Sediment Transport Modeling at the Oued Fodda Watershed Level Using HEC-RAS 1D Software

GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 SEDIMENT TRANSPORT MODELING AT THE OUED FODDA WATERSHED LEVEL USING HEC-RAS 1D SOFTWARE Souhila BENKACI , Boualem REMINI Blida 1 Uni e si y, Facul y o Technology, Depa men o Wa e Science and En i onmen , 9000 Blida, Alge ia E-mail: ssbenkaci7[email p o ec ed], eminib@yahoo. ABSTRACT The objec i e o he cu en wo k is o de e mine he amoun o sedimen s anspo ed ups eam and a he le el o Oued Fodda dam. The la e is conside ed one o he i s la ge dams buil in Alge ia. I ’s exposed o a se ious sil a ion p oblem ha educes i s capaci y e e y yea . The simula ion was execu ed using he HEC-RAS so wa e, o he pe iod a ied om Janua y 01, 2016 o Ap il 30, 2016. The modeled sec ion consis ed o abou 9999 m leng h, subdi ided in o 141 i e s a ions dis an om each o he by 70 m. The obse a ion o he s udied i e sec ion bed- p o ile was selec ed as a c i e ion o compa ing he esul s o he model wi h he eal alues obse ed. A oughness coe icien o 0.031 was used. A quan i a i e es ima e wi h a de e mina ion coe icien , R2, o 0.92 was used o suppo he alidi y. The mass and concen a ion o sedimen s inc eased signi ican ly in he c oss- sec ions loca ed a he dam ups eam. A o al cumula i e mass was es ima ed a app oxima ely 712699 ons, jus ups eam o he dyke, and a maximum concen a ion o 22.35 g/l was obse ed, pa icula ly o h ee main sec ions selec ed ups eam o he Fodda wadi. Howe e , a he ese oi le el, he concen a ion a iabili y is obse ed du ing lood pe iods, i.e., only o he mos impo an lows. Keywo ds: GIS; HEC-RAS; Oued Fodda dam; Sedimen anspo ; Sil a ion. 1 INTRODUCTION Due o i s impo ance, he anspo o solid ma e ials is a majo p oblem in he Magh eb coun ies [1]. In Alge ian i e s, his p oblem has always a isen in an acu e way. Due o he lack o da a, i s assessmen emains complex. The eno mous quan i ies o sedimen s anspo ed a e a he o igin o he p og essi e educ ion o he ese oi s s o age capaci y. In ac , a ound 65 million cubic me e s o sil is deposi ed annually in Alge ian dams [2]. The a ious ba hyme ic su eys e ec ed du ing he pe iod (1986–2008) by he Na ional Agency o Dams and T ans e s (ANBT) on all 59 dams in exploi a ion e ealed ha he olume los h ough sil ing was 898 mm³, i.e. 13.4% o he o al ese oi s olume [3–4]. Nume ous me hods o es ima ing solid anspo exis in he li e a u e, including models ha explo e physical laws such he S . Venan equa ion o he liquid phase, and he anspo equa ions o he solid phase [5]. Al hough hey ai h ully ep esen anspo phenomena, hese models equi e he in oduc ion o a la ge numbe o pa ame e s. Ma hema ical models ha e been de eloped using h ee app oaches: empi ical models, which ela e he low o sedimen o he ou all, he a ious clima ic and biophysical explana o y a iables [5]. I s majo disad an age is he di icul y o i s calib a ion o la ge basins [6]. Reg essi e models ( low-TSS) deduced om he a io, be ween he obse ed low, he alues o he suspended solids concen a ion (Le ki , 2009), and he concep ual models, which conside e osion dynamics. These models ha e he ad an age o es ima ing lows o di e en ime s eps, bu hey equi e a ela i ely long calib a ion pe iod, and peaks in TSS concen a ion which a e gene ally unde es ima ed [7]. Resea ches has in ensi ied and expanded o es ablish new me hods: 1D models, nume ous 2D models and inally 3D models, which ha e been de eloped o simula e sedimen anspo p ocesses [8]. In iew o his, ou wo k is 161 