Methodology to quantify clogging coefficients for grated inlets. Application to SANT MARTI catchment (Barcelona)

ORIGINAL ARTICLE Me hodology o quan i y clogging coe icien s o g a ed inle s. Applica ion o SANT MARTI ca chmen (Ba celona) M. Gómez 1 | J. Pa és 1 | B. Russo 2 | E. Ma ínez-Goma iz 1 1 Flumen Resea ch Ins i u e, Technical Uni e si y o Ca alonia, Ba celona, Spain 2 G oup o Hyd aulic and En i onmen al Enginee ing, Technical School o La Almunia (EUPLA), Uni e si y o Za agoza, La Almunia de Doña Godina, Za agoza, Spain Co espondence Edua do Ma ínez-Goma iz, Flumen Resea ch Ins i u e, Technical Uni e si y o Ca alonia, Ba celona, Spain. Email: edua do.ma inez@ce aqua.com Wi hin he d ainage sys em o a ci y, he se o inle s is in cha ge o aking he un- o p oduced by local s o ms o he s o mwa e /sewe . In he d ainage sys em design he selec ion o app op ia e inle models and hei loca ion is one o he un- damen al aspec s. The hyd aulics o hese inle s has ecei ed g ea a en ion wi hin he las yea s; howe e , ew inle make s p o ide he hyd aulic capaci y o hei p oduc s. In addi ion, hese da a usually conside clean wa e , while in eali y, nume ous inle s can be ei he o ally o pa ially clogged. This aspec should be kep in mind wi hin he design p ocess. In his pape , a me hodology o conside he hyd aulic e ec s o clogging phenomena is p esen ed. The wo k s a ed om a isual inspec ion o he g a ed inle s h oughou he u ban ca chmen o San Ma í, Ba celona, as a means o iden i ying clogging pa e ns, hei epe i i e o ms and hei associa ed equency. A e ha , clogged pa e ns we e ep oduced in labo a- o y es ing o ypical inle s ypes, he eby ob aining he eal quan i y o wa e ha could be cap u ed by each o hem. I was shown ha he same exp ession employed o desc ibe he e iciency o clean inle s can be used o assess he e i- ciency o hose clogged. A educ ion ac o in e ms o hyd aulic capaci y and ela ed o each clogging pa e n has been de ined o use in hyd aulic s udies o uno along s ee s. Finally, he pape compa es he ob ained esul s in e ms o clogging coe icien wi h ano he expe imen al campaign ca ied ou in o he ca ch- men o he ci y. KEYWORDS ca chmen , clogging, inle , su ace wa e 1|INTRODUCTION S ee s cons i u e a su ace hyd aulic ne wo k du ing ain e en s when uno lows along he s ee s. Flow on he s ee s in a ainy day depends on se e al ac o s like ain all in ensi y, u ban a ea, slopes, s ee c oss-sec ions, and inally he ype and numbe o inle s. S ee s ha e an impo an ole associa ed o s o mwa e managemen and any s ee mus ensu e sa e y o pedes ians (Gómez, Macchione, & Russo, 2011; Ma ínez, Gómez, & Russo, 2016; Russo e al., 2013a) and ehicula a ic acco ding o a le el o se ice associa ed o a e u n pe iod (Ma ínez, Gómez, Russo, & Djo dje íc, 2017, 2018). D ainage sys em can be seen as composed by wo sub- sys ems: he unde g ound wi h s o mwa e /sewe sec ions and he su ace one, o med by s ee s. This concep o dual d ainage sys em is he bes desc ip ion o wha eally occu s du ing a ain e en . Bu hese wo sub-sys ems a e no inde- penden . They a e connec ed by he so-called inle s sys em composed by all he inle s, g a es, gullies, e c. placed in he ci y aiming o cap u e he uno . A he same ime, in case o p essu e s o mwa e /sewe low, hey beha e as a elie al e, by allowing he excess o wa e no accep ed by he s o mwa e /sewe condui o eme ge o he s ee le el. Hun- d eds o housands o inle s a e esponsible o link bo h sys- ems whose p ima y unc ion is o ake he uno o he Recei ed: 29 Ma ch 2018 Re ised: 4 May 2018 Accep ed: 28 June 2018 DOI: 10.1111/j 3.12479 © 2018 The Cha e ed Ins i u ion o Wa e and En i onmen al Managemen (CIWEM) and John Wiley & Sons L d J Flood Risk Managemen . 