WSP11706

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications-Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1980
• Title: Development of Procedures to Evaluate Salinity Management Strategies in Irrigation Return Flows
• Water Supply Pro - Doc Type: Report/Study

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processes. The representation of the hydrol-
ogy component varies substantially depending
upon the watershed studied and the desired
application. The state-of-the-art of
modeling soil-water systems is found in the
models outlined in Table 3.3 and described by
Oster and Rhoades (1975),

The hydrologic and chemical components
are normally modeled separately but inte-
gratedly, Huber et a1. (1976) describe
the Basin Simulation and Assessment Model
(BSAM), a generalized hydrologic model that
can be applied to any watershed and also
can be coupled to a suitable salinity 8ub-
model. As classified in Figure 3.1, the
complexity of solute flow models ranges from
simple applications of plate theory assuming
piston-flow movement of solute and water
(Tanji et a1. 1967), to detailed models
which attempt to represent the complex
chemical reactions within the soil profile by
use of both hydrodynamic dispersion and
diffusion principles.

Models integrating solute transport with
soil-water chemistry were initially pursued
by Tanji et a1. (1967), Thomas et a1. (1971),
Dutt et a1. (1972), and Narasimhan (1975).
Descriptions of specific characteristics of
some more recent and more refined models are
outlined in Table 3.4.

Models attempting to also integrate
groundwater flow came even later. The first
models (Konikov and Bredehoeft 1974) cons id-
ered reactions within the water but not
chemical reactions between the water and the
aquifer. As a result, they did not rigor-
ously define the relation of groundwater
salinity to overlying soil salinity. Helweg
and Labadie (1976) computed groundwater
salinity (represented by rDS) by meanS of a
regression equation using the electrical
conductivity (EC) of the soil water and
groundwater. Outlined in Table 3.5 are the
general characteristics of these groundwater
s al i ni ty mode Is.

Assumptions in
Salinity Modeling

Solute flow processes

Review of the models presented in Tables
3.2, 3.3, 3.4 and 3.5 indicated that solute
flow is generally modeled from a few basic
relationships. The principle of conservation
of mass was generally used, and steady state
condi t ions were commonly assumed. The only
exception is the model of Wi11ardson et a1.
(1979), which assumed transit state condi-
tions in modeling the water and solu~e flows.

Solute Flow MJdels of
Soil-Water System.

I

ChromatOgraJhic MJdels
(Plate Theory)
- Dutt (1962)
- Tanji (1967)

Discontinuous Plate MOdelsl/
Vander MOden (1956)

Continuous Plate MOdels 2/
Gardner & Brooks (1957)

I
Diffusion MOdels
(Miscible Displacement Theory)
Bresler & Hanks (1969)
Biggar & Nielsen (1962)

I
Soil-Ion Interaction3/
Systems
Rhoades (1975)
Shaffer (1977)
Dutt (1972)
Narasman (1975)
Thomas (1971)

I
Nousoil-Ion Interaction4/
MJdels
Terkeltaub (1971)
Hill (1973)

Note: 1. Solution remains in an affective plate of colunn 1.IDtil equilibrium with solid phase is obtained.
2, Based on rate theory and ionic equilibrium.
3. Equilibrium concentration of constitutent ions, ion pairs and cation exchange considered.
4. No chemical reactions are considered.

21

Figure 3.1. Development categories of selected solute flow models of the soil-water system.