e tha t see n at Southw e ll , w ith the se cond storm prod uc ing a sub sid ia ry peak in the e arly hours o f 2 June 19 83 .
30 • • Fig . 7 .2 Observed le vel hyd rogra ph for 1/2 June 1983 : • Gre et at Sou th w ell • • PEAK
• 0 8 9 0 METRES
1130 GMT • • 0 . 8 1 TUN 8 3 •
• 0 . 6 • • • • •
24 0 . 2400 . • • 3 1 fl AY 83 -TI ME ( GMT1 • X- AXI S ZERO 2 40 0 GMT • • at • 8 SUmM A RY AN D ADD IT IONAL REMA RK S
.1 Ev ent rarit es
T he rar it ie s o f the flo od -p ro duc ing ev ent s on 22 April 1983 and 1/ 2 June 19 83 hav e been assessed .
22 A PR IL 1983
T he storm depth o f 17 .0 mm in 2 .25 hou rs on 22 Ap ril 1983 has a mean recurrence in te rv a l o f abou t 1 .25 years . T hu s it w as not a very ra re ev ent . T he resu ltqnt flood peak at Ru fford Lake is est im ated to be 8 .5 re s-Å , w ith an asse ssed m ean recu rre nc e inte rva l o f 2 .5 years . Simu latio n o f the event su ggests that ab out ha lf the flood runo ff emanated from the Ga llow Hole Dyke and ha lf from th e Rainw orth Wate r .
1/2 JU NE 19 83
Tw o storm s occu rred on 1 June 19 83 . The first storm w as much the la rger , w it h a m ean depth o f 28 .0 mm fa lling in 3 .5 hours ; th is has a mean recurrence in te rv al o f about 5 years . T he second storm was charac te rized by tw o in te nse but loc alized bursts of rain . A m ean depth o f 13 .8 mm fe ll in 2 .75 hours in th is second storm ; th is ha s a mean recurre nce interv a l o f about 7 months .
T aken together , the tw o storm s y ielded 43 .3 mm in 15 .5 hours . T his lo nger duratio n fa ll ha s a mea n re curre nc e interv a l o f about 5 .25 years . How ev er , be cause the ra in fall w as not u niform ly d ist r ibuted over the 15 .5 ho ur pe r iod , this asse ssm ent may be m is le ad in g .
In term s o f their in d iv idua l contr ibut ions , the simu la ted hyd ro gra ph for the Rainworth Water ha s a peak o f 7 .3 re s- s w ith a m ean recu rrence in terv a l of about ,10 years ; that for the Ga llow Ho le Dyke has a pea k o f 5 .3 ne $ - s , wit h a mean recurrence in terv al o f ab ou t 3 .5 years .
It has been possible to sim u la te th e flood ru no ff resu lt ing jo in tly from the two storms w hic h occ urred on 1 June 19 83 . T he estim ated flood hy drograph is sh own in Fig . 7 .1 .
T he s imu la t io n su gge st s that the pe ak comb in ed glow ,o f the Ra inworth Water and Gallow Ho le Dy ke w as 12 .7 m a s - 1 , occurr in g at ab ou t 14 .00 hr GMT on 1 Jun e , ie . abou t tw o hours prio r to commencem ent o f the second storm . This com b in ed pe ak flow h as a m ean recu rre nce in terv a l o f about 5 y ears . The syn thesis in d ic ates g at the to tal v o lum e o f event ru no ff was about 728 ,000 m a , w ith the Ra inw orth Wate r supp ly in g abo ut 60% and the Ga llow Hole Dy ke about 40% .
It can be seen that , wh ile the pea k flow was not exceptio na lly large , re la tiv e ly hig h flow s were ma in ta ined fo r a pro lo ng ed pe riod . Part ia l co rro bo ra t ion o f the hydrograp h shap e for the compos ite ev ent is prov id ed by the gauged record for the ad ja cent G reet at Southw e /1 ca tc hm ent (F ig . 7 .2 ). T h is share s som e geo logica l chara cte r is tic s w it h
32 •
• the comb ined Rainworth Water and G allow Hole Dy ke • catchm ents .
• It is possib le th at the simu la ted flood hydrograph at Ru ffo rd Park is ra ther too un iform . Eye -w itne ss ac cou nts • suggest that the tem poral patte rn o f response m ay hav e been rathe r more lik e tha t see n at Sou thw ell , with the se cond • storm p rod ucin g a su bsid iary peak in the ear ly ho urs o f 2 June 19 83 . 40 is to rica l otes
Autho rita t ive map p in g o f so ils for the 0 11ert on d is tr ic t 411 su ggests that , his torica lly (ie . prior to dra in age works , sub sidence , etc .), land in the v ic in ity o f Ma y lodge Dr ive • has been pro ne to flood ing from the Gallow Ho le Dy ke as well as from th e Ra inw orth Water . This is bec ause the fo rm er 411 catc hm ent is re lativ ely impe rm eab le and typ ica lly p roduces a gre ater flo od resp onse tha n the much more perm eab le 0 Ra inworth Water ca tc hm ent .
• As part o f the study , a h isto r ica l rev iew of la rg e ra in fa ll ev ents w as carr ied out by re ference to g auged ra in fa ll ID rec ord s and bac k-c op ies o f th e Mans fie ld CHAD new sp ap er . This rev ealed lit tle ev id ence o f past se rious flo od ing • incid ents in th e Rainworth Water catchm ent .
• It was no ted tha t th e Ra inwo rth Water came und er clo se scru t iny in the m id to la te 19 70s becau se of the sm alln ess • o f its flows . The per iod coinc ided w ith a large ly na tu ra l M lowerin g o f g roundwater leve ls in the reg ion . How ev er , the 41, lo ss o f riv er wate r to the und erly ing aq u ifer w as held by contempora ry rese arc h to be attribu tab le to fis su re s in the • super ficia l so ils . Deep m inin g is the m o st like ly cau se o f such fissu res . The abse nc e o f la rg e flow s in the Ra inw orth • Water dur ing the m id and late 1970s may have engend ere d a fa lse sen se o f se curity in te rm s o f flo od risk at Ru fford 411 Park . 40 . t f tors II It is conc luded that the meteo ro lo g ical condit io ns alo ne do not exp la in the very se r ious flood ing inc iden ts exp erie nc ed II at Ru fford Park on 22 April 19 83 and 1 June 19 83 . Exce ptio na l contr ib uting fac to rs m ust there fore be sought , 0 o f w hic h d ifferent ia l la nd su bsidence app ears to be the m ost like ly ro ot cau se . II Re so lu tio n o f liab ility may re st o n the s izing , II constru ctio n , m a intenanc e and inte grity o f eng in eered st ru ctures , no tably the embankm ents whic h interv ene betw een 0 M ay lodge Dr ive , th e vario us waterc ourses , and Ru fford Lake . Su rv ey s o f land , waterc ou rse and emb an km ent lev els , II investig atio n o f m in ing su bs id enc e , as sessments o f hy drau lic char acteris tic s o f the waterc ourse s and struct ures II (inc lud ing the out flow we ir at Ru ffo rd La ke ) m ay a ll be highly re levant . T he se are matters to w h ic h pro fe ss iona l 40 hydro lo g ical ad v ice is peripheral . • • 33 • T he hyd ro lo gic a l ass essm ent is that the 22 April 1983 and 1 June 19 83 flood ev ents w ere unexceptio nal . O the r facto rs must hav e bee n h ig hly in fluent ia l in a llow ing these mod er ate events to cause floo d ing and , in the case o f th e 1 June 1983 event , to produce such d isastrous consequences .
34 •
• RE FERENCES
41 Dale s M Y and Re ed D W (1989 ) Re g iona l flood and sto rm haza rd assessm ent . Rep ort No . 102 , Ins titu te o f 41 Hydro logy , 159pp .
41 F inch J W (1979 ) T he fu rther dev e lopm ent o f e lectr ica l resis tivity techniq ues for de term ining ground water 41 q uality . Ph .D . thes is , D ept . o f G eolog ic a l Sc iences , 40 Un iv . of B irm ingham , 225pp + Figures + Appe nd ices . Institu te o f G eo log ica l Science s (1981 ) Hydrogeo logica l 41 map o f the no rth ern East M id la nd s , 1:100000 sca le .
• Institute o f Hyd ro lo gy (1983 ) Assessing the re tu rn pe riod o f a nota ble flood . F lood Stud ie s Supp lementary 41 Report No . 12 , IH , 5p p .
