Travel-Time Discharge Measurements in Netherlands

Henk Cox and Anne Wijtzes, of the Rijksinstituut voor Kust en Zee (RIKZ) in the Netherlands, have recently completed an extensive comparison test of the Argonaut-SL with a travel time system installed at the Spijkenisse Bridge (shown here) near Rotterdam.

The RIKZ was interested in evaluating the Argonaut-SL as a potential replacement for the travel time systems typically used for these measurements, at least in part because of the lower costs associated with installation and maintenance of the Argonaut-SL. A preliminary cost analysis done by the RIKZ shows that, when installation and maintenance are included, a site equipped with an Argonaut-SL is about one-third the cost of a site fitted with a travel time system.

The RIKZ generally recommends a stage-velocity calculation for discharge monitoring, with the discharge calculated as:

Q=kvA(h)

where v is the velocity and A(h) is the wetted surface area (which is a function of water level). The constant k accounts for variations from site to site and for deviations of v from the vertically-averaged velocity.

Two tests were carried out at the Spijkenisse Bridge, a site near Rotterdam harbor already equipped with a travel time system. As shown in the drawing below, the Argonaut-SL was located on the "backside" of the bridge piling for maximum protection.

Location of the Argonaut-SL
on a piling of the Spijkenisse Bridge.

The following graph shows the results from the second test (the first test results were similar). In both tests, the relationship between the velocities measured by each instrument was quite linear. While there was no reason to expect the relationship between the measured velocities to be perfectly one-to-one, in both tests, regression analyses show that a one-to-one relationship is very nearly the case.

Test results comparing the Argonaut-SL
with an installed travel time system

The overall result of this test is that the RIKZ is confident that the Argonaut-SL is a suitable substitute for travel time systems in any location similar to this test site.

• Argonaut-SL