Figure 1. Visualization of 1 m3 of dredged material

ERDC TN-DOER-I2

July 2000

Hopper volume.

Vessel (hopper) weight.

So, to evaluate the TDS method, how well each of these data parameters can be measured needs to

be determined. With the exception of hopper volume, each of these parameters is established in

dredging practice and is part of the Corps' standard dredge reporting. In addition to determining

TDS accuracy and repeatability, it is also important to compare its relative accuracy and repeatability

to those of hydrographic surveys.

Important requirements associated with TDS are quality assurance (having methods to check the

results), repeatability, and minimization of the labor and expense of obtaining, analyzing, and

reporting the data. The technology to implement a TDS pay system is available, and the Corps is

increasing its understanding of TDS.

TDS Theory. The following derivation of the TDS

equation is based on Rullens (1993). Dredged ma-

terial consists of both water and solid particles as

illustrated in Figure 1, but the concept of TDS can

be viewed as just the total mass of the dredged

material minus that of the included water. Assume

that Figure 1 contains 1 m3 of dredged material with

the solid particles surrounded by the water matrix.

If the percentage of volume occupied by the solid

particles is defined as the variable P, then the total Figure 1. Visualization of 1 m3 of dredged

mass of particles in the unit volume can be calculated

material

by multiplying P times the specific density of the

particles ρs. The remaining percentage of volume in the 1 m3 is occupied by water and can be

determined as 1 - P. The mass of this water then equals (1 - P) times the density of the water ρw,

kg/m3.

The total mass of the 1 m3 of dredged material then equals

Pρs + 1 - P ρw

(1)

So, with the value of the average density of the dredged material in the hopper ρh, kg/m3, determined

by this indirect measurement methodology

ρh = Pρs + 1 - P ρw

(2)

ρ - ρw

P= h

(3)

ρs - ρw