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Title: Mayport-Mill Cove model study. Report 3, Mill Cove study : hydraulic model investigation
Authors: United States. Army. Corps of Engineers. Jacksonville District.
Brogdon, Noble J.
Parman, Joseph W.
Keywords: Fixed-bed models
Hydraulic models
Mayport-Mill Cove
Mill Cove
Jacksonville, Florida
Publisher: Hydraulics Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-79-12 rept.3.
Description: Technical Report
Abstract: A fixed-bed model of Mayport-Mill Cove constructed to scales of 1:500 horizontally and 1:50 vertically, reproduced a portion of the Atlantic Ocean adjacent to the entrance and the St. Johns River upstream to Hibernia Point. The purpose of the model study was twofold: (a) to investigate the effects of proposed improvement plans for the Mayport Naval Basin area on existing shoaling rates, hydraulics, salinities, and flushing; and (b) to investigate the effects of proposed improvement plans in the Mill Cove area on flushing, hydraulics, salinities and channel shoaling. The model study was conducted in three phases: phase 1 involved the model verification tests; phase 2 involved the Mayport Naval Basin Study; and phase 3 involved the Mill Cove Study. Phase 3 is reported herein; phases 1 and 2 are reported in Reports 1 and 2 of this series. The model verification tests described in Report 1 indicated that the model hydraulic and salinity regimes were in satisfactory agreement with those of the prototype for comparable conditions. Model verification also included a comprehensive shoaling verification of shoaling rates and patterns in the navigation channel and Mayport Naval Basin. During the shoaling verification, model operation procedures were developed by trial and error to achieve satisfactory reproduction of observed prototype shoaling distribution patterns within the various reaches of the navigation channel and in Mayport Basin. This report contains the results of tests conducted for phase 3 of the study. Based on visual observations and analysis of surface current pattern photographs conducted for 20 proposed plans, 3 plans (15, 18 and 20) were selected for further, more extensive testing. Each of the three plans involved an enlarged weir opening 1,300 ft wide by 12 ft deep at msl and the relocation of approximately 1,400 ft from the west end of the disposal island located off Reddie Point to the east end of the disposal island. Plan 15 included the above weir and disposal island changes in addition to the construction of a triangular-shaped island inside Mill Cove. Plan 18 involved only the above weir and disposal island changes . Plan 20 included the above weir and disposal island changes in addition to an enlargement of Quarantine Island into Mill Cove. Each of the three plans resulted in minimum effects to tide levels in Mill Cove or in the immediate surrounding area. The greatest effect on tides was the rate of filling and emptying of Mill Cove. Effects of the three plans on maximum current velocities in the navigation channel were minimal. Maximum currents, both in the ebb and flood direction, were increased slightly downstream from the weir opening and upstream from Reddie Point for each plan . Maximum currents in the reach of the river parallel to Mill Cove were decreased slightly with each plan. Each plan increased the extent of crosscurrents in the navigation channel near the Mill Cove weir opening; however, navigation through this area should be no problem. Maximum currents throughout the cove in both the flood and ebb direction were considerably higher than those observed during base tests. Each plan resulted in average maximum current velocities through the cove generally about twice the magnitude of those observed during base tests. Maximum currents associated with plan 15 (triangular-shaped island inside cove) would be in the range that would tend to cause scour problems in the area between the proposed island and Quarantine Island. Thereby requiring bank and bottom protection to prevent development of adverse scour. Each of the three plans tested extensively resulted in slack periods and ebb and flood phases generally more in agreement with those observed in the adjacent navigation channel. Surface current pattern photographs showed that each plan caused a marked improvement in flushing of the cove. General ly, each plan is similar in the middle and western end of the cove. In the extreme southeast area, an area having the poorest circulation, plan 15 appears to improve flushing in a larger percentage of the area best of the three plans. Plan 20 is slightly better than plan 18. Each plan resulted in increases in salinity levels in Mill Cove. Plan 18 increases were the greatest, with plan 15 next. Plan 20 increased average salinities the least of the three plans, and was more uniform throughout the cove. Maximum salinity increases occurred in the central portion of the cove; changes became progressively less near the weir and extreme western end of the cove. Generally, each of the three plans resulted in very similar and minimum effects on dye concentrations along the navigation channel resulting from dye released in Mill Cove and at Mathews Bridge. In general, however, concentrations for plan 18 were less than base conditions while those for plan 15 and 20 were higher than base conditions. Plan 20 indicated a slightly better flushing ability than either plan 15 or 18, particularly in the extreme eastern end of the cove. Minimum changes to overall shoaling rates and patterns would result from any of the three plans tested extensively. Effects of each plan were similar and generally within the limits of accuracy in repeating identical tests of this type. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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