Dredging Depth Research Articles

Evaluating ecological risks and metal bioavailability in post-dredging sediments of a wetland affected by artisanal gold mining

The evaluation of metal contamination, ecological risk, bioavailability, and the environmental dredging depth in sediments of two Colombian riverine systems impacted by artisanal gold mining and agricultural activities, was conducted following dredging processes. Results indicated significant contamination by Cd and Pb before dredging, based on the contamination factor (CF) and the geoaccumulation index (Igeo). Additionally, Cu and Hg were found to cause adverse biological effects according to sediment quality guidelines. Post-dredging, surface sediments exhibited a moderate ecological risk index (RI, 150–300), primarily due to increased contamination by Hg, Pb, and Cd. To mitigate this ecological risk (RI < 150), the environmental dredging depth needed to exceed 20 cm for all metals. On average, the bioavailable fraction increased 2.3 times within two months after dredging. However, the low environmental risk (%F1 = 1–10) calculated using risk assessment codes (RAC) indicates a potential risk due to metals entering the water column and bioaccumulating in organisms. These findings provide insights into the dynamics of metals and the impact of dredging activities on sediments in the Colombian Caribbean coast affected by various anthropogenic activities. The research underscores the importance of integrating sustainable practices in mining and agriculture to protect the ecological integrity of these riverine systems.

In situ remediation mechanism of internal nitrogen and phosphorus regeneration and release in shallow eutrophic lakes by combining multiple remediation techniques

Large anthropogenic inputs of N and P alter the nutrient cycle and exacerbate global eutrophication problems in aquatic ecosystems. This study in Lake Datong, China, investigates the remediation mechanism of multiple remediation technique combinations (dredging, adsorbent amendment, and planting aquatic vegetation) on sediment N and P loads based on two high-resolution sampling techniques (HR-Peeper and DGT) and P sequential extraction procedures. The results showed that high temperature and low dissolved oxygen considerably enhanced pore water dissolved reactive P (DRP) and NH4+ concentrations attributable to abundant Fe-P and organic matter content in the sediment. Fe reduction is critical for regulating pore water DRP release and promoting N removal. Overall, for Lake Datong, combining multiple remediation techniques is more effective in controlling sediment P loads (pore water DRP, P fluxes, forms of P, and labile P), from a long-term perspective, than a single remediation. Lanthanum-modified bentonite (LMB) inactivation treatment can transfer mobile P in the surface sediment into more refractory forms over time, thereby reducing the risk of sediment labile P release. However, it is difficult to effectively remediate internal P loads owing to inappropriate dredging depths and low biomass of aquatic vegetation. Future lake restoration practices should optimize the selection of different remediation technique combinations based on internal N and P pollution characteristics, while reducing external wastewater input. These results are important for understanding the remediation mechanisms of internal N and P and provide suggestions for sediment management of shallow eutrophic lakes.

Dredging effects on nutrient release of the sediment in the long-term operational free water surface constructed wetland

Sediment is one of the key components of free water surface constructed wetland (FWS), and sediment dredging has become common practice in the long-term management of FWS. However, insufficient research has been carried out on the effects of sediment dredging in FWS, and limited information is available regarding appropriate dredging depth and methods in FWS sediment dredging. This study investigated the physicochemical characteristics of sediment in a five-year operational FWS. The effects of different dredging depths (0 cm, 1 cm, 10 cm, and 25 cm) and different dredging methods (mechanical excavation dredging and hydraulic purged flushing dredging) were compared based on the improvement of overlying water quality via indoor static simulating experiments. The results showed that the 0–10 cm depth of sediment was heavily contaminated by organic matter and nitrogen, and slightly contaminated by phosphorus. A boundary layer (0–1 cm) was formed with obvious different physicochemical characteristics which could suppress nutrient release into the overlying water. The 25 cm dredging depth was the appropriate dredging depth according to engineering practice and control performance of water quality. The pollutant diffusion fluxes of 25 cm dredged depth were 31.8%, 58.3%, 30.7%, 41.5% and 20.6% lower than those of undredged sediment for total phosphorus, soluble reactive phosphorus, total nitrogen, ammonia nitrogen, and permanganate index, respectively. Mechanical excavation dredging had a better control of water quality than hydraulic purged flushing dredging due to the low sediment water content and low residual sediment on the dredged sediment surface.