ID Inst itute o f Hy d ro logy (1985 ) The FSR ra infa ll-runoff mod e l parameter est imatio n eq uatio ns upd ated . Flood Stud ies Supplementary Report No . 16 , IH , 5pp .
• Natu ra l Env ironm ent Researc h Cou nc il (1975 ) UK Flood Stud ies Repo rt . 5 vo lume s , N ERC . 111 Reed D W (198 7 ) Engaged on the ung auged : app lic ations o f 41 the FSR rain fa ll -ru no ff m ethod . Pr oc . 1s t Natio nal Hyd ro l . Symp ., Hu ll , Se p temb er 1987 , pp . 2 .1-2 .19 . 41 Rob son J D and Geo rge H (1971 ) So ils in Not tin gham shire • I : Sheet SK 66 (0 11e rto n ). Soil Su rvey Record No . 8 , 0 Soil Survey o f En g la nd and W a le s , 82pp + map (1 :250 00 41 sca le ).
• Roya l Socie ty (198 3 ) R isk assessment : repor t o f a Royal Soc ie ty Study G ro up . Ro ya l soc iety , Lond on . 41 So il Surv ey o f Eng la nd and Wa le s (198 3 ) Soils o f m id la nd 41 and weste rn Eng land (Shee t 3 ), 1:250000 scale .
41 So il Surv ey and Land Research Centre (19 87 ) G ro und water vu ln era bility map , Sev ern Trent Water , Sheet 6 : 41 Mans fie ld , 1 :100000 sca le .
41 Stewart E J (19 88a ) Ru ffo rd Park rain fa ll stu dy . Inst itute of Hy dro lo gy repor t to E lliott & Brown 41 consu lt ing engin eers , March 19 88 , llpp .
• Stewart E J (1988b ) Ru ffo rd Park ra infa ll study : fu rt her a na ly sis . Inst itu te o f Hy dro lo gy rep ort to Ell io tt & 41 Brow n con su lt in g eng ine er s , June 1988 , 5p p .
41 W ild W (1972 ) A br ie f recorded his to ry o f Blidw orth , in clud ing New ste ad and C lipst one . (Copy ava ilab le in 41 Mansfield L ibrary .) 41 • 41 41 "35 41 APPE ND IX 1 Flo od Studie s Rep ort nom en c latu re
AP IS ante cedent p rec ip itat io n index ov er 5 days , mm A REA ca tc hm ent area , km 4 CW I catch men t wetne ss ind ex (CW I= 125-SMD TAP I5 ), mm d esig n storm dura tio n , hr LA KE fr actio n o f catc hment d ra ining th rough a s ign ificant la ke or reserv o ir M SL ma in stream length , km M 5-2D 2-d ay ra in fa l l o f 5-y ear return period , mm QBA R m ean o f annua l maximum instanta ne ous flooq series , know n as th e w ean annual flood , m ' 5 - 1 base flow allowanc e , m s-1 DBA SE 3 - 1 QT flo od peak o f re tu rn pe riod T , m s ra tio o f 60-m inute ra in fall o f 5-y ea r retu rn per iod to M 5-2D , know n as Jenk inso n 's "r " RSM D 1-day catchm ent rain fa ll of 5-y ea r retu rn per iod le ss SM DBA R , mm SAA R (sta nd ard period ) av erage annua l ra in fa ll , mm SMD so il mo isture de fic it SMD BAR e ffect iv e mean va lue o f SMD SO IL 1 fractio n of catchm ent hav ing soil in cla ss 1 SO IL 4 fr actio n of catc hm ent hav ing sotl in cla ss 4 STM FRQ stream frequency , ju nc tiong km -4 S 1085 10 -858 strea m s lope , m km -s av era ge inte rv a l betw een yea rs w it h a flo od exceed in g a g iven m agn itud e , known as retu rn period (on annu a l max imum sca le ), y r Tp (0 ) tim e -t o-p eak of an eq u iv alent in st anta neous un it hyd rograph , hr URBA N fr actio n of catc hm en t urb anize d (m easu red from 1 :50 000 sc ale map )
36 411 411 A PPIENIXE7C 2 Ag r e e d r a i n f a l l v a l u e s 411
411 RIEFORD COUNTRY PARK NI GN COURT - - MEADOWS etc - v- NOTTS COUNTY COUNCIL 8RITISN CCUkl. CORPORATION 411 mEET1N6 OF EXPERTS - - AGENDA ITEM DI • Dai l y Rai nfal l Tot al s at var i ous St at i ons Wi t hin I Around t he Ruf for d Lake Catcheennt Ar ea on the Speci f i ed Dat es sn Apri l , May Junft 1983 • • : Stat i on : Stat i on Net .Of f . ' nat i onal Rai nf al l i n • i l l i eetr es ono • : Ref . : Name Ref . No. Gr i d Ref . 22 Apr 23 Apr 18 May 19 May 20 Nay ' 29 May 30 May 31 May I June 2 June
• Sut t on-in-Ashf i eld .411 6.41k6 Mansf i el d S. Wor ks
Bl i dwor t h.Ravenshead
Rai nwto t h Spr i ng Wi l l S.Wka Edwinstowe
Edwi nstowe W.R. Ilks
Bouolit on P. S.
Ruf f or d P.S.
Eakr i ng
Farnsf i eld
Tui f or d, Westwood
Reinwor t h
Par son Gl eadthor pe 'EWE Cl i pst ont N.V.
0 Mansf i el d
Br acki nhur st , S'wel l Not t s Col l of Av i d
• • • • • • • • • • H a . . . .M.0 .0 Me e M e e M a e • •• • • •;
VOTES.
I ) The Dai l y Rai nf al l Val ues r eprel ent t he &gaunt of r ai nf al l i n ei l l i setr es which f el l bet ween 0900 hr s 6112 an t he day indicat ed 0900 hr s U T on the f ol l owi ng day; •-c 22 The Measuri ng St at i on locat ions are shownwi th t hei r respecti ve R•ference Lett ers on Drawi ng D/00340/ 124 b
3) Est i mat ed dai l y val ues w or t h:4W by t he Nat Of f i ce fr o. sul t i day readi ngs are shoo suf f i xed 'el
41 The val ues i n parent heses f or St at i on I VI I accueul at edOVOf t he 7 days 20-22 hay & the 4 days 27-30 Day !• respect i vel y.1.; A PPEND IX 3 Rain fa ll rarity assessme n ts
A 3 .1 Genera l
The ra in fa ll ra rity assessm ents are m ade fo r the 75 .7 km 2 catc hm ent to Ru fford Lake (ca tc hm ent RL ). For each sto rm , the rarity asse ssm en t (Sectio n A 3 .3 ) is made by com pa ring an equ iv a le nt po int ra in fa ll (d erived in Sectio n A 3 .2 u sing the sto rm dep th s and durations found in Sections 3 and 4 ) w ith "design " po int ra in fall d epths o f the same dura tio n d erived for a ra nge o f retu rn pe r iods .
A .2 lcu la tio n o f e u iv a le nt oint ra i a 1
Sto rm date Catc hm ent Sto rm A real Eq u iv . av erage d urat io n reduc tio n po in t [no .] ra in fa ll fa ctor ra in fall (mm ) (hr ) (-) (mm )
22 Apr il 1983 17 .0 2 .25 0 .868 19 .6
1 Ju ne 19 83 : [1 ] 28 .0 3 .5 0 .890 3 1 .5 [2 ] 13 .8 2 .75 0 .878 15 .7 (" 1+2 1 ) 43 .3 15 .5 0 .939 4 6 .1
A . Rar it ass essm ents
Desig n ra in fa ll sta t is tic s : M 5-2D = 55 mm (se e Se ctio n 2 .3 ) r = 0 .402 (see Sectio n 2 .2 )
Ca lcu la tio n ta ble :
[A ] [B ]
Sto rm Depth Sto rm M 5-D hr Ratio Return Mean (ty p 'l dur 'n p o in t [A ] : per iod_ recur- po in t ) D depth [B ] rence (mm ) (hr ) (mm ) (y rs ) (mon th s )
22 Apr 19 .6 2 .25 27 .6 0.7 10 1 .81 15
1 Jun : [1 ] 31 .5 3 .5 30 .9 1.019 5 .33 58 [2 ] 15 .7 2 .75 29 .0 0 .54 1 1 .20 7 ["1+ 2 " ] 46 .1 15 .5 44 .5 1.036 5 .79 63
343 en it v t to v u e -20
Lo cally ad just ed est im ate s o f the M 5-2D rainfa ll sta tis tic w ere re com m end ed In Sec t ion 2 .3 . The ca lcula tion ta b le be low use s an "as mapped " v a lue o f M 5- 2D , to prov ide a check tha t th e ra rity a ssess ment s are re la tive ly insensit iv e to this ad justmen t .