2019;12:e12479. wileyonlinelib a y.com/jou nal/j 3 1o 10 h ps://doi.o g/10.1111/j 3.12479 s o mwa e /sewe s up o he igh place [A ina e al., 2001; Colo ado Depa men o T anspo a ion (CDOT), 2000] and onwa d o ea men . Nowadays, a la ge a ie y o inle s and g a es exis in he ma ke , di e en om coun ies and e en om ci ies, whe e local adap a ion o s ee s design and me eo ological condi ions has p oduced such di e en shapes, dimensions and, as a consequence, di e en models. Many imes, aes- he ic concep s in luence inle design as in many o he dis- ciplines, hough un o una ely se e al ci ies decide he inle selec ion pu ing i s hese “new”c i e ia wi h no conside a ion o hei hyd aulic capaci y o he p oblems associa ed o hei no mal ope a ion wi h clogging. Mo e- o e , in se e al coun ies i is possible o ind ha mos o local supplie s p o ide no da a conce ning he hyd aulic e iciency o hei p oduc s. Al hough se e al p ocedu es like HEC-22 p o ide in o ma ion abou how o assess he wa e collec ed, hey a e es ic ed o some inle shapes ha a e no ound all o e he wo ld (B own, S ein, & Wa ne , 1996). Recen s udies p opose some p ocedu es o cha ac e ise inle hyd aulic pe o mance. Mos o imes hey a e based on eal-scale expe imen al analysis and, as a esul , allow he es ima ion o cap u ed low depending on s ee geom- e y, inle ype, and gu e low condi ions [Cla k Coun y Regional Flood Con ol Dis ic (CCRFCD), 1999; Gómez & Russo, 2011; Russo e al., 2013b]. In hese s ud- ies, labo a o y es s a e usually done in bes condi ions (i.e., clean wa e , inle wi h no clogged a ea, no obs acles, e c.) so, he ob ained esul s exp essed in e ms o inle hyd aulic e iciency can be conside ed as an uppe limi ha can be un ealis ic in case o inle clogging. In ac , in eal condi ions, dus , di , lea es, o deb is, can educe he a ea o g a ed inle holes, he eby educing he amoun o wa e o be cap u ed. In o de o ake in o accoun he clogging phenomenon, Guo (2006) p oposed he concep o clogging coe icien , which educes he hyd aulic e i- ciency wi h a ac o be ween 0 and 1 (Guo, 2006), al hough he p oposed alues we e no ela ed o heo e i- cal o expe imen al s udies. Clogging phenomenon depends on inle design, ype and densi y o ege a ion, ain all pa e ns, s ee slope, cleaning equency, e c. Al hough he ep oduc ion o he e ec s o his phenome- non is complex, labo a o y and ield s udies could allow a easonable es ima ion o he po en ial educ ion in e ms o hyd aulic e iciency due o clogging. So inle s es ing unde a ious clogging condi ions should be equi ed, being cha ac e isa ion o clogging beha iou and i s se e i y an impo an p e- equisi e o a co ec design o su ace d ainage sys ems. Howe e , i migh be wonde ed whe he inding a cha ac e is ic way o he inle o be clogged is possible. In p e ious s udies, Gómez, Hidalgo, and Russo (2013) in oduced his idea h ough he “clogging pa e n”concep whe e, depending on he ype o inle , some cha ac e is ic o ms whe e holes a e co e ed by lea es, deb is, e c. we e obse ed. The s udy was de eloped in an u ban ca chmen o Ba celona (Rie a Blanca) including s eep and la slopes. Howe e , one doub could appea : a e hose clogging pa e ns ep esen a i e o he whole ci y? In o de o answe his ques ion, he au ho s o his wo k selec ed ano he ca chmen in Ba celona wi h di e en cha ac e is ics, close o he beaches, la slopes, and po en ially mo e p one o be a ec ed by clogging, and maybe o de elop di e en pa e ns. As s a ed be o e, clogging e ec s a e speci ic o local clima e condi ions, land use, s ee geome y, and inle models. The me hodology de eloped could be applied wi h no loss o gene ali y anywhe e hough. In his wo k, he ol- lowing ea u es we e conside ed: •Field isi s in d y and we wea he condi ions, o obse e h oughou he ca chmen be o e and a e ain e en s he way inle s become clogged. •Compa ison o he clogged inle s o iden i y common aspec s in o de o de ine clogging pa e ns, and assess he equency associa ed o each one. •Quan i ica ion o he educ ion o hyd aulic capaci y associa ed o each one o he clogging pa e ns, h ough expe imen al s udies ca ied ou in he hyd aulic labo a- o y o he Technical Uni e si y o Ca alonia ( ollowing UPC labo a o y). •P oposal o clogging coe icien s a he end o he p o- cess, o be used o each pa e n, and make i ex ensi e o o he case s udies. 