Hydrodynamic Investigation and Numerical Simulation of Intermittent and Ephemeral Flows in Semi-Arid Regions: Wadi Mekerra, Algeria
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J. Hydrol. Hydromech., 60, 2012, 2, 125–142 DOI: 10.2478/v10098-012-0011-6 HYDRODYNAMIC INVESTIGATION AND NUMERICAL SIMULATION OF INTERMITTENT AND EPHEMERAL FLOWS IN SEMI-ARID REGIONS: WADI MEKERRA, ALGERIA KHALED KORICHI1,2), ABDELKRIM HAZZAB1) 1)Laboratory of Modeling and Computational Methods, University of Saida, BP 138 Ennasr Saïda 20002, Algeria; Mailto: [email protected] 2)Faculty of Engineering, Department of Civil Engineering, University of Djillali Liabes, Sidi Bel Abbes, BP 89, Sidi Bel Abbes 22000, Algeria. Semi-arid regions are characterized by important infrequent rainfall. They often occur in early autumn and give rise to devastating floods. Flooding problems at Wadi Mekerra, located in the Sidi Bel Abbes town (Northwest Algeria), was traditionally the main concern of researchers and government officials. In this work, the magnitude of raging flood wave in the studied catchment and the principal causes are discussed. After this, we present the main hydromorphometric features and the results of numerical simulations of flood wave. This simulation is done by using finite volume shock capturing schemes. It concerns applying the first order Godunov scheme and the second order Monotonic Central scheme. The Manning roughness coefficient was used as a calibration parameter. The comparison of numerical results with observed data confirms more stability and accuracy of applied numerical schemes in rising limb phase than in the falling limb phase. These results provide information on flood forecasting and monitoring of changes in the magni- tude of the flow in Wadi Mekerra. KEY WORDS: Semi-arid, Temporary Flows, Wadi Mekerra, Flood Wave, Saint-Venant Equations, Finite Volume, Shock Capturing. Khaled Korichi, Abdelkrim Hazzab: HYDRODYNAMICKÝ VÝSKUM A NUMERICKÁ SIMULÁCIA OBČASNÝCH A KRÁTKODOBÝCH PRIETOKOV V SEMIARIDNÝCH OBLASTIACH: WADI MEKERRA, ALŽÍR. J. Hydrol. Hydromech., 60, 2012, 2; 114 lit., 13 obr., 7 tab. Semiaridné oblasti sú charakterizované významnými občasnými dažďami. Vyskytujú sa spravidla v jese- ni a spôsobujú devastačné povodne. Povodne vo Wadi Mekerra v meste Sidi Bel Abbes (severozápadné Alžírsko) sú často problémom pre výskumníkov a vládnych úradníkov. Práca analyzuje devastačné povodne v tomto povodí. Okrem toho sa uvádzajú najdôležitejšie hydromorfomertrické charakteristiky a výsledky simulácií povodňovej vlny. Simulácia je aplikáciou Godunovovej schémy prvého rádu a Monotonickej cen- trálnej schémy druhého rádu. Ako kalibračný parameter bol použitý Manningov súčiniteľ drsnosti. Po- rovnanie simulovaných a pozorovaných údajov potvrdzuje väčšiu stabilitu a presnosť počas rastúcej vetvy prietokovej vlny, ako je tomu v klesajúcej fáze. Tieto výsledky sú informáciou o možnostiach predpovede a monitoringu povodní vo Wadi Mekerra. KĽÚČOVÉ SLOVÁ: semi-aridný, občasné povodne, Wadi Mekerra, povodňová vlna, rovnice Saint- Venanta, konečný objem, pohltenie nárazu. Introduction damage (Hansson et al., 2008 ; Jonkman et al., 2008). Almost all natural phenomena can produce disas- The inundations risk is considered as the product ters; however flooding is the most important in of the occurrence probability of floods and conse- terms of lost materials and human lives (Mudd, quences associated with these events (Raaijmakers 2006; Huang et al., 2010). Prediction and control of et al., 2008). By possessing a diagram of the situa- damage caused by these disasters require special tion, it would be possible not only to manage risk, identification of vulnerable areas and determination take the most appropriate steps to eliminate loss in of factors amplifying the magnitude of generated life and minimize property loss, but also have di- 125 K. Korichi, A. Hazzab verse opportunities to provide the appropriate di- 2007; Chaponnière et al., 2007; (Pilgrim et al., mensioning of hydraulic structures (Breton and 1988; Hughes, 1995; Sharma and Murthy, 1998; Marche, 2001). Wheater et al., 2006). Other approaches propose the The estimated impact of floods and the risk as- coupling of hydrological, hydraulic models and sessment that follows are issues for which the liter- statistical analysis. This is especially the combina- ature provides different analysis approaches tion of surface and groundwater hydrology (Rozos (Gregory et al., 1993; Haase et al., 2003 ; Olfert et et al., 2004; Bouri et al., 2007; Kingumbi et al., Schanze, 2008). The used tools for the floods 2007), or between the stochastic and dynamic ap- treatment are flow modelling, analysis of flood proaches (Hreiche et al., 2007; Lajili-Ghezal, frequency and evaluation of potential annual cost of 2007). damage (Boyle et al., 1998). Recent works have been performed