Long‐term evolution and morphodynamic equilibrium of tidal channels

Abstract

[1 ] This contr ibution inves tigates the morp hodynam ic equil ibrium of funnel -shape d well-mixe d estua ries and/or tida l channel s. The one-di mensional d e Saint Venant and Exner equations are solve d numerical ly for the ideal case of a fric tionally domi nated estua ry consisti ng of noncoh esive sedim ent and with insignif icant interti dal storage of wat er in tida l flats and salt mars hes. This class of estuaries turns out to be invariabl y flood dominated . The resul ting asym metries in surfa ce elevat ions and tidal curren ts lead to a ne t sediment flux within a tida l cycle which is directed landw ard. As a consequ ence, sedim ents are trapp ed within the estua ry and the bott om profi le evolve s asym ptotical ly toward an equil ibrium confi guration, allo wing a vanishing net sedim ent flux everyw here and, in accordan ce with fiel d observ atio ns, a nearly const ant value of the maxi mum flood /ebb speed. Such an equil ibrium bed profi le is characteri zed by a concavi ty increasing as the estua ry co nvergence incre ases and by a unique ly deter mined value of the depth at the inlet section. The final length of the estua ry is fixed by the longi tudinal extens ion of the very shallow area which tends to form in the landw ard portion of the estuary. Note that sediment advect ion is neglec ted in the analys is, an a ssumption appropriat e to the case of not too fine sediment .I NDEX TERMS: 4235

Morphological evolution of the Dee Estuary, Eastern Irish Sea, UK: A tidal asymmetry approach

“…This may then cause basin infilling. Under ebb-dominant conditions, the opposite is true and net seaward transport will occur (Lanzoni and Seminara, 2002), causing sediment export from the estuary. The suspended load fraction of sediment transport is affected to a greater extent by tidal asymmetry than is the bedload fraction (Dronkers, 1986).…”

“…Dronkers 1986;1998). Incidentally, an estuary with an equilibrium configuration may still retain a degree of tidal asymmetry (Lanzoni and Seminara, 2002). Morphological stability is the ability of an estuary to return to its original state after a disturbance (Hume and Herdendorf, 1993).…”

“…Also, although tidal propagation is widely accepted as the major bathymetric forcing mechanism in estuaries, recent theory suggests that it is the bathymetry that controls the sediment regime, and not the reverse as previously thought (Prandle et al, 2006). In either case, undoubtedly morphodynamics and hydrodynamics are tightly coupled in longterm evolutionary processes (Lanzoni and Seminara, 2002).…”

Sistema interconectado de canales de marea del estuario de Bahía Blanca, Argentina: evaluación de la circulación de sedimento como carga de fondo por métodos acústicos

“…Así, estudios de campo (Gardner & Bohn, 1980;Steel & Pye, 1997) e interpretación de modelos conceptuales y numéricos (Fagherazzi & Furbish, 2001;Fagherazzi & Sun, 2004;D'Alpaos et al, 2005) han permitido predecir la morfodinámica asociada a ellos. En general, la literatura existente trata sobre la hidrodinámica que interviene en los canales de diferentes magnitudes formados en ambientes estuariales (Savenije, 2001;Fagheratzzi et al, 2003;Lawrence et al, 2004), sobre la consecuencia de las corrientes y asimetrías de la marea en la dinámica de los sedimentos y otras característi-cas morfológicas de los mismos (Schuttelaars & de Swart, 2000;Lanzoni & Seminara, 2002), como así también sobre el análisis morfométrico de canales pequeños (Marani et al, 2003;Di Silvio & Dal Monte, 2003).…”

Depth‐integrated modeling of suspended sediment transport

“…Note that the parameters d j ( j = 1, 3) are typically small for slowly varying flows like tidal flows [Lanzoni and Seminara, 2002] and flood waves. In particular, d 3 is usually much smaller than d 1 and d 2 , and therefore the second term in square brackets in (26) can be neglected.…”