2|STORMWATER CAPTURED BY INLETS An excess o wa e o e he pa emen can gene a e sa e y p oblems o pedes ians and ehicles. Some imes i is esponsible o acciden s due o aquaplaning (i.e., loss o adhe ence be ween i es and pa emen ) and loss o s abili y o pedes ians and ehicles. Many ci ies ha e ini ia ed s ud- ies o ien ed o quan i y he s ee hyd aulics and p ocedu es o de e mine bes loca ion o inle s. Hyd aulic capaci y o a single inle depends on di e en pa ame e s: s ee geome y, s ee low, and ype o inle (Gómez & Russo, 2011; Russo e al., 2013b). The low cap- u ed by an inle could be high o low in gene al, al hough i depends essen ially on he compa ison wi h he s ee low. Absolu e low cap u ed by he inle some imes is no enough o ha e a clea idea o he hyd aulic pe o mance o an inle . Tha is why he concep o hyd aulic e iciency (E)is de ined as he a io be ween he cap u ed low (Q c ) o e he low along he s ee and app oaching he inle (Q). This pa ame e p o ides mo e objec i e in o ma ion abou he pe o mance o a single inle espec o he s ee low. E i- ciency (E) anges om 0 o 1 and i is a dimensionless pa ame e . 2o 10 GÓMEZ ET AL. E=Qc Qð1Þ As p e iously s a ed, es s o achie ing inle hyd aulic e iciency a e usually conduc ed unde he bes condi ions wi h clea wa e and no deb is. Reali y wi hin a ci y is no like his, no ma e he e o s om he municipal cleaning se ices. Al hough in ense s ee washing and sweeping is ca ied ou , a ce ain laye o dus and o he deb is-like lea es om ees will be buil up. Du ing a ain e en , he u ban uno , he mos e ec i e cleaning p ocess in a ci y, sweeps away mos o hese deb is and once he inle is eached wa e en e s in o he s o mwa e /sewe and deb is co e s pa ially o o ally he inle . Tha is why in he u ban s ee design, a kind o secu i y coe icien educing he e i- ciency should be conside ed. In o de o assess he coe icien s o a ec he hyd aulic e iciency o he inle s, a ield s udy in an u ban ca chmen o he ci y o Ba celona was de eloped. Visual inspec ions and pic u es o e e y selec ed inle we e collec ed (Figu e 1). A comp ehensi e analysis o he clogged inle s was ca ied ou , by de e mining se e al ypes o clogging pa e ns, hei associa ed equency and hei spa ial dis ibu ion. Once he ield s udy was inished, a quan i ica ion o he e iciency educ ion was de e mined h ough labo a o y es s, and educ ion coe icien s o hyd aulic e iciency we e p oposed. 3|TEST CASE: SANT MARTI CATCHMENT IN BARCELONA The u ban ca chmen in he dis ic o San Ma i in Ba ce- lona, wi h an a ea o 6.49 km 2 was selec ed as es case o implemen he me hodology (Figu e 2). The ca chmen is loca ed in he lowe pa o he ci y, nex o he Medi e a- nean Sea wi h ele a ion om 1 o 18 m. The easons (Pa és, 2014) o selec his ca chmen a e: •Mos o he ca chmen is loca ed on eclaimed land, ini- ially below sea le el. G a els and sand deposi s a e he usual geology in he a ea. Due o his, la mo phology is he no mal p o ile wi h slopes om 0.1 o 5% and an a e age o 0.5%, hus he inle s a e mo e p one o be clogged. Beaches a e close o he a ea so sands ca ied by he wind can be ound all o e he a ea o in e es . •A ailable Geog aphic In o ma ion Sys em (GIS) in o - ma ion including posi ion and ype o e e y inle loca ed in he ca chmen (Figu e 2). This in o ma ion was p o- ided by o me CLABSA, now BCASA, he public company in cha ge o he managemen o he ci y sewe sys em. •The inle sys em is composed by 6,946 inle s, wi h 6,874 inle s ha can be g ouped in 98 di e en models, while 72 a e non-classi ied models. Mo eo e se en models a e enough o desc