River Stage Data

River Stage Data

As previously mentioned, river stage values were manually entered from

readings taken from the MVN river stage board at Pilot Town. Dredging

activities were in the spring of 2002 to coincide with the normal period of high

water on the Mississippi. The stage hydrograph in Figure 6 from MVN's Venice,

LA, Sta 01480 (located at Mississippi River at Mile 10.7 referenced to the

National Geodetic Vertical Datum (NVGD)) shows the river high/low stage

cycles over last 9 years (maximum allowable number of years to plot by the

analysis routine). In Figure 7, the expanded plot of the Venice Station river

stages (from January through July), it can be seen that the highest river stage

attained during the demonstration (3-13 June 2002) was 4.95 ft NGVD. This is

the highest river stage recorded since 20 Jan 1983, when a river stage of 5.15 ft

was measured. While not as high as the record maximum river stage measured at

9.11 ft from a watermark left by the hurricane of 17 Aug 1969, the maximum

river stage measured during the demonstration confirms that the dredge was

indeed tested in high water!

River Current Data

The river surface currents were measured by a FP201 Global Flow Probe,

manufactured by Global Water (Photo 27). The flow probe is an impellor current

meter that measures average water velocity. Due to the limited scope of the cur-

rent meter, all measurements were taken near the surface at a water depth of

approximately 3 ft. The flow probe uses true velocity averaging at a sampling

frequency of 1 Hz to calculate the average velocity over the time interval that the

impellor was in the water, and also measures and records the maximum (or burst)

velocity sampled at 1 Hz. The probe was deployed from the bow of the survey

vessel while tied up alongside the anchor points, and later in the demonstration

off the dustpan gantry at the bow of the Beachbuilder (while stationary) from

various locations in the channel (Photo 28). The impellor was immersed for

approximately one-half minute to measure the average and burst current veloci-

ties. The current measurement positions and velocities are presented in Table 2.

Hydrographic Survey Data

The BD, during dredging, and AD hydrographic surveys of the dredge site

were conducted by MVN and the contractor's survey crews using DGPS and

echo sounders at 200 KHz (as per standard MVN survey specifications). Data

were furnished to the USACE in a structured ASCII format on magnetic media.

Sediment Sample Data

Sediment samples were collected by a drag bucket sampler from the approxi-

mate center of each dredging reach as per MVN specifications. The BD sample 1

from Reach 1 (BD01) was collected 5 June 2003 from the CL Sta 9+00 at -48 ft

Chapter 3

Data Collection Program