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 a pa o a one-dimensional solid ma e ial anspo modeling using he HEC-RAS so wa e. This code was c ea ed by he U.S. A my Co ps o Enginee s and has been employed by se e al enginee ing i ms and go e nmen al o ganiza ions [9]. I calcula es he sedimen anspo capaci y associa ed wi h each c oss-sec ion as a con ol olume o all g ain sizes [10]. The Wadi Fodda sub-wa e shed was selec ed o his s udy. This basin is exposed o a majo p oblem o soil deg ada ion, which accele a es he sil ing phenomenon a he le el o he Wadi Fodda dam. The la e is conside ed one o he i s la ge dams buil in Alge ia. I ’s in ended o he i iga ion o he Middle Cheli pe ime e [11]. I s s o age capaci y has dec eased conside ably o e he las 18 yea s. The sil a ion a e has been es ima ed a abou 54.29% and he ba hyme ic condi ion o he ese oi has become e y wo ying [12]. 2 STUDY AREA The Uppe and Middle Cheli wa e shed is loca ed in he wes o he Fodda Wadi basin, which is co e ing a su ace a ea o 1153.5 km2. The la ge Cheli wa e shed, which is in he no hwes e n Alge ia, is mos ly occupied by he la e and loca ed in i s no heas e n po ion (Fig. 1). Figu e 1. Oued Fodda wa e shed The Oued Fodda sub-basin has a conside able elie , an elonga ed shape (Fig. 2), and a highes poin can each 1950,7 m [13]. Wi h 282 empo a y wadis and 81 pe manen wadis o aling oughly 1053.45 km and 897.16 km, espec i ely, i ea u es a complex hyd og aphic ne wo k. I is mos ly d ained o e a 92.14 km leng h by he Oued Rouina [11]. Ou s udy a ea is exposed o a se ious p oblem o soil deg ada ion. Gully e osion has been iden i ied owa ds he ups eam o he basin [14] (Fig. 3). This is a he o igin o an impo an p oduc ion o sedimen , which accele a es he sil ing p ocess a he le el o he Wadi Fodda dam ese oi (Figs. 4 and 5). I collec s an annual olume o sil o 3.2 million m3 [15]. An annual loss o i s s o age capaci y has been es ima ed o be abou 4,248 km3, i.e. a sil ing a e o 45.43% in 2015 [13]. 162 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 Figu e 2. Hypsome ic Oued Fodda wa e shed map Figu e 5. Vase deposi ups eam o he Oued Fodda dam (Pho o: Benkaci, Augus 2017) Figu e 3. Gully o ma ion a he Oued Fodda wa e shed Figu e 4. Oued Fodda dam ese oi iew wi h an ini ial capaci y o 228 Mm3 (Pho o: Remini, 2008) 163 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 The physiog aphic cha ac e is ics o he Oued Fodda sub-wa e shed we e calcula ed based on A cGisTM so wa e [16] and summa ized in Table 1 below: Table 1. Physiog aphic cha ac e is ics o he Oued Fodda sub-basin Cha ac e is ics Value Obse a ion A ea (km2) 1153.5 - Compac ness index Kc 1.74 he basin is elonga ed a o ing slow low o uno Max. Al i ude (m) 1950.7 Highes poin o he basin A e age Al i ude (m) 709.40 - Median Al i ude (m) 750 Rep esen s 50% o he o al su ace a ea o he basin Minimal Al i ude (m) 142 Wa e shed ou all Equi alen ec angle leng h (km) 93.144 - Equi alen ec angle wid h (km) 12.384 - Mean slope index Imoy (%) 1.72 - Global slope Index Ig 0.1 S ong elie D ainage densi y Ds (m) 328.16 - 3 MATERIALS AND METHODS A he Wadi Fodda dam ese oi , he HEC-RAS p og am was p ima ily used o model he anspo o sedimen . I enables o all g ain sizes and a con ol olume calcula ion o he anspo capaci y associa ed wi h each c oss- sec ion (Fig.6). The Exne equa ion, also known as he mass conse a ion and he sedimen con inui y equa ion, p o ides he ounda ion o i s basic idea [10]: (1−𝜆𝑝)𝐵 𝜕𝜂 𝜕𝑡 =−𝜕𝑄𝑠 𝜕𝑥 (1) whe e: 𝜆𝑝 po osi y o ac i e laye , B channel wid h [m], 𝜂 channel ele a ion [m], 𝑄𝑠 sedimen load anspo ed [m3/s], X dis ance [m], T ime [s]. Figu e 6. Con ol olume used in HEC-RAS sedimen calcula ions [17] 164 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 3.1 Model inpu pa ame e s The calcula ion o sedimen anspo ups eam and a he Fodda Wadi Dam equi es h ee inpu da a iles, as shown in Fig. 7. Figu e 7. Me hodological diag am o he inpu pa ame e s in he HEC-RAS model The Manning’s coe icien is he mos impo an pa ame e o be adjus ed in he calib a ion o he HEC-RAS model. The use o a single Manning’s coe icien may no be su icien and adequa e o ep esen he ue oughness o a i e unde di e en low condi ions [18]. Due o assump ions in he da a o he model limi a ions, no model will gi e indings ha a e exac ly in line wi h he eal esul s. Bu i is necessa y o achie e a easonable co ela ion be ween obse ed alues and model ou comes [10]. Fo ou model, he adjus men o he Manning coe icien is pe o med ollowing he hyd aulic simula ion o he uns able low o e a pe iod om Janua y 01, 2016 un il Ap il 30, 2016. The wa e su ace ele a ions (WSEl) associa ed wi h he measu ed low a es and he ou pu low a es es ima ed by he HEC RAS so wa e a e compa ed as pa o he calib a ion p ocedu e. The alues o he obse ed (measu ed) liquid lows a e based on he daily liquid lows ob ained a he le el o he Oued Fodda dam di ec ion du ing he conside ed pe iod. Se e al oughness alues we e es ed: 0.030, 0.031, 0.032, 0.033, 0.034 and 0.035. The Manning alue e ained ( o which he e o is minimal) is equal o 0.031 [13]. 3.1.1 Geome ic Da a The geome y o he s udied sec ion was ini ially c ea ed in A cGisTM using a o m o digi al geog aphic ec o da a “TIN” (Fig. 8) ex ac ed om he SRTM Wo ldwide Ele a ion Da a (3 a c second Resolu ion 90 m) o he Oued Fodda wa e shed (Fig. 9). These da a a e hen expo ed using he HEC-GeoRas so wa e and isualized h ough he “Geome ic Da a” window (Fig. 10) wi h he HEC-RAS so wa e [13]. The modeled sec ion was app oxima ely 9999 m in leng h ، subdi ided in o 141 i e s a ions o app oxima ely 70 m pe pa . Sec ion 69 is loca ed downs eam (immedia ely ups eam o he Wadi Fodda dam) a a dis ance o abou 50 m (Fig. 11). On he o he hand, sec ion 9945 is loca ed ups eam. I is he e o e, conside ed as he i s sec ion o he ups eam Oued Fodda. Model inpu pa ame e s Geome ic Da a - Image Shu le Rada Topog aphy Mission (SRTM) T iangula ed i egula ne wo k (TIN) Flow Da a Daily liquid low a es Mean slope Sedimen Da a Ini ial condi ions and anspo pa ame e s Bed g ada ion Sedimen bounda y condi ions 165 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 Figu e 8. T iangula ed i egula ne wo k (Tin) o he Oued Fodda wa e shed Figu e 9. Shu le Rada Topog aphy Mission image, SRTM Wo ldwide Ele a ion Da a (3 a c second Resolu ion) o he Oued Fodda wa e shed 166 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 Figu e 10. Geome ical da a window isualized h ough a Google Ea h image Figu e 11. Cha ac e is ics o he ups eam c oss-sec ion (69) o he Oued Fodda Dam dike 167 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 3.1.2 Flow da a and bounda y condi ion The simula ion o sedimen anspo begins wi h he c ea ion o a quasi-uns able low ile. Two bounda y condi ions a e conside ed (Fig. 12). • The i s is selec ed a he i s c oss sec ion o he Fodda wadi (sec ion 9945). Fo his condi ion, he da a o he daily liquid lows obse ed a he dam ups eam ha e been in oduced wi h a ime s ep o 12 days conside ing he du a ion o he simula ion, which uns om Janua y 1, 2016 