ibe 80% o all he inle s. Fo all hese easons, San Ma í ca chmen could be seen as an example o he wo s case ega ding inle s clogging, due o i s mo phological clima ic condi ions (Medi e anean clima e cha ac e ised by sho and in ense ain alls). The i s pa o he s udy included he di ec isual inspec ion o e i y he da abase o inle s, acco ding o GIS in o ma ion, classi ied by he Uni e sal T ans e se Me ca o (UTM) coo dina es and inle ype. Acco ding o he exis ing ypes wi hin he da abase, se en models we e selec ed as he mos ep esen a i e ones. These models a e E5, R-121, Impu, Me idiana, Del a/Ba celona, Teide and Onda/Eb o and, as p e iously men ioned, hey ep esen 80% o all he inle s in he ca chmen . In Table 1 inle dis ibu ion o e e y model is shown. F om he 5,539 inle s, a g oup o 1,300 inle s was selec ed. The selec ion c i e ia we e a uni o m spa ial dis i- bu ion o he inle s along he ca chmen and a minimum o 15% o e e y model. One o he objec i es is o check whe he he clogging pa e ns a e uni o mly dis ibu ed along he ca chmen o no . Each o he 1,300 inle s was isually inspec ed, h ee imes as a minimum, and a pic u e o each one was aken o eco d he eal condi ion o he inle . In o de o ake in o accoun he po en ial e ec o soil e osion due o ain all in he clogging phenomenon, wo we ield obse a ions we e planned. These wo isi s we e conduc ed wi hin he days a e a ain e en (1–3 maximum) du ing he ainy season in Ba celona (au umn), while he las hi d isi was ca ied ou unde d y wea he condi ions (in sp ing), wi h a minimum o 2 weeks wi h no ain all, o check i he clogging pa e ns a e modi ied by he ac i i y o he municipal cleaning se ices. FIGURE 1 (a) Clean and (b and c) clogged inle s GÓMEZ ET AL.3o 10 4|CLOGGING PATTERNS A he end o he ieldwo k, an ex ensi e g aphical da a se was pe o med and employed o he analysis o he inle s. Due o he small di e ences, clogging s a es unde d y and we wea he condi ions we e combined o simpli y he app oach. The analysis was unde aken s aigh ly in he PC sc een, no conside ing ye compu e ision p ocesses ha could be employed o accele a e he p ocess. Howe e , he pe cen age o holes co e ed by lea es o deb is (i.e., clogging elemen s) is possible o be dis inguished as a gene al alue. The c i e ia indica ed in he Table 2 we e adop ed. Due o hese c i e ia, speci ic clogging pa e ns FIGURE 2 Gene al iew o he basin and inle s. Inle s a e indica ed wi h do s TABLE 1 Numbe o he selec ed inle models in he ca chmen Inle model To al % o inle s in he basin Inle no. 1: E5 257 3.70 Inle no. 2: R-121 425 6.12 Inle no. 3: IMPU 616 8.87 Inle no. 4: Me idiana 1,162 16.73 Inle no. 5: Del a/Ba celona 2,226 32.05 Inle no. 6: Teide 233 3.35 Inle no. 7: Onda/Eb o 620 8.93 To al 5,539 79.74 To al S . Ma í ca chmen 6,946 100 4o 10 GÓMEZ ET AL. we e de ined depending on he a io be ween he clogged a ea (A c ) and he o al a ea o holes in he inle (A h ). Fo wo di e en inle s o same model and clogged a ea, likely he clogging does no always ha e he same shape. To simpli y he app oach, some clogging shapes ela ed o e e y pa e n ha e been p oposed (i.e., desc ibing he mos gene al manne he inle is clogged), acco ding o he ieldwo k obse a ions. Shapes associa ed o he di e en clogging pa - e ns we e mo e easily ecognised o some inle s (i.e., Eb o, Teide, o IMPU), while o o he inle s (E5 and 4 Me idiana) ew o no clogging p oblems we e obse ed, hus no pa e ns we e p oposed o hose inle s. Clogging pa e n C1 is asso- cia ed o he co e age o na ow spaces, many imes nex o he ex e nal pe ime e o he inle . Some o he inle s show a mo e in ense clogging e ec , in case ha cleaning p ocess is no enough, hus a C2 pa e n is p oposed. Di e ences be ween C1 and C2 pa e ns a e mo e in ense o inle s 3, 5, 6, and 7 (i.e., IMPU, Ba celona, Teide, and Eb o). Finally, i he clogging p ocess p og esses, ano he pa - e