M 5-2D fo r Ru fford Lake :
Pr e ferred estima te (used in Sectio n A3 .3 ): 55 mm "As mapped " est im ate (used be low ): 50 .5 mm
41 [A ] [B ] • Sto rm Dep th Sto rm M 5-D hr Ra t io Return Mean (typ 'l dur 'n poin t [A ] : p eriod recur- 0 poin t ) D dep th [B ] re nce (mm ) (hr ) (mm ) (yrs ) (month s )
22 Ap r 19 .6 2 .25 25 .3 0 .775 2 .33 2 1 41 I Ju n : • [1] 31 .5 3 .5 28 .3 1 .113 7 .22 81 [2 ] 15 .7 2 .75 26 .6 0 .590 1 .33 9 • [" 1+2 1 46 .1 15 .5 40 .8 1 .130 8 .29 93 • It is seen that the rarit ies assessed us ing th e "as mapp ed " est imates o f M 5- 2D a re ra ther g re ater than th ose • ob ta in ed earlie r . • However , for th e reasons g iven in Sec tio n 2.3 , the lo cally ad justed 145-2 0 va lues are pre ferred and the • asse ssmen ts o f Sectio n A 3 .3 there fore sta nd .
• • • • • 0 • • 39 APPEND IX 4 Com puter lis tings for hy d rogra ph simu la tio ns
d o ra h sim u la tions for 22 A ril 1 p . A 4 .1 : RL catchm ent p . A 4 .2 : GHD catchm ent p . A 4 .3 : RW catchm ent
d ro ra h sim u la tions for 1st storm o n 1 une 1 p . A 4 .4 : RL catc hm ent p . A 4 .5 : GHD catchm ent p . A 4 .6 : RW catchment
d ro ra sim u la t o s fo 2n d sto o n une p . A 4 .7 : RL catchment p . A 4 .8 : GHD catchm ent p . A 4 .9 : RW catchm ent
40 R 1L 1•111.5 Des cript ion : Ra inworth wat er at Ru ffo rd Lake Printed on 25- 1- 1990 at 14 .40 Run Referenc e - RLA KE
Co nv o lu tion o f use r defined rain fa ll
(UH op tion I) Un it hyd rograph time to pe ak 8 .7 hours ITP opt ion 0 ) Dat a in te rval 0 .50 ho urs
De s ign sto rm dura tion 2 .5 ho urs (Du r op tion 0 ) De s ign s to rm dep th 17 .60 mm . 17 op tion 0 ) De s ign CM I 131 .00 (CM I op tion 0 ) Sta nd ar d Pe rcen tage Ru no ff 19 .99 1SR R op tion 2 1 Pe rc en tage runo ff 22 .22 1 (PR option 1)
Re spons e hyd rog raph pe ak 6 .84 cumec s Das eflow 1 .70 cumec s (15ase flow optio n
De sign hyd rograph pe ak 8 .54 cumec s = = = = 3 2 7
n icro -F SR - Ins titu te of Hyd ro logy Ve rs ion 1.I-r (1.1-11-
I n s t i t u t e o f H y d r o l o g y
LK DES IGN FLOO D EST IMAT ION
T ime ser ies data from est imat e us ing th e Floo d Stud ies Rep ort re in fa ll -runo ff method
De sc ript ion : Rainwo rth w ater at Ru fford La ke lr in ted on 25 - 1- 1990 at 14 .40 Run Re ference - RLAKE
T ime c- - Ra infa ll - - ) Unit Tote / Pro fi le N et Hyd rograph AN SE Re sp on se Tota l ho urs mm i mm cum ecs /cm i cum ec s pe r 100sci km
1.7o 4 1 "- 1 7 . 1 0 k r 0 .50 5 .1 30 .0 1.1 1 .47 0 .26 1 .70 0 .11 1 .82 CilM T 1 .00 1 .7 10 .0 0 .4 2 .93 0 .53 1 .70 0 .29 1 .99 1.50 2 .5 15 .0 0 .6 4 .40 0 .79 1.70 0 .52 2 .22 2 .00 5 .1 30 .0 1.1 5 .87 1 .06 1 .70 0 .88 2 .58 2 .50 2 .5 15 .0 0 .6 7 .33 1 .32 1 .70 1 .30 3 .00 3 .00 8 .80 1 .58 1 .70 1 .72 3 .42 3 .50 10 .27 1 .85 1 .70 2 .14 1 .84 4 .00 11 .73 2 .11 1 .70 2 .56 4 .26 4 .50 13 .20 2 .38 1 .70 2 .98 4 .68 5 .00 14 .67 2 .64 1 .70 3 .40 5 .10 5 .50 16 .13 2 .90 1 .70 3 .82 5 .51 6 .00 17 .60 3 .17 1 .70 4 .24 5 .93 6 .50 19 .07 3 .43 1.70 4 .66 6 .35 7 .00 20 .53 3 .70 1 .70 5 .07 6 .77 7 .50 22 .00 3 .96 1 .70 5 .49 7 .19 8 .00 23 .47 4 .22 1 .70 5 .91 8 .50 24 .93 4 .49 1 .70 6 .33 8 .03 9 .00 24 .75 4 .45 1 .70 6 .61 8 .31 9 .50 23 .78 4 .28 1 .70 6 .77 8 .47 10 .00 22 .82 4 .11 1.70 6 .84 8 .54 11 .50 21 .85 3 .93 1 .70 6 .74 8 .44 11 .00 20 .69 3 .76 1 .70 6 .50 8 .19 11.50 19 .92 3 .59 1 .70 6 .22 7 .92 12 .00 18 .96 3 .4 1 1 .70 5 .94 7 .64 12 .50 17 .99 3 .24 1 .70 5 .67 7 .37 13 .00 17 .03 3 .06 1 .70 5 .39 7 .09 11 .50 16 .06 2 .89 1 .70 5 .12 6 .82 1 1.00 15 .10 2 .72 1 .70 4 .84 6 .54 14 .50 14 .13 2 .54 1 .70 4 .57 6 .26 15 .00 13 .17 2 .17 1 .70 4 .29 5 .99 15 .50 12 .20 2 .20 1 .70 4 .01 5 .71 16 .00 11 .24 2 .02 1 .70 3 .74 5 .44 16 .50 10 .27 1 .85 1.70 3 .46 5 .16 17 .00 9 .3 1 1 .68 1 .70 3 .19 4 .88 17 .50 8 .34 1 .50 1 .70 2 .91 4 .61 19 .00 7 .38 1 .33 1 .70 2 .63 4 .33 18 .50 6 .4 1 1 .15 1 .70 2 .16 4 .06 19 .00 5 .45 0 .98 1 .70 2 .08 3 .78 19 .50 4 .48 0 .81 1 .70 1 .81 1 .50 23 .00 3 .52 0 .63 1 .70 1 .53 3 .23 23 .50 2 .55 0 .46 1 .70 1 .25 2 .9 5 2 1.00 1.59 0 .29 1.70 0 .98 2 .68 2 1.50 0 .62 0 .11 1 .70 0 .70 2 .40 22 00 . 1 .70 0 .46 2 .15 2/.50 1 .70 0 .27 1 .97 21 .00 1 .70 0 .12 1 .82 23 50 1.70 0 .01 1 .71 PM-14.11-%'1N S De sc rip tion t callow Ho le Dyke to confluen ce with Rainwo rth Wate pr in ted on 3- 1- 1990 at 17 .51 RU n Re fer en ce - GH DDD 411
co nv olu tion o f us er de fine d ra in fa ll AA. 2 41 ==rriannsitniii.mcca=== Z Z 12 = = = = i n fl u n (UH op tion Un it hydr ogr aph time to peak 8 .4 hou rs (TP op tion 40 Dat a inte rv a l 0 .50 ho urs
