Tidal Barrage Basin Siltation

Barrage Operation

Sluice gate opening 55%

Tidal range (spring↔neap) 7.0 m

Suspended sediment load 220 mg/L

Time acceleration 40 yr/min

Live Readouts

Tidal prism / cycle

– Mm³

Gate flow speed

0.00 m/s

Siltation rate

0.0 mm/yr

Bed risen

0.0 cm

Mudflat exposed

– %

Elapsed time

0.0 yr

How it works

A barrage impounds a basin behind a wall of sluice gates. The sea outside oscillates with the dominant lunar tidal constituent; the basin level lags behind it, filling and draining only through the open fraction of the gates:

h_sea(t)  = (R/2) sin(2π t / T_M2),  T_M2 = 12.42 h
dh_basin/dt = k · opening · (h_sea − h_basin)   (linear reservoir / orifice-lag model)
Tidal prism  P = A_basin · (h_basin,max − h_basin,min)   [per cycle]

The exchange flow through the gates drives a current whose speed is proportional to |dh_basin/dt|. Suspended sediment settles out of slack, low-velocity water and resists resuspension in faster water (a simplified Krone/Partheniades erosion–deposition law):

dz_bed/dt =  +k_dep · C · max(0, 1 − v/v_crit)    (deposition when flow is slow)
           −k_ero · C · max(0, v/v_crit − 1.6)  (mild scour only in strong flushing flows)

As the bed rises it eats into the basin's live storage, which shrinks the tidal prism further — a self-reinforcing siltation trend documented at real impounded estuaries. The exposed mudflat area at low tide is read off the basin's bowl-shaped hypsometry using the current low-tide level relative to the accreted bed. Opening the gates wider raises exchange velocity and can flush sediment back out; closing them for steady head (better for turbine output) accelerates silting — a real trade-off tidal-barrage operators balance.

Open water Exposed mudflat Suspended sediment

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