to calibrate Semi-arid regions are characterized by infrequent and validate various models for Wadis whose flow rainfall but sometimes very important (Colombani regime is intermittent or even ephemeral (cf. Tab. et al., 1984 ; Pedro et al., 2006). These cloudbursts 1). One cites innovative studies distributed in such often give rise to flooding whose consequences are semi-arid zones. It is about of hydrological model sometimes unforeseen (Hansson et al., 2008). developed for Australian drylands (Costelloe et al., However, streams in semi arid areas are character- 2005), or hydro-biological model for the same type ized by irregular flow and a strong hydrologic fluc- of zone in Brazil (Pedro et al., (2006). in the Mid- tuation (Arab et al., 2004). During the year, inter- dle East, Alexandrov et al., (2007) quantify the mittent flows dominate in most Wadis (Argyroudi sediment transport in the Negev watershed. Modern et al., 2009). A mismatch between lotic and lentic techniques involve the use of Digital Elevation conditions, is thus noticed (Morais et al., 2004). Models (DEM) for flood forecasting by parameter- It should be noted that this type of region where izing algorithms for two-dimensional hydrodynam- most rivers are ephemeral, do not have, to date a ic flood simulation (Sanders, 2007). global treatment approach. This is justified by In Algeria, we can refer to the studies of many reasons. (a) The lack of data that represents a Dechemi et al., (1994) in the Tafna watershed and handicap to study of changes in hydrological bal- the works of Achit and Ouillon (2007) for the Wadi ance (Sivapalan et al., 2003). (b) The occasional Abd. change of climate and anthropic conditions, which By tracking all these methods, numerical model- leads to an imbalance in the hydrologic fluxes and ling of transient and complexes free surface flows physical characteristics of the basin (Puigde- can be explored as an interesting approach. Horritt fabregas and Mendizabal, 1998; Xoplaki et al., and Bates (2002) present an example of a two- 2004; López-Moreno et al., 2007). (c) The high dimensional numerical model of flood wave propa- variability of ephemeral events and the hydrology gation. Mathematically, floods waves can be gov- of dryland zones. This implies a strong nonlinearity erned by the Saint-Venant model which is a nonlin- of explored models (Nouh, 2006; Hreiche et al., ear hyperbolic system of partial differential equa- 2007; Kingumbi et al., 2007; Lajili-Ghezal, 2007; tions. Nonlinear problems represent shock and rare- McIntyre et al., 2007; Nasri, 2007). (d) Spatial het- faction waves. To overcome the handicap in the erogeneity generates a gradual change in the hy- treatment of non-linearity, several solving strategies draulic capacity. So flood risks are confirmed (Leb- have been developed (Liggett and Cunge, 1975; di et al., 2006). Cunge et al., 1980; Guinot, 2010). Historical hydrology (Barriendos and Rodrigo, Among all numerical approaches, the shock cap- 2006; Brázdil and Kundzewicz, 2006) represents the turing finite volume methods have several ad- best tool that can respond to treatment of these is- vantages, since they combine between the simplici- sues. The effort is focused on the methodology. ty of the finite difference method and the flexibility Thus, robust methods are designed to ensure a of the finite element method (Godunov, 1959; Lax compromise between the applicability and accura- and Wenderoff, 1960; Van Leer, 1977; Leveque, cy, especially in rainfall-runoff modelling field, 2004 and Toro, 2006). which represents a major preoccupation in arid and However, in the treatment of real problems (eg: semi-arid catchments (Camarasa and Tilford, 2002; channel with complex geometry), some schemes Benkaci and Dechemi, 2004; Nasri et al., 2004; still need to overcome numerous difficulties (Wang Cudennec et al., 2005; Hreiche et al., 2007; Moussa et al., 2000). For instance, the treatment of the et al., 2007; McIntyre et al., 2007; Ouachani et al., 126 Hydrodynamic investigation and numerical simulation T a b l e 1. Targeted papers relevant to flood wave in Wadis and rivers. Reference River basin or region Type Main contribution Cherif et al. (2009) Wadi Mekerra, Algeria Ephemeral Statistical Study Dechemi et al. (1994) Tafna Wadi, Algeria Intermittent Statistical study Horritt and Bates Severn river, UK – 2D Numerical model (2002) Nasri et al. (2004) El Gouazine and Dekekira, Tuni- Intermittent Flood impact sia Costelloe et al. (2005) Lake Eyre, Australia Both Hydrological models Pedro et al. (2006) Taperoá, Brasil Intermittent Hydro-biological model Alexandrov et al. (2007) Eshtemoa, Negev Ephemeral Sediment tranport Achit and Ouillon Wadi Adb, Algeria Intermittent Sediment transport (2007) Bracken et al. (2008) Nogalte and, Torrealvilla, Spain Both Rainfall and flood Sanders (2007) Santa Clara River –