Des ign storm du rat ion 2 .5 hou rs (Du r op tio n 40 De s ign sto rm de pth 20 .00 mm . (P op tion De s ign CW I 13 1 .00 (CW I op tio n Stan dard Pe rc en ta ge Ru no ff 47 .00 (SPR op tio n 411 Pe rc en tage ru no ff 48 .56 % (PR op tion 41 Re spo nse hyd rograp h p eak 3 .62 cum ecs Ba seflow 0 .32 cumecs 41 (nose flow option De s ign hyd ro gr ap h pe ak 2 .94 cu mecs 40 ======s
m icro -F SR - In st itu te o f Hy dro logy V ersion 1 .1 r (iii) 41
I n s t i t u t e o f H y d r O l o g y 41 UK DESIGN FLOO D ES TImA T ION
T ime Ser ies dat a from est imat e using th e 40 Flood Stud ie s Re po rt ra in fa ll-r unoff method 40 Des cr ip tion : C al low Ho le Dyke to con fluen ce w ith Rainwo rt h Mate Pr inted on 3- 1- 1990 at 17 .52 Ru n Re fere nce - GlIDDD 41 T im e <- - Rain fa ll --> Un it To ta l Pro fi le Net Hyd ro graph *N SF Re sponse T ota l 41 ho urs mm I. mm cum ec s/ cm % CUM8 C 6 pe r 100sg km 0 1 2 C7 . 3 636 c 41 0 .50 6 .0 30 .0 2 .9 1 .55 0 .28 0 .32 0 .07 0 .39 1 .00 2 .0 10 .0 1 .0 3 .10 0 .56 0 .32 0 .16 0 .48 41 1 .50 3 .0 15 .0 1 .5 4 .64 0 .84 0 .32 0 .29 0 .61 2 .00 6 .0 30 .0 2 .9 6 .19 1 .11 0 .32 0 .48 0 .80 2 .50 3 .0 15 .0 1 .5 7 .74 1 .39 0 .32 0 .7 1 1 .03 41 3 .00 9 .29 1 .67 0 .32 0 .94 1 .26 3 .50 10 .84 1 .95 0 .32 1 .17 1 .49 4 .00 12 .38 2 .23 0 .32 1 .39 1 .72 41 4 .50 13 .93 2 .51 0 .32 1 .6 2 1 .95 5 .00 15 .48 2 .79 0 .32 1 .85 2 .17 5 .50 17 .03 3 .06 0 .32 2 .08 2 .40 40 6 .00 18 .57 3 .34 0 .32 2 .31 2 .63 • 6 .50 20 .12 3 .62 0 .32 2 .54 2 .86 7 .00 21 .67 3 .90 0 .32 2 .77 3 .09 7 .50 23 .22 4 .18 0 .32 2 .99 3 .32 8 .00' 24 .77 4 .46 0 .32 3 .22 3 .54 41 8 .50 25 .95 4 .67 0 .32 3 .43 3 .76 9 .00 24 .94 4 .49 0 .32 3 .54 3 .87 9 .50 23 .92 4 .30 0 .32 3 .61 3 .94 41 10 .00 22 .90 4 .12 0 .32 3 .62 3 .94 10 .50 21 .88 3 .94 0 .32 3 .52 3 .84 11 .00 20 .86 3 .76 0 .32 3 .37 3 .69 11 .50 19 .84 3 .57 0 .32 3 .22 3 .54 /2 .00 28 .83 3 .39 0 .32 3 .0 7 3 .39 12 .50 17 .81 3 .21 0 .32 2 .9 1 3 .24 41 13 .00 16 .79 3 .02 0 .32 2 .76 3 .09 13 .50 15 .77 2 .84 0 .32 2 .61 2 .94 41 14 .00 14 .75 2 .66 0 .32 2 .46 2 .79 14 .50 13 .73 2 .47 0 .32 2 .31 2 .64 15 .00 12 .72 2 .29 0 .32 2 .16 2 .49 15 .50 11 .70 2 .11 0 .32 2 .01 2 .34 16 .00 10 .68 1 .92 0 .32 1 .86 2 .19 16 .50 9 .66 1 .74 0 .32 1 .7 1 2 .03 41 17 .00 8 .64 1 .56 0 .32 1 .56 1 .88 17 .50 7 .62 1 .37 0 .32 1 .4 1 1 .73 18 .00 6 .61 1 .19 0 .32 1 .26 1 .58 18 .50 5 .59 1 .01 0 .32 1 .11 1 .43 19 .00 4 .57 0 .82 0 .32 0 .96 1 .28 19 .50 3 .55 0 .64 0 .32 0 .8 1 1 .23 41 20 .00 2 .53 0 .46 0 .32 0 .66 0 .98 20 .50 1 .51 0 .27 0 .32 0 .51 0 .83 21 .00 0 .50 0 .09 0 .32 0 .36 0 .68 41 21 .50 0 .3 2 0 .23 0 .55 22 .00 0 .32 0 .13 0 .46 22 .50 0 .32 0 .06 0 .38 41 23 .00 0 .32 0 .0 1 0 .33 41
m icro -FSR In st itute o f Hydro logy Ve rs ion 1.1 r (ii il 41 4 2 14%..> Des cript ion : Ra inworth Wa ter at con fluence w ith C al low Ho le Dyk Pr inted on 3- 1- 1990 at 17 .15 RUn Re ferenc e - RWWW W
Co nvo lu tion o f use r de fin ed ra in fall ======e t n e c e s ===rn e ======e m= A4-1 N H op tion Un it hy dro gr aph t ime to pe ak 8 .4 hours (TP op tion Data interval 0 .50 hou rs
De s ign storm du ra t ion 2 .5 ho urs O ur op tion De sign storm de p th : 16 .00 mm . IP op tion De sign cw I : 131 .00 (CW I option St and ard Percen ta ge Ru no ff : 12 .96 (SPA op tion Pe rcen tage runo ff 15 .63 (PR op tion
Re spon se hydro graph pe ak 3 .64 sum acs Base flow 1 .25 cumec s (Baseflow op tion
De s ign hyd rogr ap h peak 4 .89 cum ecs = = = = 3 C M
m icro -p si - Institute o f Hyd ro logy Vers ion 1 .1 r (iii) • 1-
I n s t i t u t e o f H y d r o l o g y
UK DES IGN FLOO D EST IMAT ION
T ime Ser ies dat a from estimate using the Flood Stud ies Report ra in fa ll-run o ff metho d
De sc ription : Ra inw orth W at er at ronfluenc e w ith G al low Hole Dyk Pr in ted on 3- 1- 1990 at 17 .16 Run Re fe rence - RWWWW
T ime c-- Ra infa ll - - > Unit (- -- - Flow --- -> Tota l Pro fi le Ne t Hyd rograph AN SF Re spo nse To ta l ho u rs mm 1. mm cu me cs /cm % cum ecs per 100 sg km