n, called C3, can be obse ed, whe e a signi ican a ea o holes is co e ed. I was obse ed ha no all he inle s each C3 pa e n, while inle s 1, 2, and 4 (E5, R-121, and Me idi- ana) a e hen less suscep ible o de elop his pa e n. In Figu e 3 he p oposed shapes o e e y clogging pa e n o he selec ed se en inle models a e p esen ed. The inle s wi h highe suscep ibili y o be clogged a e inle s Eb o, Teide, and IMPU, maybe due ha hey a e old models, placed a ound 30 yea s ago. Inle s E5, Me idiana, and Ba celona ha e been ins alled mo e ecen ly, wi hin he las 5–10 yea s, and show o ha e be e condi ions o a oid clogging e ec s. This di e ence could be explained by poo main enance o inadequa e cleaning o hese g a ed inle s. 5|FREQUENCIES AND DISTRIBUTION OF CLOGGING PARTNERS F equencies and spa ial dis ibu ion o clogging pa e ns we e assessed unde d y and we wea he condi ions. F e- quency dis ibu ion can be conside ed qui e simila o bo h si ua ions, hence he ela ed alues in all cases we e com- bined and only a single equency was p esen ed. The e o e, i was obse ed ha clogging phenomenon occu s h ough- ou he yea in we and ainy season, and i seems ha pa e ns do no depend on empo ali y. Second ele an aspec is ha a e iewing he spa ial dis ibu ion o clogging pa e ns, hose appea all o e he ca chmen . No signi ican di e ences be ween highe o lowe slope a eas we e obse ed, hus i may indica e ha acco ding o he obse ed da a, clogging pa e ns show a qui e uni o m spa ial dis ibu ion h oughou he ca chmen . Those di e ences could be esponsible o he ime needed o mo e om one pa e n o ano he . This aspec has no been e i ied hough. The mo e common pa e ns a e C1 and C2, wi h equen- cies be ween 20 and 70%, while pa e n C3 is less equen , wi h equencies om 2 o 9%. The equency o pa e ns C1 and C2 is app oxima ely he same o all he inle s, excep o inle Eb o, whe e C1 pa e n is mo e usual (75%) han C2 (15%). In addi ion, an in e es ing issue is o compa e he numbe o inle s ha show some clogging p oblem. This could be exp essed by combining he equencies associa ed o C1, C2, and C3 pa e ns. The accumula ed equency (C1 + C2 + C2) is app oxima ely 95% o Eb o, 89% o Teide, 60% o IMPU, 38% o R-121, 10% o Ba celona, and 0% o Me idiana and E5 (Table 3). 6|HYDRAULIC ANALYSIS OF CLEAN AND CLOGGED INLETS So a , a desc ip ion o he clogging p oblems in he Ba ce- lona's ca chmen o San Ma í has been p esen ed. No wi h- s anding, one o he objec i es o his wo k is he quan i ica ion o he educ ion o he hyd aulic e iciency due o clogging p oblems wi hin inle s. In p e ious s udies de eloped a he UPC (Technical Uni e si y o Ca alonia –Ba celonaTech) (Gómez & Russo, 2011; Ma ínez, 2000), i was p oposed ha hyd aulic inle e iciency (E) can be ela ed o he app oach low (Q) and he immedia ely ups eam wa e le el (y) as a po en ial unc- ion as ollows: E=AQ y  −B ð2Þ whe e Eis hyd aulic e iciency o he inle , Qis app oach- ing low o he inle (l/s), yis wa e le el immedia ely ups eam he inle (mm), A and B a e wo speci ic coe i- cien s o e e y inle . This exp ession was p oposed a e conduc ing labo a- o y es s wi h clean wa e and no clogging e ec s. Thus, he issue o be sol ed is whe he his exp ession is s ill alid o clogged inle s, o ano he app oach o o mula is needed o desc ibe he hyd aulic e iciency o a clogged inle . Two inle s o he se en selec ed ones we e es ed in he UPC labo a o y, and i was p o ed ha he same po en ial unc ion p oposed o clean wa e s could be used o clogged inle s, jus modi ying he A and B coe icien s depending on he clogged a ea. TABLE 2 P oposed c i e ia o classi y clogging pa e ns ollowing he ield inspec ion No hing (clean inle ) A c /A h < 10% Pa e n C1 10% ≤A c /A h < 25% Pa e n C2 25% ≤A c /A h < 50% Pa e n C3 50% ≤A c /A h < 80% Inle ou o o de A c /A h ≥80% GÓMEZ ET AL.5o 10 FIGURE 3 Clogging pa e ns o selec ed models 