ACF Dredging: Price the Placement Route and the Return Visit

A nine-foot channel carries a land requirement

Restoring navigation on the Apalachicola-Chattahoochee-Flint system requires space to put the sediment and a plan for the next shoaling event. USACE's August 2026 notice of intent compares dredging with upland-only disposal against a combination of upland and within-bank disposal. Both use a 9,300 cubic feet per second, nine-month flow scenario to establish the nine-foot depth used for estimating dredging quantities [1, section 3].

The September display set gives the placement problem a scale. Its Apalachicola table identifies 2,115,942 cubic yards of initial work, a historical annual dredging sum of 798,967 cubic yards, and 27,786,846 cubic yards in the column labelled for 30 years of disposal. It estimates 926 acres of placement area under an assumption of a 20-foot perimeter dike. These are separate planning quantities: initial excavation, historical maintenance, longer-term storage and land footprint [2, p.6].

Placement capacity has already constrained the work. The published master-manual revisions record reduced Apalachicola dredging since the 1980s because certain reaches lacked adequate disposal capacity [3, p.7-20]. For an upland scheme, land availability governs where a dredge can discharge, how far material must travel and which sites can receive it during each campaign. The estimate needs a reach-to-site allocation with usable capacity, access and the containment works assigned to each destination.

Five reaches dominate the historical annual quantity

The table's largest historical annual quantities occur at reach 13, river miles 75-80, with 132,000 cubic yards; reach 5, miles 39-42, with 105,000; reach 4, miles 35-38, with 98,000; and reaches 11 and 16, each with 84,000. Together they account for 503,000 cubic yards, or approximately 63% of the table's 798,967-cubic-yard historical annual sum. IMWO calculated that share from the five published rows [2, p.6].

Frequency changes the plant decision as much as volume. Reach 5 is recorded as dredged every year, while reach 17, with a 16,000-cubic-yard historical annual quantity, has an interval ranging from one to nine years. One recurring workfront can support a different mobilisation strategy from a small, intermittent shoal. Combining them into one annual average hides the travel, setup and return costs that bidders must recover.

The rows describe the historical maintenance pattern. The master-manual revisions record no Apalachicola dredging since 2001, initially for flow and funding reasons; the August 2026 notice describes ACF maintenance until the 2005 water quality certification denial [1, section 1; 3, p.7-20]. A new programme needs current surveys and a shoaling assessment before using the old quantities to book plant. The September displays also show channel cutoffs, migration and a deeper approach near Wewahitchka, changes that affect where a restored route would actually be maintained [2, p.5].

IMWO original chart and calculation; source: USACE Mobile District September 2026 display set, page 6

Two extra feet have different values on adjoining rivers

USACE reports that previous analysis on the Apalachicola found advanced maintenance, typically an additional two feet of dredging, had not significantly extended the dredging interval. The September design nevertheless includes it at selected difficult reaches as a conservative basis for quantity and disposal-area estimates. On the Chattahoochee, the same display reports a substantial reduction in dredging requirements and cites earlier navigation planning that recorded avoided repeat work at problem areas [2, p.8].

That difference changes the economic test. Additional excavation pays for itself through avoided future work only when the resulting bed survives long enough to avoid or reduce a later campaign. Price the extra excavation, transport and placement against the discounted cost of the return visits it is expected to save. On the Apalachicola, the published finding supports a cautious allowance for that saving. The Chattahoochee history supplies a stronger reason to examine it reach by reach.

The template also separates the nine-foot channel, a further two feet of advanced maintenance and another two feet labelled allowable overdepth. Straight-reach design uses a 100-foot channel bottom, with widening at bends. Keep those excavation components distinct in the quantity model and proposed measurement schedule. Advanced maintenance serves a future shoaling allowance; allowable overdepth defines a separate construction tolerance. Payment for either component will depend on the eventual contract's measurement provisions.