0 .50 4 .8 30 .0 0 .8 1.57 0 .28 1.25 0 .07 1.32 1 .00 1 .6 10 .0 0 .3 3 .14 0 .57 1 .25 0 .16 1.41 1 .50 2 .4 15 .0 0 .4 4 .71 0 .85 1 .25 0 .29 1 .54 2 .00 4 .8 30 .0 0 .8 6 .28 1 .13 1 .25 0 .49 1 .74 2 .50 2 .4 15 .0 0 .4 7 .85 1 .41 1 .25 0 .72 1 .97 3 .00 9 .42 1 .70 1 .25 .0 .95 2 .20 3 .50 10 .99 1.98 1 .25 1 .18 2 .43 • 4 .00 12 .56 2 .26 1 .25 1 .41 2 .67 4 .50 14 .13 2 .54 1 .25 1 .64 2 .90 5 .00 15 .70 2 .83 1 .25 1 .88 3 .13 5 .50 17 .27 3 .11 1 .25 2 .11 3 .36 6 .00 18 .84 3 .39 1 .25 2 .34 3 .59 6 .50 20 .41 3 .67 1 .25 2 .57 3 .82 7 .00 21 .98 3 .96 1 .25 2 .80 4 .06 7 .50 23 .55 4 .24 1 .25 3 .03 4 .29 8 .00 , 25 .12 4 .52 1 .25 3 .27 -,..-, 4 .52 8 .50 26 .02 4 .68 1 .25 3 .47 4 .72 9 .00 24 .98 4 .50 1 .25 3 .57 4 .83 9 .50 23 .95 4 .31 1 .25 3 .64 4 .89 10 .00 22 .92 4 .12 1 .25 3 .63 4 .88 10 .50 21 .88 3 .94 1 .25 3 .52 4 .77 11 .00 20 .85 3 .75 1 .25 3 .37 4 .6 2 11 .50 19 .82 3 .57 1 .25 3 .21 4 .47 12 .00 18 .78 3 .38 1 .25 3 .06 4 .31 12 .50 17 .75 3 .20 1 .25 2 .91 4 .16 13 .00 16 .72 3 .01 1 .25 2 .76 4 .0 1 13 .50 15 .69 2 .82 1 .25 2 .60 3 .86 14 .00 14 .65 2 .64 1 .25 2 .45 3 .70 14 .50 13 .62 2 .45 1 .25 2 .30 3 .55 15 .00 12 .59 2 .27 1 .25 2 .15 3 .40 15 .50 11 .55 2 .08 1 .25 1 .99 3 .25 16 .00 10 .52 1 .89 1 .25 2 .84 3 .09 /6 .50 9 .49 1 .71 1 .25 1 .69 2 .94 17 .00 8 .46 1 .52 1 .25 1 .54 2 .79 17 .50 7 .42 1 .34 1 .25 1 .38 2 .64 18 .00 6 .39 1 .15 1 .25 1 .23 2 .48 • 18 .50 5 .36 0 .96 1 .25 1 .08 2 .33 /9 .00 4 .32 0 .78 1 .25 0 .93 2 .18 19 .50 3 .29 0 .59 1 .25 0 .77 2 .03 20 .00 2 .26 0 .41 1 .25 0 .62 1 .88 20 .50 1 .22 0 .22 1 .25 0 .47 1 .72 21.00 0 .19 0 .03 1 .25 0 .32 1 .57 21 .50 1 .25 0 .20 1 .46 22 .00 1 .25 0 .11 1 .36 22 .50 1 .25 0 .04 1 .29 23 .00 1 .25 0 .00 1 .26
• 1cro-r8R - In st itu te o f Hydro logy ve rsio n 1.1 43 I ; F t 4 4 t M ISS LI J Desc rip tion : Ra inwo rth W ater at Ru fford La ke prin ted on 25 - 1- 1990 at 14 .3 1 Run Re feren ce - RLA KE
Cc nvo lu tio n o f use r de fined ra in fa ll 22 2 2 2 2 2 A4-.4 (UH Op t ion 1) Un it hy dro graph t ime to peak 8 .7 hou rs (TP op tion 0 ) Dat a in terv al 0 .50 hou rs
Design sto rm dur at ion 4 .0 ho ur s (Dur op tion 0 ) Des ign storm dep th 2) .20 mm . (P opt ion 0 ) Des ign cM I 128 .00 (CMI op tion 0 ) Standard Pe rc enta ge Ru no ff 19 99 . (SPR o ption 2 ) Pe rc en ta ge runo ff 21.48 4 (PR op t ion 1)
Re spons e hy d ro gr ap h pe ak 10 .97 cumecs Base flow 1.62 cumecs (Base flow op t ion
Des ign hyd ro graph peak 12.59 cumecs
m ic ro -F SR - Institu te o f Hyd ro lo gy Ve rs ion 1 .1 r(ii i)
I n s t i t u t e o f H y d r o l o g y
UK DESIGN FLOO D EST IMAT ION
T ime se rie s dat a from estimate us ing the Flood Stud ies Repo rt ra in fall-runo ff method
De sc r iption : Rainw orth W ate r at Ru fford La ke Printed on 25- 1- 19 90 at 14 .32 Run Re ferenc e - RLAKE
T ime <-- Rain fa ll -- > Unit <-- -- Flow ---- > Total Pro fi le Ne t Hydrograph AN SF Response To ta l ho urs mm % mm cu mecs/cm % cu me cs pe r 100sq km I .62 -4- 0 3 -310 h r 0 .50 5 .3 18 .0 1.1 1 .47 0 .26 1.62 0 .13 1 .75 1.00 4 .4 15 .0 0 .9 2 .93 0 .53 1.62 0 .36 1.98 1 .50 1 .8 6 .0 0 .4 4 .40 0 .79 1.62 0 .63 2 .25 2 .00 3 .5 12 .0 0 .8 5 .87 1 .06 1 .62 0 .98 2 .61 2 .50 3 .8 13 .0 0 .8 7 .33 1 .32 1.62 1 .43 3 .05 3 .00 4 .7 16 .0 1 .0 8 .80 1 .58 1 .62 1.98 3 .61 3 .50 4 .7 16 .0 1 .0 10 .27 1 .85 1.62 2 .65 4 .28 4 .00 1 .2 4 .0 0 .3 11.73 2 .11 1.62 3 .35 4 .97 4 .50 13 .20 2 .38 1.62 4 .05 5 .67 5 .00 14 .67 2 .64 1.62 4 .74 6 .37 5 .50 16 .13 2 .90 1.62 5 .44 7 .06 6 .00 17 .60 3 .17 1.62 6 .14 7 .76 6 .50 19 .07 3 .43 1 .62 6 .83 8 .45 7 .00 20 .53 3 .70 1.62 7 .53 9 .15 7 .50 22 .00 3 .96 1.62 8 .22 9 .85 8 .00 23 .47 4 .22 1.62 8 .92 r0 :54 8 .50 24 .93 4 .49 1.62 9 .62 21 .24 9 .00 24 .75 4 .45 1.62 10 .17 11 .80 9 .50 23 .78 4 .28 1.62 10 .54 12 .17 10 .00 22 .82 4 .21 1.62 10 .81 12 .43 10 .50 2 1 .85 3 .93 1.62 10 .96 12 .59 11 .00 20 .89 3 .76 1.62 10 .97 12 .59 /1.50 19 .92 3 .59 1.62 10 .80 12 .42 12 .00 18 .96 3 .41 1.62 10 .45 12 .07 12 .50 17 .99 3 .24 1 .62 10 .00 11 .63 13 .00 17 .03 3 .06 1.62 9 .55 11 .17 13 .50 16 .06 2 .89 1.62 9 .09 10 .71 14 .00 15 .10 2 .72 1.62 8 .63 10 .25 14 .50 14 .13 2 .54 1.62 8 .17 9 .80 15 .00 13 .17 2 .37 1.62 7 .72 9 .34 15 .50 12 .20 2 .20 1.62 7 .26 8 .88 16 .00 11 .24 2 .02 1.62 6 .80 8 .42 16 .50 10 .27 1 .85 1.62 6 .34 7 .96 17 .00 9 .31 1 .68 1.62 5 .88 7 .50 17 .50 8 .34 1 .50 1.62 5 .42 7 .05 18 .00 7 .38 1 .33 1.62 4 .96 6 .59 18 .50 6 .41 1 .15 1.62 4 .51 6 .13 11 19 .00 5 .45 0 .98 1.62 4 .05 5 .67 19 .50 4 .48 0 .81 1.62 3 .59 5 .21 20 .00 3 .52 0 .63 1.62 3 .13 4 .76 20 .50 2 .55 0 .46 1 .62 2 .67 4 .30 2 1.00 1.59 0 .29 1.62 2 .22 3 .84 21 .50 0 .62 0 .11 1.62 1.76 3 .38 • 22 .00 1.62 1 .33 2 .95 22 .50 1.62 0 .98 2 .60 23 .00 1.62 0 .68 2 .30 23 .50 1.62 0 .42 2 .04 24 .00 1.62 0 .22 1 .84 24 .50 1.62 0 .08 1 .70 25 .00 1.62 0 .0 2 1 .64 De sc riptioa : Callow Ho e Dy e to co n ue nce w it a inwo rtn a e Pr inted cn 25 - 1-19 90 at 12 .10 Ru n Re feren ce - CHDD D co nv o lu tion o f use r defined ra in fa ll
(UH opt ion 1) A4.5 un it hydrog raph time to pea k 8 .4 hou rs (TP op tion 0 ) Data Inte rv a l 0 .50 hou rs
De s ign st orm du ra t ion 4 .0 hou rs (Dur op t ion 0 ) De s ign st orm dep th 29 .20 mm . (P op tion 0 ) Des ign CW I 128 .00 (Cm l op tion 0 ) Standard Pe rcen tage Runo ff 47 .00 (SPR op tion 2 ) Pe rcen tage runo ff 47 .82 % (PR op tion 1)
