Average bank height for each advance

vessel delay, etc.) was 1.6 ft/min. This value was based on the dredge's total

advance distance (taken from the daily dredge report due to incomplete dredge

time-series data from 5 and 6 June) of 1,715 ft during 18 hr 17 min. The average

advance rate of Beachbuilder at Reach 2 was 2.9 ft/min based on an advance

distance (calculated from the dredge time-series data) of 22,271 ft over 128.5 hr.

The average advance rate during the entire demonstration was 2.1 ft/min

(23,984 ft of advance over 192 hr). This rate compares fairly well with the

average advance rate of 2.4 ft/min in the final daily dredge log calculated from

manually entered values.

Average bank height for each advance

Advance rates are based on bank height, type of material, current, and winch

uptake so as not to plug the pump. Assuming a constant relative density of sand

in the dredging prisms (and that the dustpan was in new work material when it

was clogged by clay), the advance rate is primarily determined by bank height.

An estimated approximate bank height is also included for each advance in

Table 5. These heights were estimated by personnel on the dredge during demon-

stration and by review of hydrographic surveys, but the dynamic, complex shoal-

ing nature of HOP and the inability to accurately measure an average height for

an entire advance make these very rough estimates. The bank heights dredged

during the demonstration ranged from 2 ft to 20 ft with the higher face predomi-

nantly on the RDB side of the channel (see Figure 8). As expected, when some of

the thicker faces were being dredged, the slower advance rates were encountered,

but with the inaccuracies inherent in estimating average bank height with the

methods used, this relationship was not constant throughout the demonstration

with the heights estimated in Table 5.

Total production and production rate for each advance

Calculation of the total production and average production rate of each

advance was based on the calculated cubic-yards-per-hour parameter in the time

series provided by the contractor. Data collection problems were experienced at

the beginning of the demonstration that precluded dredge data from being

recorded until 6 June at 1140. This lapse in data collection covered a pumping

time duration of 5 hr 31 min when comparing the (time-series) calculated

dredging time to the values reported on the daily dredge report and Form 4267.

The cubic-yards-per-hour parameter value, recorded every 10 sec, was multiplied

by the sampling interval (10 sec) to determine the volume (in cubic yards per

hour) dredged for that time interval. By this method, the total production for the

entire demonstration was approximately 265,000 cu yd. It was decided that the

dynamic shoaling nature at HOP would reduce the accuracy of production num-

bers derived from the channel hydrographic surveys; therefore, the measured

volume of material placed in the marsh was used as the most correct volume. The

original gross volume in the final Form 4267 reported was 248,500 cu yd, but the

credited volume determined by the placement area surveys was approximately

178,000 cu yd. Assuming a 20 percent loss in fines in runoff, the (placement

area surveyed) volume was adjusted up to a gross volume of approximately

222,000 cu yd. The volume of material dredged during the data collection lapse

Chapter 4

Dredging Operational Characteristics Analyses