Vessel Size and Dredging Depth Optimization for Tol Laut Program using Genetic Algorithm: Hub Port Case Study

Tol Laut is an Indonesian government containerized sea freight program which is aimed at reducing the price disparity, as well as extending logistic distribution from developing regions. The program can be enhanced by determining the optimum dredging depth of port navigation channel and the optimum size of vessel. The required channel depth is affected by the size of vessel, which is represented by its draft, on the respected hub port. The significance of vessel size and dredging depth in accommodating the container demand will be evaluated by considering the physical environmental conditions such as surface water elevation which affected by tidal conditions. Genetic Algorithm is utilized in this study since it showed robust results on optimizing port performances problems that have many dependent variables and solutions. As a hub port within Tol Laut Program, Port of Belawan is selected as a case study due to its strategic location. Several demand scenarios were run using the algorithm, resulting several channel depth-vessel size pairs as the solution. In conclusion, the feasibility of the dredging activity relies significantly on the growth of the demand.

A method of assessing the depth of contaminated sediments that should be removed in lakes: a case study of Tangxun Lake, China.

The depth of contaminated sediments constrains the water environment of large shallow lakes and can affect shallow lake water quality through sediment resuspension and nutrient release. Although such effects can be avoided by sediment dredging methods, we still cannot precisely quantify the depth of sediment dredging. Therefore, we used organic index method, pollution index method and potential ecological risk evaluation to evaluate the contamination status of split samples of in situ sediments layer by layer, and established a comprehensive contamination index evaluation method for layer-by-layer sediments, then combined with the contamination release characteristics of split samples to assess the contamination degree of the sediments obtained. The results show that the content of nitrogen and phosphorus in the surface layer of Lake Townsend sediments is generally higher than that in the middle and bottom sediments, and the heavy metals also satisfy this pattern, which is consistent in the sediments of both east and west regions. We also simulated the release process of nitrogen and phosphorus nutrients in the in situ sediment of Tangxun Lake in 2019, and the experimental results showed that the risk of nitrogen and phosphorus nutrient release in the sediment was mainly concentrated in the surface and middle layers, and the risk of elemental nitrogen release was significantly greater than that of phosphorus release. Finally, a comprehensive evaluation was carried out to obtain the desilting depth of the sediments in Lake Townsend, and it can be determined that the recommended desilting depth is about 20cm for West Lake and 30cm for East Lake. The results show that the recommended dredging depth can be determined based on this method, which provides an important scientific basis for sediment dredging in Tangxun Lake and even provides a new paradigm for sediment dredging depth estimation in similar large shallow lakes.

Identification of Dredging Depths Based on Sediment Vertical Distribution Profiles of Total Nitrogen and Total Phosphorus and Their Adsorption-desorption Equilibria

A dredging demonstration project in the Baiyangdian Lake included open waters and fishing ponds to reduce the internal release of nitrogen and phosphorus from bottom sediments. The dredging depth design was determined by both the sediment vertical distribution profile of total nitrogen and phosphorus, and the sediment adsorption-desorption equilibrium method. The determined dredging depths were very similar and coincident. The dredging depth for the demonstration area of open waters in Nanliuzhuang was identified as(50±10) cm; and the dredging depths for fishing ponds were(30±10) cm in both the Nanliuzhuang and Caiputai demonstration areas. The equilibrium nitrogen(NH4+-N) and phosphorus(SRP) concentrations at zero net sorption or desorption(ENC0 and EPC0) were significantly positively correlated with both exchangeable and total nitrogen and phosphorus in the sediments. The total nitrogen and phosphorus in the sediments were also used to predict the risk of their release from the bottom sediments to the overlying water column. The sediment layers with ENC0 and EPC0 values greater than the NH4+-N and SRP in the overlying water column indicated the sediments act as a source of dissolved nitrogen and phosphorus to the overlying water column in the Nanliuzhuang and Caiputai demonstration areas. Accordingly, the sediment layers with both total nitrogen concentrations greater than 750 mg·kg-1 and total phosphorus concentrations greater than 500 mg·kg-1 should be identified as dredging layers.