Re spo nse hy d rog raph pe ak 5 .03 cum ec s Base flow 0 .31 cumec s (Base flow op tion
Des ign h ydr ogr aph p eak 5 .34 cumec s m icro-FS R - Institu te o f Hy dro lo gy Ve rs ion 1 .1 r(iii)
I n s t i t u t e o f H y d r o l o g y
UK DE S IGN F1.000 EST IMATION
T ime Se r ies date from es timate using th e Floo d Stud ies Report ra in fa ll-runo ff method
De sc r ip tion : Cal low Hole Dy ke to co n flu en ce w ith Ra inwo rth Mate Pr inte d on 25- 1- 199 0 at 12 .10 Ru n Re fer ence - GHDD D
T ime <- - Ra in fa ll -- > Un it Tota l Pro fi le Net H ydro gr aph AN SF Re spo nse To ta l ho urs mm % mm cu mec s/cm % cum ec s pe r 10 0s q km
0 .1i4 o 33 66c 0 .50 5 .3 18 .0 2 .5 1 .55 0 .28 0 .31 0 .06 0 .37 am / 1 .00 4 .4 15 .0 2 .1 3 .10 0 .56 0 .3 1 0 .1 7 0 .48 1 .50 1 .8 6 .0 0 .8 4 .64 0 .84 0 .31 0 .30 0 .60 2 .00 3 .5 12 .0 1 .7 6 .19 1 .11 0 .3 1 0 .46 0 .77 2 .50 3 .8 13 .0 1 .8 7 .74 1 .39 0 .31 0 .67 0 .98 5 .00 4 .7 16 .0 2 .2 9 .29 1 .67 0 .3 1 0 .94 1 .24 2 .50 4 .7 16 .0 2 .2 10 .84 1 .95 0 .3 1 1 .25 1 .56 4 .00 1.2 4 .0 0 .6 12 .38 2 .23 0 .3 1 1.58 1 .89 4 .50 13 .93 2 .51 0 .3 1 1 .9 1 2 .22 5 .00 15 .48 2 .79 0 .31 2 .24 2 .54 5 .50 17 .03 3 .06 0 .3 1 2 .57 2 .87 6 .00 18 .58 3 .34 0 .3 1 2 .89 3 .20 C .50 20 .12 3 .62 0 .31 3 .22 3 .53 / .00 21 .67 3 .90 0 .31 3 .55 3 .86 7 .50 23 .22 4 .18 0 .31 3 .88 4 .19 8 .00 24 .77 4.46 0.31 4 .21 4 .52 a .50 25 .95 4 .67 0 .31 4 .52 c4 .8 3 9 .00 24 .94 4 .49 0 .31 4 .74 5 .05 9 .50 23 .92 4 .30 0 .3 1 4 .89 5 .19 10 .00 22 .90 4 .12 0 .31 4 .99 5 .30 13 .50 21 .88 3 .94 0 .31 5 .03 5 .34 11 .00 20 .86 3 .76 0 .31 5 .00 5 .31 11 .50 19 .84 3 .57 0 .31 4 .88 5 .19 12 .00 18 .83 3 .39 0 .3 1 4 .68 4 .99 12 .50 17 .81 3 .21 0 .31 4 .47 4 .78 13 .00 16 .79 3 .02 0 .31 4 .25 4 .56 13 .50 15 .77 2 .84 0 .31 4 .04 4 .34 14 .00 14 .75 2 .66 0 .31 3 .82 4 .13 14 .50 13 .74 2 .47 0 .31 3 .60 3 .91 15 .00 12 .72 2 .29 0 .31 3 .39 3 .70 15 .50 11 .70 2 .11 0 .31 3 .17 3 .48 16 .00 10 .68 1 -92 0 .31 2 .96 3 .26 /6 .50 9 .66 1 .74 0 .3 1 2 .74 3 .05 17 .00 8 .64 1 .56 0 .31 2 .5 2 2 .83 17 .50 7 .63 1 .37 0 .31 2 .3 1 2 .62 18 .00 6 .61 1 .19 0 .31 2 .09 2 .40 18 .50 5 .59 1 .01 0 .31 1 .88 2 .18 19 .00 4 .57 0 .82 0 .31 1 .66 1 .97 19 .50 3 .55 0 .64 0 .31 1 .44 1 .75 20 .00 2 .53 0 .46 0 .31 1 .23 1 .53 20 .50 1 .51 0 .27 0 .31 1 .01 1 .32 21.00 0 .50 0 .09 0 .31 0 .79 1 .10 Z1 .50 0 .31 0 .60 0 .91 22 .00 0 .31 0 .44 0 .75 22 .50 0 .31 0 .30 0 .61 23 .00 0 .31 0 .18 0 .49 23 .50 0 .3 1 0 .09 0 .40 24 .00 0 .31 0 .03 0 .34 24 .50 0 .31 0 .00 0 .31
4 5 3 t-I4t: mt S1_'.1 Des crip t ion , P air:worth W ater at co nfluence w ith cal low Ho le Dy k Printe d o n 25 - 1-19 90 at 12 .22 Run Re fere nc e - RW WW W A4 . 6 con vo lu ti on of us er def in ed ra in fal l r=22===inp=nr. 7C3flUir...= (UR option I) Un it hyd ro grap h t ime to peak 8 .4 ho u rs (TP op tion 0 ) Dat a interv al 0 .50 ho u rs
Design sto rm du ra tion 4 .0 ho u rs (Dur op tion 0 ) De sign sto rm dep th 29 .20 mm . (P op tion 0 ) De s ign CW I 128 .00 (CM/ op tion 0 ) Standard Percentage Runo ff 12 .96 (SPR op tion 2 ) Pe rcen tag e ru no ff 14 .89 % (PR option 1 )
Re sp on se hyd ro graph pea k 6 .12 cu m ec s Bese t/ow 1 .19 cu mec s (8ase flow op t ion
Design hy dro gr aph pe ak 7 .32 cu mec s
m ic ro -FE R - Institu te o f Hyd ro logy Ve rs ion _1 .1 r (iii )
I n s t i t u t e o f H y d r o l o g y
UK DES IGN FLOO D EST IMA T ION
T ime Se r ies d at a from est ima te using th e Flood Stu d ies Report ra in fall-runo ff m etho d
De sc rip t ion : Rainwo rth W ater at co nflue nc e w ith Gal low Ho le Dyk Pr inte d on 25- 1- 1990 at 12 .23 Run Refere nce - RWWWW
T ime <-- Rain fa ll --> Unit <- -- - Flow ---- > To ta l Pro fi le Net Hyd ro graph AN SI Re sponse To ta l ho urs mm % mm cum ec s/cm % cum ec s Desc r ip tion : Ra inw or th wate r at Ru ffo rd Lake T Utg V:t.Z 3 112. Pr inted on 25 - 1- 1990 at 14 .36 Run Re ferenc e - RLA KE A4 .7
Co nv o lution o f us e r de fined ra in fall
(UH op t ion 1) Un it hy dro graph t im e to peak 8 .7 hours (TP op tion 0 ) Da ta In te rv al 0 .50 ho urs
De sign sto rm du ra tion 3 .0 hours (bu r op tion 0 ) De stqn sto rm dep th 14 .10 mm . 1P opt ion . 0 ) De s ign CW I 149 .50 (CM / op t ion 0 ) Standard Percen ta ge Runo ff 19 .99 (SPR op t ion 2 ) Pe rcenta ge runoff 26 .77 % (PR op t ion 1 )
Re sPonse hydrogra ph pe ak 6 .60 cumecs Base flow 2 .16 cum ecs (Base flow optio n
De sign .hyd rog raph pe ek 8 .76 cum ecs • = = = = =. 3 . d icro -F SR - inst itu te o f Hyd ro logy Ve rs io n 1.1 r (111.)