6o 10 GÓMEZ ET AL. The same es p o ocol used o clean wa e condi ions was adop ed (Gómez & Russo, 2011), wi h ci cula ing lows o 25, 50, 100, 150, and 200 L/s, longi udinal slopes o 0, 0.5, 1, 2, 4, 6, 8, and 10% and ans e se slopes o 0, 1, 2, 3, and 4%. Tes s we e de eloped by co e ing wi h gypsum pa o he holes o he inle , ep oducing he pa e n o be s udied, as can be seen in Figu e 4 o Ba celona inle . Expe imen al da a a e p esen ed in Figu e 5, and om he analysis o hese esul s i is possible o conclude ha a po en ial law is good enough o ep esen he hyd aulic capaci y o he clogged inle s. Pa ame e s A and B ha e a ied acco ding o clogged a ea (Table 4), al hough qui e high co ela ion coe icien s we e ob ained o he wo inle s [i.e., 91.5% o Ba celona inle (Pa e n C3), 77.2% o Teide inle (Pa e n C1), and 75.9% o Teide inle (Pa e n C2)]. This con i ms he appli- cabili y o he e i ied po en ial law o clean inle s o clogged inle s oo. 7|COEFFICIENTS A AND B FROM GEOMETRICAL CHARACTERISTICS OF THE INLET Pa ame e s A and B can be de e mined om expe imen al es s as s a ed be o e. Bu in many cases enginee ing depa - men s o local municipali ies ha e no ime o possibili ies o es he g a es hey a e planning o place. Gómez and Russo (2011) p esen ed a p oposal o app oxima e he A and B pa ame e s om he inle geome y, in case he non- es ed g a e has simila dimensions o hose o he es ed inle s. The exp essions o es ima e A and B a e: A=1:988Ag0:403 p0:19 n +1ðÞ 0:088 nl+1ðÞ 0:012 nd+1ðÞ 0:082 ð3:1Þ B=1:346L0:179 W0:394 ð3:2Þ whe e A g is minimum ec angula a ea in he inle including all he holes (m 2 ), p is a io in % be ween he o al a ea o TABLE 3 F equencies associa ed o each one o he obse ed clogging pa e ns Inle model Pa e n C1 (%) Pa e n C2 (%) Pa e n C3 (%) Pa e n C1 + C2 + C3 (%) Ou o o de (%) To al (%) E5 0.00 0.00 0.00 0.00 0.00 0.00 R-121 18.37 17.35 0.00 37.76 3.06 40.82 IMPU 22.37 18.42 9.21 60.53 1.32 61.84 Me idiana 0.00 0.00 0.00 0.00 1.50 1.50 Ba celona 0.00 7.48 2.55 10.04 0.73 10.77 Teide 40.00 49.09 0.00 89.09 0.00 89.09 Eb o 75.54 15.11 4.32 94.97 1.44 96.41 FIGURE 4 Rep oduc ion o C3 clogging pa e n o he Ba celona inle , and iews o he expe imen al se -up FIGURE 5 Ba celona inle . Clean wa e and C3 condi ions TABLE 4 Pa ame e s a, B de e mined a e labo a o y es s Teide Inle clean Pa e n C1 Pa e n C2 Pa e n C3 A 0.425 0.340 0.327 — B 0.714 0.800 0.790 — Ba celona Inle clean Pa e n C1 Pa e n C2 Pa e n C3 A 0.355 ——0.230 B 0.850 ——1.003 GÓMEZ ET AL.7o 10 holes A H and he A g , de ined as p = (A H /A g )100, n is num- be o ans e sal ba s o he inle , n l is numbe o longi udi- nal ba s o he inle , n d is numbe o diagonal ba s o he inle , Lis leng h o he inle (cm), Wis wid h o he inle (cm). These exp essions can be employed o clean inle s, while i was no clea whe he his exp ession is applicable o clogged inle s. Fo he selec ed and es ed clogged inle s, he ele an geome ical in o ma ion ( o al a ea o a ailable holes, numbe o ba s, e c.) was ob ained and A and B alues we e calcula ed wi h exp essions 3.1 and 3.2. These alues we e compa ed wi h he ob ained A and B om he es s, as Table 5 indica es. Values show e y simila esul s, wi h di e ences in he second decimal posi ion. This could indica e ha o non- es ed inle s i is possible o app oxima e he A and B pa am- e e s wi h Equa ions 3.1 and 3.2, and, as a consequence, i is possible o quan i y he educ ion o hyd aulic e iciency on he inle due o he clogging e ec s. Na u ally, he expe i- men al p ocedu e is p e e ed, hough in case o no ha ing he possibili y o ca y ou labo a o y es s, i is possible o calcula e he A and B pa ame e s o clogged inle s o es i- ma e hei hyd aulic e iciency educ ion. 8|PROPOSAL OF CLOGGING COEFFICIENTS As s a ed be o e, use s conside mos o imes a secu i y coe icien , educing hyd aulic e iciency o he inle , in o de o