Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries Report and Symposium Proceedings (1987) / Chapter Skim
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Session D: Dredged Material Disposal Considerations
Session D: Dredged Material Disposal Considerations
Pages 239-276
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From page 239... ...
Roberts SPEAKERS Frank Boerger William K Fehring Willis E
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From page 240... ...
BACKGROUND New federal and state laws and agency regulations have had a significant impact on traditional approaches to dredged material disposal. For example, in the early 1970s the number of authorized open-water disposal sites in the bay area was reduced from 13 to 3: one near Carquinez Strait, one in San Pablo Bay, and one near Alcatraz in the central bay.
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From page 242... ...
Two of the endangered wildlife species that have impacted many projects in the bay area are the salt marsh harvest mouse and the clapper rail, both inhabitants of the inner tidal zone where salt water nourishes pickleweed (Salicornia)
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From page 247... ...
This action has legally and economically restricted ocean dumping as an alternative for other port development and maintenance projects unless a permanent disposal site is designated within a reasonable distance from the coast. As a result, project planning since the mid 1970s has been based almost exclusively on confined upland disposal for both construction and maintenance material -- with the result that no significant new projects have been initiated.
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From page 248... ...
~ 1 ~ cTr\3 ~ ~>.~J ~14 to /\ 1 :f c .~ x~ ,/ t ~ ==N=_11 1 11 11 ll ll 1 ' i:. : I_ I, FIGURE 2 Mafia/Big Bend Project proposed alternative upland disposal areas and existing diked islands.
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From page 249... ...
Project Depth as Projected in the Corps' Feasibility Report (in thousands) , Big Bend Channel Alafia River Channel Cost Items Upland Ocean Upland Ocean Mobilization/ demobilization 1,600 Excavation: Sand 10,540 Rock 1,500 1,600 1,600 20,020 14,580 14,580 10,310 10,310 Land costs860 -- -1,000 Clearing and grubbing100 110 Diking2,030 -- -1,680- Weirs170 -- -170- Mitigation -- -- -- 1,4601,460 Slope protection -- -- -- 3,9002,280 Environmental monitoring110100 120 Total$15,410$21,620$34,930$30,350 Total for upland disposal plans: $50,340 Total for_ocean disposal plans: 351~970 _
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From page 250... ...
In order to contain the 9.5 million yd3 of sand and clay projected to be produced by construction along with future maintenance volumes, a total of 670 acres of disposal area are required, 250 acres for the Alafia River channel and 420 acres for the Big Bend channel. Use of multiple smaller sites significantly increases diking costs and decreases the effici ency of land use.
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From page 251... ...
Thus, this consideration had little impact in the choice of sites. The overall impact of these factors was to limit potential upland disposal sites to a relatively narrow corridor along the western side of the new I-75 roadway.
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From page 252... ...
252 -_~ FIGURE 3 I - 75 corridor .
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From page 253... ...
Since the land use maps generally reflect the most conservative development expectations of area landowners and county officials it is not surprising that when the Corps and the Tampa Port Authority held a public hearing on the Mafia/Big Bend feasibility study, they received intense opposition to the proposed plan. Even now that the initial reaction has passed, county officials continue to tell the authority that it is very doubtful that these areas could be rezoned for use as disposal areas, reflecting continuing and growing political opposition to the plan.
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From page 256... ...
The record shows that over the last decade the amount of ocean-disposed dredged material from sources outside the Mississippi River has steadily decreased to a low of about 20 million yd3. DEVELOPMENT OF THE MULTI-MEDIA APPROACH TO DISPOSAL REGULATION Although in the United States and elsewhere in the 1970s there were serious movements by both private groups and government agencies to ban the disposal of all wastes into the ocean, there has emerged recently a shift of opinion to the belief that ocean disposal of dredged material might create fewer unacceptable adverse impacts than disposal into estuaries.
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From page 258... ...
Application of the Sieve Technique Step One The first step in applying the technique is to establish the acceptable economic limit for transportation of the dredged material. Without exception, in the open ocean distance must extend to waters deep enough to eliminate excessive transport of the disposed material by forces intrinsic to surface waves and currents.
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From page 259... ...
beaches and other important amenities (see Figure 2~. SPONSOR' S ECONOMIC AND NAVI GAT I ONAL COhPAT I B T L I TY PUBL I C ' S SOC I O - ECONOMI C COMPATIBILITY GENERAL OCEANOGRAPHIC COMPATIBILITY ITE SUITABILITY FIGURE 1 General representation of the sieve technique for siting.
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From page 260... ...
1~1-FI8HI - ~ L t` ~, ~.~ ^ ~. FIGURE 2 A plot of sensitive environmental areas that must be protected by buffer zones and screened out by the sieve technique, resulting in Figure 3.
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From page 262... ...
PUBLICtS SOCIO- ECONOMI C COMPATIBILITY GENERAL ~' OCEANOGRAPHI C COMPATIBILITY Wrec' D 9h ~ - - - and auk r zone ~ Fishing Orould SITE SUITABILITY ~Ichderr ~c~ltIO" ~ Toil- ~ our / Fbhlm a ,,lt 1~ / _ MtifkIal / N.t~1 ~ fin SUITABLE SITE LOCATION AND SIZE FIGURE 3 Complete application of the sieve technique to the geographic area shown in Figure 2.
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From page 263... ...
Also, per yard costs associated with these options range widely from a low for unconfined open-water disposal to a high for upland containment or containment islands. Although in general, I am inclined for several important reasons to conclude that ocean disposal is preferable to open-water disposal in estuaries, there are extenuating circumstances associated with geographic location where the latter alternative may be the only feasible approach to managing large quantities of material.
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From page 269... ...
In 1978, based on the provisions of Public Law 95-269, the Corps initiated a major change in the national dredging program to reduce the size of the Corps' fleet to a minimum level required to provide an immediate response to emergency and national defense needs, both in the United States and overseas. Today, the dredging industry performs over 80 percent of the workload, which is about the percentage previously performed with Corps dredges.
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From page 271... ...
In addition, the resultant side slopes of migrating shoal into a navigation channel are often very steep and, on some projects, sidecasting equipment is used to dredge the upper portion of the slope to create a more gentle gradient rather than using the deeper draft hopper dredges. Pneumatic dredges are hydraulic dredges that utilize compressed air rather than centrifugal pumps to supplement the hydrostatic head that exists between the water surface and the bottom of the waterway.
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From page 272... ...
Comparative tests are planned to be conducted during channel maintenance dredging in the Mare Island Strait navigation channel of San Francisco Bay in 1987. The disposal of dredged material is still the most difficult problem in the national dredging program.
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From page 276... ...
276 beneficial uses of dredged material become more widely known, local concerns will focus more and more on assuring that the best use is made of this valuable resource e
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