I n s t i t u t e o f H y d r o l o g y
UK DES IGN FLOO D EST ImAT ION
T ime Se r ies data from es t imate using th e Floo d Stud ies Rep o rt ra in fa ll-r un o ff me thod
De scr ip tion : Ra lnworth Wate r at Ru fford Lake Pr inted on 25- 1-19 90 at 14 .37 Run Re fe rence - RLA KE
T ime <- - Rain fall --> Un it <--- - Flow --- - > Tota l Pro file Net Hydro gr aph AN SF Re sponse Tota l ho urs cm % mm cumecs/cm % cu m ec s
1 . 16 -*-- IW Oh e 2 .16 0 .08 2 .24 2 .16 0 .31 2 .47 Greilr 2 .16 0 .54 2 .7 1 2 .16 0 .78 2 .94 2 .16 1 .06 3 .22 2 .16 1 .48 3 .64 2 .16 1 .90 4 .06 2 .16 2 .32 4 .48 2 .16 2 .74 4 .90 2 .16 3 .16 2 .16 5 .74 2 .16 3 .99 6 .16 2 .26 4 .4 1 6 .57 2 .16 4 .83 6 .99 2 .16 5 .25 7 .41 2 .16 5 .67 '7 .83 2 .16 6 .09 8 .25 2 .16 6 .42 8 .58 2 .16 6 .54 8 .70 2 .16 6 .57 8 .73 2 .16 6 .60 8 .76 2 .16 6 .56 8 .74 2 .16 6 .37 8 .54 2 .16 6 .10 8 .26 2 .16 5 .82 7 .98 2 .16 5 .55 7 ./1 2 .16 5 .27 7 .43 2 .16 5 .00 7 .16 2 .16 4 .72 6 .88 2 .16 4 .44 6 .60 2 .16 4 .17 6 .33 2 .16 3 .89 6 .05 2 .16 3 .62 5 .78 2 .16 3 .34 5 .50 2 .16 3 .07 5 .23 2 .16 2 .79 4 .95 2 .16 2 .51 4 .67 2 .16 2 .24 4 .40 2 .16 1 .96 4 .12 2 .16 1 .69 3 .85 2 .16 1 .41 3 .51 2 .16 1 .14 3 .30 2 .26 0 .86 3 .02 2 .16 0 .60 2 .76 2 .16 0 .4 / 2 .57 2 .16 0 .29 2 .45 2 .16 0 .17 2 .33 2 ./6 0 .06 2 .22
4 =7 Le sc r ip tio n : callow H o le Dy ke to con fluen ce w ith Ra inw o rth M ate Pr in ted on 25- 1- 199 0 at 12 .06 Run Re feren ce - OH DD D co nv o lu tion o f u se r de fin ed rain fa ll ======.. =--=-- -- . ======(UH op tion Un it hydro gr ap h time to peak 8 .4 hours (TP option D ata Inte rv a l 0 .50 hou rs
Design st orm du ra tion 3 .0 ho u rs (Du r op tion De sign sto rm dep th /0 .00 mm . (P op tion Des ign CW I 149 .50 (CW I option Stand ard Fe rcen tt ge Ru no ff 47 .00 (SPR op tion Per ce ntage ru no ff 53 .18 (PR option
Re spo nse hy dro graph peak 1 .91 cu m ecs Base flow 0 .42 cu mecs (Bas eflow op tion
Des ign hyd rog rap h p ea k 2 .33 cum ecs ======u m icro -F SR 7 Institute of Hyd ro logy V ers ion 1 .1 r (ii i )
I n s t i t u t e o f H y d r o l o g y
UK DESIGN FLO OD EST IMAT ION
T ime se r ies data from es tima te using the Flood Stu dies Report ra infa ll- runo ff method
De sc r ip tion : C allow Hole Dyke to co n fluen ce w ith R ainw or th wate Pr in ted on 25- 1- 19 90 at 12 .06 Ru n Refer ence - GH DDD
T ime <-- Ra in fa ll -- > Un it <- --- Flow -- -- , Total Pro file Net Hyd rogr ap h ANSI Respo n se Tota l hours mm % mm cum ec s/cm % cumecs per 100sq km o 42.•-usrbh, 0 .50 1 .8 18 .0 1 .0 1 .55 0 .28 0 .42 0 .0 2 0.44 to"I 1.00 3 .8 38 .0 2 .0 3 .10 0 .56 0 .42 0 .09 0 .51 1 .50 0 .0 0 .0 0 .0 4 .64 0 .84 0 .42 0 .16 0 .58 2 .00 C .0 0 .0 0 .0 6 .19 1 .11 0 .42 0 .23 0 .65 2 .50 1 .1 11 .0 0 .6 7 .74 1 .39 0 .42 0 .3 2 0 .73 3 .00 3 .3 33 .0 1 .8 9 .29 1 .6 7 0.42 0.44 0 .86 3 .50 10 .84 1 .95 0 .42 0 .57 0 .98 4 .00 12 .38 2 .23 0 .4 2 0 .69 1 .11 4 .50 13 .93 2 .51 0 .42 0 .82 1 .23 5 .00 15 .48 2 .79 0 .42 0 .94 1 .36 5 .50 17 .03 3 .06 0 .42 1 .07 1 .48 6 .00 18 .58 3 .34 0 .4 2 1 .19 1 .61 6 .50 20 .12 3 .62 0 .42 1 .32 1.73 7 .00 21 .67 3 .90 0 .42 1 .44 1 .86 7 .50 23 .22 4 .18 0 .42 1 .57 1 .98 8 .00 24 .77 4 .46 0 .4 2 1 .69 .4. 2.11 8 .50 25 .95 4 .67 0 .4 2 1 .81 2 .23 9 .00 24 .94 4 .49 0 .42 1 .89 2 .30 9 .50 23 .92 4 .30 0 .4 2 1 .90 2 .31 10 .00 22 .90 4 .12 0 .4 2 1 .91 2 .32 10 .50 21 .88 3 .94 0 .4 2 1 .9 1 2 .33 11 .00 20 .86 3 .76 0 .4 2 11 .50 19 .84 3 .57 0 .4 2 1 .81 2 .22 12 .00 18 .83 3 .39 0 .4 2 1 .72 2 .14 12 .50 17 .81 3 .21 0 .4 2 1 .64 2 .06 13 .00 16 .79 3 .02 0 .4 2 1 .56 1 .98 13 .50 15 .77 2 .84 0 .4 2 1 .4 8 1 .89 14 .00 14 .75 2 .66 0 .4 2 1 .40 1 .81 14 .50 13 .74 2 .47 0 .4 2 1 .3 1 1 .73 15 .00 12 .72 2 .29 0 .4 2 1 .23 1 .65 15 .50 11 .70 2 .11 0 .4 2 1 .15 1 .56 16 .00 10 .68 1 .92 0 .4 2 1 .07 1 .48 16 .50 9 .66 1 .74 0 .42 0 .98 1 .40 17 .00 8 .64 1 .56 0 .4 2 0 .90 1 .32 17 .50 7 .63 1 .37 0 .4 2 0 .82 1 .24 18 .00 6 .61 1 .19 0 .4 2 0 .74 1 .15 18 .50 5 .59 1 .01 0 .4 2 0 .6 5 1 .07 19 .00 4 .57 0.82 0.4 2 0 .57 0 .99 19 .50 3 .55 0 .64 0 .42 0 .49 0 .91 20 .00 2 .53 0 .46 0 .4 2 0 .4 1 0 .82 20 .50 1 .51 0 .27 0 .4 2 0 .33 0 .74 21 .00 0 .50 0 .09 0 .42 0 .24 0 .66 21.50 0 .4 2 0 .17 0 .58 22 .00 0 .4 2 0 .12 0 .53 22 .50 0 .42 0 .08 0 .50 23 .00 0 .4 2 0 .04 0 .46 23 .50 0 .4 2 0 .0 1 0 .43
* is UN :e sc ription : Ra inwo rth wa ter at co nflue nce w ith Cal low Ho le Dy k Printe d on 25- 1- 1990 at 12 .19 Run Re ferenc e - RW ww w AA- Co nv o lu tion o f use r defined ra in fa ll M (UH op tion Un it hyd ro gra ph time to pe ak 8 .4 ho ur s (TP op tion Da ta in terv a l 0 .50 ho urs
Le sion storm du ra tion 3 .0 ho urs (Dur op tion Des ign sto rm dep th 15 .00 mm . (P op tion Des ign cw i 149 .50 (CW I op tion Stan dar d Pe rcentag e Runo ff 12 .96 (SPR option Pe rcen tage runo ff 20 .15 (PR op tion
Re sponse hy d rograph peak 4 .25 cum ec s bas e flow 1 .61 cum ec s (Baseflow op tion
De s ign hy dro gra ph pe ak 5 .86 cumec s
M ic ro -Fs p - Inst itute o f Hyd ro logy Ver s ion 1.1 r (iii ) _
I n s t i t u t e o f H y d r o l o g y
UK DESIGN FLOO D EST IMAT ION
T ime Series dat a from es tim ate us ing the Flood Stud ies Repo rt ra in fa ll -run off m etho d
De sc r iption : Ra inworth Wate r at co nflue nce w ith Gallow Ho le Dyk Pr in ted on 25 - 1-19 90 at 12 .20 Run Re ference - RWWW W
T ime C- - Rain fall - - > Unit To ta l Pro fi le Net Hyd rograph AN SF Re spo nse To ta l hours mm mm cumec s/cm % cu mecs Per 100sq km