conside he clogging e ec s. Howe e , acco ding o mos e e ences, i is usually a ixed alue o 0.5 (Gómez e al., 2013), hus educing e iciency o hal o he alue ound in labo a o y es wi h clean wa e condi ions. In his wo k, i was obse ed ha no all he inle s show he same clogging pa e n, and equencies o occu ence o clogging a e no he same o all ypes o inle s. The e o e, depending on he clogging pa e n, i a educ ion o 50% o hyd aulic e iciency is applied, eal hyd aulic capaci y o he inle could be unde es ima ed o o e es ima ed. I is accep ed ha e iciency educ ion can be exp essed as: Eclogged =1−co ðÞEclean ð4Þ whe e E clogged is e iciency o he clogged inle , E clean is e i- ciency o he clean inle , and c o is clogging coe icien , om 0 o 1 (0 clean inle , 1 o ally co e ed inle ). I exp ession is ew i en by in oducing he ΔEpa ame- e , as he di e ence be ween E clean and E clogged , he clog- ging coe icien co can be exp essed as: ΔE E=Eclean −Eclogged Eclean =c0ð5Þ Ne e heless, as i was p esen ed wi hin he p e ious sec ions, e iciency o clean o clogged inle can be app oxi- ma ed by a po en ial law, as a unc ion o he Q/ypa ame e , wi h a ying alues depending on bo h low condi ions and s ee geome y. I is possible o ep esen he e iciency educ ion as a unc ion o low condi ions Q/y. Figu e 6 shows he e olu ion o c o agains low o he wo es ed inle s, and o each es ed clogging pa e n (i.e., C1, C2, and C3). I is possible o obse e ha clogging coe icien inc eases wi h he low along he s ee , hus i is no con- s an , and alues a e di e en o e e y pa e n. No wi hs anding, he design c i e ia o d ainage sys em a e associa ed o a e u n pe iod conside ed o he design s o m employed o he calcula ions. The e o e, design alues o c o should no be ela ed o low low condi ions, bu o highe alues o Q. On he o he hand, in u ban a eas high haza d condi ions o pedes ian and ehicles a e mainly ela ed o high low eloci ies (and consequen ly medium and low low dep hs y) p oduced by low oughness o impe ious su aces like s ee s and sidewalks and/o hei high slope (Ma ínez e al., 2016, 2017, 2018; Russo e al., 2013a) In his amewo k, i seems jus i ied he adop ion o high a ios Q/y o he design o su ace d ainage sys ems. I he a io Q/y= 10 is conside ed as a e e ence o high haz- a d condi ions, coe icien s o c o a e indica ed in Table 6, o he es ed inle s and associa ed pa e ns. Gómez e al. (2013), as a esul o a e y simila expe i- ence ocused on ano he ca chmen o Ba celona (Rie a TABLE 5 A and B pa ame e s ob ained om expe imen al es s and om inle geome y Pa ame e Inle Teide Inle Ba celona C1 pa e n C2 pa e n C3 pa e n A expe imen al 0.340 0.327 0.230 A om geom 0.365 0.311 0.265 B expe imen al 0.800 0.790 1.003 B om geom 0.777 0.790 1.022 FIGURE 6 E olu ion o clogging coe icien s agains low condi ions o es ed inle s 8o 10 GÓMEZ ET AL. Blanca), p o ided o he alues conce ning clogging coe i- cien o o he ypes o inle s. The de ini ion o he pa e ns o bo h expe iences was he same and, in o de o compa e he esul s ob ained in he wo expe imen al campaigns, he alues p esen ed in Table 7 a e e e ed o he low condi ion Q/y= 10. On he basis o he analysis o he esul s ob ained in hese wo campaigns i is possible o s a e ha , depending on he inle and he clogging pa e n obse ed, alues o c o can be close o he adi ionally used alue o 0.5 o no . Clog- ging coe icien s o pa e n C1 a e close o 0.25–0.50, hence a pe o mance o he collec ing sys em is be e han ha conside ed by mos use s. On he o he hand, o he mos c i ical clogging pa e n (C3), clogging ac o is always highe han 0.5 eaching in some cases alues close o 0.7. On he o he hand, clogging coe icien is no he same o all he inle s. I was obse ed ha some ypes a e mo e p one o be clogged, and o he s show less clogging p oblems. Thus, when clogging coe icien s a e employed wi hin he design o inle s sys ems, he