Flow changes the excavation surface and the working window

The proposed flow scenario and the no-action case describe different services. The notice evaluates a nine-foot channel under the 9,300-cubic-feet-per-second, nine-month scenario. Its no-action alternative continues existing water management and a five-month navigation season supporting a seven-foot channel, subject to water availability [1, section 3]. Both remain alternatives in the environmental assessment.

The September flow display relates navigation depth to channel surveys and historical dredging. Its profiles use elevations in NAVD88 and compare water surfaces under several flow cases. USACE identifies the shape and peak of previous high flows, earlier dredging and bank caving as influences on the required flow. Once restored, the channel can be comparatively stable during low-flow periods with little disturbance [2, pp.8-9].

A nine-foot water depth must therefore be translated into a bed elevation along the river under the stated water-surface profile. The estimating survey, hydraulic case and excavation surface need the same reference. Otherwise a change in water level can be mistaken for a change in the amount of sediment to remove.

Programme the work against both channel access and the shoaling season. Mobilising before a major sediment-moving event can leave newly dredged reaches requiring another visit; waiting can compress the available operating period. Compare campaign scenarios using the survey date, expected working flows, move time between reaches, receiving-site readiness and the survey needed to release each completed reach.

Reservoir rules can shorten a nominal five-month season

The published master-manual revisions support navigation in composite conservation-storage Zones 1 and 2. Support stops in Zone 3 or during drought operations and resumes when storage recovers to Zone 1. Extending the season beyond April depends on inflows, climatic conditions, weather forecasts and basin modelling. The manual also provides for navigation bulletins when diminishing flows require vessels to reduce loading or leave the system [3, pp.7-20 to 7-21].

That operating sequence affects a campaign's access and withdrawal plan. Monitor the reservoir-storage forecast alongside local river depth. A temporary rise that improves access can still leave the system below the condition for renewed navigation support. Price the plant's entry, productive shifts and departure against the conditions applicable to that campaign; identify the draft needed by each vessel and the point at which remaining work must be deferred.

The January 2025 operating assessment tested the Stay Agreement's four flow objectives against continued operation under the earlier manual. Table 23 gives the same modelled January-May availability for both alternatives: 2.7% for a nine-foot channel and 42% for a seven-foot channel. Its navigation comparison uses the stated Blountstown flow thresholds of 20,600 and 16,200 cubic feet per second respectively [4, pp.43-44].

The 30 December 2024 environmental finding covers those four water-management objectives, including specified flows at Columbus and Columbia and the Lake Seminole level objective [5, p.1]. The unchanged modelled navigation result provides a baseline for valuing the subsequent dredging proposal: the benefits sought from restoring the bed and providing placement capacity need their own campaign and maintenance analysis.

Carry placement readiness into the funding sequence

The September FAQ lays out the sequence after environmental study: water quality certification, additional funding, acquisition of lands, easements and rights of way, construction of disposal areas, and further appropriations for channel dredging. Continued operation and maintenance would compete nationally for federal funding through the annual appropriation process [2, p.4]. The August notice anticipated a draft supplemental EIS in spring 2027 and retained further environmental review and consultation [1, sections 5-6].

For programme development, fund the receiving sites to the date the dredging campaign needs them. The work package should identify the site-release evidence, available storage, discharge arrangement and responsibility for keeping access usable. Where those works are separately procured, their completion date becomes an input to the dredging mobilisation plan.

The upland-only and mixed-placement alternatives deserve comparable estimates using the same survey, flow case and maintenance period. Each estimate should carry its own transport route, containment construction, monitoring and subsequent site-management cost. Slough connectivity and beneficial use enter that comparison through the physical works and environmental conditions they require. The August notice includes both among the matters under consideration [1, section 3].

ACF's estimating choice combines reach, placement site and return interval. A lower excavation rate can be outweighed by a longer discharge route, an unavailable receiving area or an early second mobilisation. Keeping those costs attached to the reaches that create them gives the owner a basis for selecting the placement strategy and packaging the eventual work.