(4 .1e-11.00 V4C 0 .50 2 .7 18 .0 0 .5 1 .57 0 .28 1.61 0 .05 1 .66 1 .00 5 .7 38 .0 1 .1 3 .14 0 .57 1.61 0 .21 1 .82 1 .50 0 .0 0 .0 0 .0 4 .71 0 .85 1 .61 0 .36 1 .98 2 .00 0 .0 0 .0 0 .0 6 .28 1 .13 1 .61 0 .52 2 .13 2 .50 1.6 11 .0 0 .3 7 .85 1 .41 1 .61 0 .71 2 .32 3 .00 5 .0 33 .0 1 .0 9 .42 1 .70 1 .61 0 .99 2 .60 3 .50 10 .99 1 .98 1.6 1 1 .27 2 .88 4 .00 12 .56 2 .26 1 .61 1 .55 3 .16 4 .50 14 .13 2 .54 1 .61 1 .83 3 .44 5 .00 15 .70 2 .83 1.61 2 .11 3 .72 5 .50 17 .27 3 .11 1 .61 2 .39 4 .00 6 .00 18 .84 3 .39 1 .61 2 .67 4 .28 6 .50 20 .41 3 .67 1 .61 2 .95 4 .56 7 .00 21.98 3 .96 1 .61 3 .23 4 .84 7 .50 23 .55 4 .24 1 .61 3 .51 5 .12 8 .00 25 .12 4 .52 1 .61 3 .79 8 .50 26 .02 4 .68 1 .61 4 .05 5 .66 9 .00 24 .98 4 .50 1 .61 4 .20 5 .81 9 .50 23 .95 4 .31 1.61 4 .22 5 .83 10 .00 22 .92 4 .12 1.61 4 .24 5 .85 10 .50 21 .88 3 .94 1 .61 4 .25 5 .86 11 .00 20 .85 3 .75 1 .61 4 .17 5 .79 • 11 .50 19 .82 3 .57 1 .61 3 .99 5 .60 /2 .00 18 .78 3 .38 1 .61 3 .81 5 .42 12 .50 17 .75 3 .20 1 .61 3 .62 .-5 .23 13 .00 16 .72 3 .01 1 .61 3 .44 5 .05 13 .50 15 .69 2 .82 1 .61 3 .25 4 .87 14 .00 14 .65 2 .64 1 .61 3 .07 4.68 14 .50 13 .62 2 .45 1 .61 2 .88 4 .50 15 .00 12 .59 2 .27 1 .61 2 .70 4 .31 15 .50 11 .55 2 .08 1 .61 2 .52 4 .13 16 .00 10 .52 1 .89 1 .61 2 .33 3 .94 16 .50 9 .49 1 .71 1 .61 2 .15 3 .76 17 .00 8 .46 1 .52 1 .61 1 .96 3 .58 17 .50 7 .42 1 .34 1.61 1 .78 3 .39 18 .00 6 .39 1 .15 1 .61 1 .59 3 .21 18 .50 5 .36 0 .96 1 .61 1 .41 3 .02 19 .00 4 .32 0 .78 1 .61 1 .23 2 .84 19 .50 3 .29 0 .59 1 .61 1 .04 2 .65 20 .00 2 .26 0 .41 1 .61 0 .86 2 .47 20 .50 1 .22 0 .22 1 .61 0 .67 2 .29 21 .00 0 .19 0 .03 1 .61 0 .49 2 .10 21.50 1 .61 0 .33 1 .95 22 .00 1 .61 0 .24 1 .85 22 .50 1 .61 0 .16 1 .77 23 .00 1 .61 0 .08 1 .69 23 .50 1 .61 0 .01 1 .62 á s e r% M I M I
II I I I I I i ff / W u • I N I M r 0 1 1 1 I m a I I I I % NKR 1 • • • - INSTITUTEof HYDROLOGY
The Ins titute of Hydrology is a compone nt establishme nt of the UK Natur al Environm ent Rese arch Co uncil, grant-aided from Gove rnment by the De partment of Ed ucation and Scie nc e . For ove r 20 yea rs the Institute has be en at the fore front of research e xploration of hyd rological syste ms within comple te catchme nt areas and into the physical proce sse s by which rain or snow is transforme d into flow in rivers. Applied studies , und e rtak e n both in the UK and ove rse as, e nsur es tha t rese arch ac tivities are close ly re lated to practical ne eds and that newly de velope d me thod s and instrume nts are tested for a wide range of environme ntal conditions The Institute , bas e d at Wallingford, employs 140 staff, some 100 of whom are gradua tes. Staff struc ture is multidisciplinary involving physicists, geographe rs, geologists, compute r scientists , mathe maticians, chemists, e nvironme ntal sc ientists, soil sc ientists and botanists Research de pa rtments include catchm ent rese arch, re mote se ns ing, instrume ntation, data proce ssing, mathe matica l mode lling, hyd roge ology, hyd roc hemistry soil hydrolog y, evaporation flux studies, vege tation -atmosp he ric inte ractions, flood and low-flow pre dictions , catchment res p onse and enginee ring hyd rology The budg e t of the Institute comp rises £4 5 million pe r year About 50 perce nt re lates to research programmes funded direc tly by the Natura l Environme nt Research Co uncil. Extensive commiss ione d rese arch is also can ie d out on be half of gove rnme nt de pa rtme nts (both UK and ove rseas ), various inte rnational age ncies , environme ntal orga nisations and private sec tor clie nts. The Institute is also resp onsible for nationally archive d hyd rologica l data and for pub lishing annually HYDROLOGICAL DATA: UNITED KINGDOM. •
• Il l ESNI TATESI BI OL OG ICA L ASSOCI ATI ON The Fen Row s Far San e Amb le .. .de Cumbn a LA 22 GU Tel 09662 1466 Fax 6814 Telex 88606 11 ONEONI G MI 16 in oo The Bi n , l a be re leay Fast Stoke Ware ham Dors et 15435 183 Tel M N 462314 Fax 462180 Telex 18505110 NEO NE AEI 16174001 • D18T I1V IT OF ETD RO LOGT Walli ng ford Oxon OT IO BBB Tei 0491 314800 Fax 12286 Telex 549365 Mv ol l a es Offi ce Staylatle Llanb r r aw , Powy s. ST 19 7DB Tel 05515 652 IN STIT UTE or TERAE I TIUA L ECO LOG Y • Egbabem k Resear c h Re tie s & Leh Row e Penc e* Mallot hen ER26 00 6 Tel 031 445 4343 Fax 3943 Telex 72579 Paac k en Reeea rc k A t k a Thll of k W h .. ., Giassel Barc hor y t r ia l di nes/me Al l 435 Tat 13302 3434 Fax 1303 Telex 7393% M e: low ed Rees si c• Grange over Sa tt h Cent ral LA I STU Tel 04464 2264 Fax 42115 Telex 65102 • M eal s Woe/ Exp er im al al Stati on Ab bot. Rupton It ar tmgdoe Car obs PE II 21 Tel 04673 361 Fax 467 Telex 12416 I lasep s Reeea fet Saabs Reri v oa Roe] t ango Cerr e ck l i.. .5-7 -14 Tei 3246 36400: h ut 1553E5 Telex 6:224 r t n • l weelt ' Wen zel l ea s Wei eherr. Don e, N O D SAS Te. RaTS 51.31.5 F. 5 lai T • DEM M E Or VI ROLO GY Mansfi eld Road Oxfor d OS : • Tel 0965 512361 F. 59662 Telex 53147 I • UN IT Or COM P A RATI VE PL ATT ECO LO GY Dept of Plant Scie nce' Sae/held Uruver ssy Shethe id S 21 2TR1 Tel 0742 76E655 Fes 760104 Telex 5472 5 • UNI T Or WATER 1113 0 0110 3 n r ro ss Dep t ol Ci vil Emanat ing New casu s I/r un n er? • Newc astle p er. Tyre NE: TRU Tei 091 232 851: Fax 36 2 Cd l l eie x 53654 • DI RECT OR AT E OE TEAREI TIII AL TREERIVAT ER SCI ENCES Natur al E r e110 111WIIII I Research Counc i Polans How e Noa h Mal Avenue Swindon 51142 Tel 0783 40601 Fax 5 11117 Telex 444293 s
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