o Ap il 30, 2016. • The second bounda y condi ion is loca ed a he downs eam (wadi Fodda dam dike). I simply co esponds o he alue o he a e age slope (0.0242) a he le el o he c oss-sec ion conside ed (sec ion 69). Figu e 12. HEC-RAS window o he quasi-uns able low bounda y condi ions The ob ained low hyd og aph (Fig. 13) illus a es he occu ence o wo majo loods in Ma ch 2016. The i s is obse ed on Ma ch 12, co esponding o a low a e o abou 27 m3/s, and he second is obse ed on Ma ch 20 wi h an es ima ed low a e o 20.66 m3/s. Figu e 13. Flow hyd og aph 168 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 3.1.3 Sedimen s da a The sedimen da a ile is based on h ee main inpu quan i ies. These a e illus a ed in Fig. 14. Figu e 14. Me hodological diag am o he sedimen da a ile 3.1.3.1 Bed g ada ion The "bed g ada ion" da a ile is based on he esul s o he G anulome ic analysis (Table 2). Samples we e collec ed om se e al segmen s along Wadi Fodda, jus a he dam ups eam. The g anulome ic analysis sample was e ec ed a he Na ional Labo a o y o Habi a and Cons uc ion (LNHC) o Oued Sama (Algie s). The cu e is ep esen ed in Fig. 15. Figu e 15. G ading cu e o he sample aken along he ups eam sec ion o he Oued Fodda dam Sedimen Da a Ini ial condi ions and T anspo pa ame e s T anspo Func ions Bed e olu ion Func ions Sedimen a y Sedimen a ion a e Bed G ada ion G anulome ic Analysis Sedimen bounda y condi ions Ra ing cu e Solid Flow 175 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 Figu e 24. Tempo al concen a ion a iabili y a he ups eam sec ions o he Fodda Wadi Dam Figu e 25. Tempo al concen a ion a iabili y a he Wadi Fodda Dam 176 GeoScience Enginee ing Vol. 69 (2023), No. 2 geoscience.cz pp. 160–178, ISSN 1802-5420 DOI 10.35180/gse-2023-0097 The spa ial a ia ion p o ile o he sedimen concen a ion can be displayed o du a ion o simula ion. A e y signi ican a ia ion is obse ed a he ups eam c oss-sec ions o he Fodda wadi and also a he sec ions om he downs eam. An example is illus a ed (Fig. 26) conside ing he wo loods: 23 Janua y and 2 Feb ua y 2016. The maximum alue o he sedimen concen a ion was es ima ed a ound 6736.267 mg/l o he Janua y 23 d lood and 12278.532 mg/l o he Feb ua y 2nd lood. Figu e 26. Spa ial sedimen concen a ion a iabili y (Example o : 23 Janua y and 02 Feb ua y 2016 loods) 5 CONCLUSION HEC RAS so wa e was used o model solid anspo a he Fodda Wadi dam ese oi . Once all o he pa ame e s we e se o wi hin hei use ul anges, he model wo ked as expec ed. The obse a ion o he bed p o ile was chosen as a s anda d o con as ing he ou pu o he model wi h he ac ual alues ha we e obse ed. Also he R2, which is equal o 0,92, is he coe icien o de e mina ion ha suppo ed he alida ion. This demons a es s ong conco dance be ween model p edic ions and ac ual da a. We can he e o e accep ou model as sui able o simula ing sedimen a y anspo in one dimension. The ba hyme ic le ees a Alge ian ese oi s a e a ely pe o med. The employed me hod is especially use ul o wa e sheds missing ba hyme ic da a o wi hou hyd ome ic s a ions ups eam o dams. ACKNOWLEDGEMENT I would like o add ess a g ea hanks o he Algie s di ec ion o dams and ans e s (ANBT), o he chie o exploi a ion and all he s a o he Oued Fodda dam, who acili a ed my access o he Oued Fodda dam and who pu a my disposal all he necessa y echnical and ope a ing da a, and who accompanied me pa icula ly, o he eco e y o he samples o sil a he le el o he dam and a he le el o he wadis loca ed ups eam. 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