TABLE OF CONTENTS In analogy with the 1-D mass balance equation for water, the mass balance equation for dissolved salts states that the sum of the change in salt load over time and the change of the salt fluxes over the distance should be zero, or in case of a source of salts, equal to the source. Hence the cross-sectional averaged salt balance equation reads:
where:
r S is the storage width ratio defined earlier in Chapter 2
F = F(x, t) is the mass flux of salt in kg/s averaged over the cross-sectional area A;
s = s(x, t) is the salinity in kg/m 3.
In contrast to the water balance, Equation 2.2, the salt balance equation does not have a source term. In Equation 5.1, the source term can be disregarded, unless salt is picked up from the bottom or from marginal salt flats. Salt deposition by rainfall is marginal and evaporation does not carry any salt either, so for all practical purposes in alluvial estuaries the source term may be disregarded.
Subsequently, the mass flux is defined as:
where U= U( x, y, z, t) and s = s( x, y, z, t) are the water velocity and salt concentration at a certain point ( y, z) in the cross section. Equation 5.1 can be elaborated by making use of Equation 2.2, the continuity equation of water, into:
where Q is the...
