PRODUCTION CALCULATIONS (cont.)

ERDC TN-DOER-I5

August 2000

ρw

= the density of the water

V = the flow velocity in the pipe

A = the area of the dredge pipe

The solids flow rate in the dredge pipe is defined as:

a f a Af

ρs - ρw

Mt =

ρm V

(2)

ρm - ρw

with ρm the sediment mineral density. The load in a dredge hopper can be defined in terms of

volume of in situ materials or weight of sediments in the hopper. The volume of in situ material is

computed by the following expression:

ρ - ρw

VOL = h

(3)

VOLh

ρi - ρw

with the solids load in a dredge hopper computed by:

b gb

ρh - ρw

ρm VOLh

(4)

ρm - ρw

with VOLh the hopper volume and ρh the average density of the material in the hopper, calculated

by dividing the weight of the material in the hopper as measured by the draft sensors located in the

hull of the vessel, by the volume of material in the hopper as measured by the water level sensors

mounted above the hopper.

The data reduction equations for the in-line production meter contain a total of six variables; the

density of the water (ρw), the sediment mineral density (ρm), the in situ density of the sediments

(ρi), the velocity as measured by the flow meter (V), the slurry density measured by the nuclear

density gauge (ρs), and the pipe diameter (D).

The data reduction equations for the hopper production monitoring system contain a total of five

variables; the density of the water (ρw), the sediment mineral density (ρm), the in situ density of the

sediments (ρi), and the average density of the material in the hopper, ρh. As mentioned before, this

average density measurement is calculated by the weight of the material in the hopper (Wh) divided

by the volume of the material in the hopper (VOLh).

Each of the previously mentioned variables have some error associated with their values. This error

may be associated with changing physical conditions in the dredging environment such as water

temperature and salinity levels and variations in the mineral and organic content of the sediments,

or measurement error inherent in the instrumentation. The error contributed by each variable will

propagate through the production equations into the final production calculation.