ype o inle and he clogging pa e ns obse ed in he analysed ca chmen mus be conside ed. 9|CONCLUSIONS In his pape , a me hodology o conside he clogging issues o inle s placed along he s ee s has been p oposed. Field- wo k obse a ions in an u ban ca chmen loca ed in he ci y o Ba celona has been also ca ied ou . E e y inle ype shows di e en clogging pa e ns, wi h a di e en equency o occu ence in he ca chmen . Some inle ypes a e mo e p one o be a ec ed by his issue and some o he s a e less a ec ed by clogging. This phenomenon could be ela ed o he ime he inle s ha e been placed on he s ee s. Inle s wi h mo e clogging p oblems, Eb o, IMPU, and Teide we e placed 30 yea s ago, and inle s wi h ewe p oblems like E5, Me idiana, and Ba celona ha e been placed wi hin las 5–10 yea s. This di e ence could be explained by poo main enance o inadequa e cleaning o he g a ed inle s. Clogging pa e ns ha e been ound all o e he ca ch- men , p esen ing a uni o m spa ial dis ibu ion. The slope o he s ee was no ound o in luence he clogging pa e n; howe e , i could accele a e he clogging e ec and he ans e om one pa e n o ano he . This aspec should be add essed in u u e s udies. Acco ding o he obse a ions, clogging pa e ns and e- quency o occu ence we e simila be o e and a e ain e en s, unde d y and we wea he condi ions. In his case, his can be due o he e o s o municipal cleaning se ices. Reduc ion o inle e iciency is obse ed and he hyd au- lic cha ac e isa ion o a clogged inle can be unde aken by employing he same po en ial law p oposed o clean inle s. A consequence o his ac is ha speci ic pa ame e s o his o mula (i.e., A and B pa ame e s) a y o he clogged inle espec o he alues o clean inle s. Pa ame e s can be ob ained om labo a o y es s o can be app oxima ed acco ding o he geome y o he clogged inle , by conside - ing he same exp essions employed o clean inle s bu applying i o he clogged geome y (i.e., conside ing he e ec i e hole a ea) o he inle s su e ing clogging phenomena. The clogging coe icien usually conside ed as 0.5 uni- o mly all o e he ca chmen , can a y depending on he ype o inle , and he clogging pa e n obse ed. The alues o clogging coe icien s ob ained in his wo k ha e been compa ed o o he alues ob ained du ing ano he expe i- men al campaign ca ied ou in ano he ca chmen o Ba ce- lona (Rie a Blanca). The esul s o bo h s udies show ha clogging coe icien c o can be in he ange o 0.23 o 0.50 o he mos usual clogging pa e ns, while o he wo s case, clogging ac o should be close o 0.7. In any case, e e y inle o e e y pa e n will ha e di e - en c o and hese alues should be employed o desc ibe much be e he eali y o he collec ing sys em wi hin an u ban a ea. ACKNOWLEDGEMENTS The au ho s acknowledge he coope a ion o he company in cha ge o he sewe sys em managemen in Ba celona du ing he pe iod o he ield s udy, CLABSA, as well as he coop- e a ion o BCASA, public company now in cha ge o Ba ce- lona's sewe ne wo k. ORCID E. Ma ínez-Goma iz h ps://o cid.o g/0000-0002-0189-0725 REFERENCES A ina, S., Calenda, G., Calomino, F., Cao, C., La Loggia, G., Modica, C., … Vel i, P. (2001). Sis emi di ogna u e, Manuale di p oge azione. Milano, I aly: Hoepli. B own, S. A.,S ein, S. M. & Wa ne , J. C. (1996). U ban d ainage design man- ual (Hyd aulic Enginee ing Ci cula No. 22). Washing on, DC: Fede al Highway Adminis a ion, US Depa men o T anspo a ion. Cla k Coun y Regional Flood Con ol Dis ic (CCRFCD). (1999). Hyd ologic c i e ia and d ainage design manual. Las Vegas, NV: Cla k Coun y Regional Flood Con ol Dis ic . TABLE 6 Clogging coe icien s o es ed inle s conside ing Q/y=10 C o =ΔE/EPa e n C1 Pa e n C2 Pa e n C3 Teide 0.234 0.360 — Ba celona ——0.545 TABLE 7 Clogging coe icien s o es ed inle s conside ing Q/y = 10 C o =ΔE/EPa e n C1 Pa e n C2 Pa e n C3 IMPU 0.451 0.502 0.674 EBRO 0.265 0.400 0.667 GÓMEZ ET AL.9o 10