BEHAVIOUR OF LATERALLY ANCHORED RETAINING SYSTEM IN LOOSE SAND SOIL

One of the earliest earth retention technologies used in civil engineering projects is sheet pile walls. Therefore, in this work, a numerical analysis using Plaxis 2D was performed to investigate the behaviour of laterally anchored retaining system in sandy soil, focusing on the anchor force, lateral displacement, and maximum bending moment. The effects of anchor location and number on wall and soil deformations were investigated for various wall heights. When anchored-sheet-piles were used instead of cantilever sheet piles, the results showed a significant reduction in both wall deformation and bending moment specially at high dredging levels. In addition, while having numerous anchor levels is the most approach to minimize wall and soil deformations. Also, the findings revealed that adopting the one-anchored sheet pile wall can greatly decrease the maximum wall displacement by about and 59.16%; which occurs at 0.4H; as well as reduce the maximum bending moment by about 85.63%; which occurs at 0.5H, comparing with the cantilever sheet pile wall at dredging depth (H) = 5m. At a deeper dredging depth (H=9m), the maximum lateral displacement and maximum of wall were reduced by 88 %, and 86 %, respectively. Also, at H= 9m, using the second level of anchors can also reduce the maximum bending moment on the wall by more than 83.55 %.

Modeling tidal sand wave recovery after dredging: effect of different types of dredging strategies

Maintenance of navigation channels in shelf seas with tidal sand waves usually requires repeated dredging operations. Optimizing these interventions is a difficult task, particularly complicated by the nonlinear morphodynamics of sand wave recovery after dredging. Here we present a process-based model study, incorporating different strategies of dredging in an existing nonlinear sand wave model. We consider ‘topping’ (removing sand from crest) and ‘swiping’ (same, but now placing it in the troughs), for a range of dredging depths. Starting point is a fully developed sand wave or sand wave field, as simulated in the model. Results indicate that sand wave recovery is slowest after swiping. Also, larger dredging volumes imply longer recovery times. Next, we study the maintenance intervals and (cumulative) dredging volumes resulting from adopting a typical temporal strategy: swipe to a prescribed dredging depth, as soon as the recovering sand wave crests have reached a critical depth. Maintenance intervals are found to depend on the dredging depth and, importantly, to vary over time, as well. This last result shows that sand wave recovery depends not only on height, but also on its shape, emphasizing the limitations of existing, empirical (Landau-type of) models based on amplitude (or height) only.

Влияние капельного орошения на рост и развитие саженцев сливы в питомнике в условиях Центрального Нечерноземья России

One of the possible ways to ensure safety is to use drip irrigation, which also improves the quality and productivity of crops. The aim of the work is to study the availability of moisture in the soil for the growth and development of cream seedlings grown in a fruit nursery in the conditions of the Non-Black Soil Zone of Russia. Research conducted on the lands of the educational experimental farm of the fruit-growing laboratory «Michurinsky Garden» of the Russian State Agrarian University – Moscow Timiryazev Agricultural Academy in 2018 and 2019. The results of field experience indicate that for a more rational use of irrigation water and obtaining highquality vegetable oils in the nursery, it is recommended to use an irrigation regime with maintaining soil moisture in the range of 80–100 % lowest moisture capacity with a dredging depth of 30 cm in the first year and 40 cm in the second year.

Assessing the Hydrodynamic Response of the Mar Menor Lagoon to Dredging Inlets Interventions through Numerical Modelling

The Mar Menor lagoon has been subjected to high anthropogenic pressures. Among them, in the early 1970s, dredging and enlargement of one of the inlets to make a navigable channel has had strong consequences on the hydrology, ecology, and fisheries of the lagoon. In recent years, changes in agricultural practices have induced an eutrophication process, leading to loss of water quality. As a solution, some management proposals have included dredging of the inlets in order to increase the water renewal. However, these proposals did not take into account the negative effects of previous experiences nor the consequences on environmental conditions of the lagoon and therefore on biological processes. The purpose of this work is to assess the effect that proposed mitigation measures, could have on the hydrodynamic conditions and discuss its possible ecological consequences. A three-dimensional (3D) numerical model has been used to simulate the lagoon under different dredging scenarios, covering different dredging depths and extensions. The simulated current fields and fluxes through the inlets, as well as water renewal times have been compared for the different scenarios. It is found that some of the considered scenarios take the system beyond the threshold of sustainability, where the modified current dynamics could affect sediment transport, beach dynamics and fishing capacities in a significant way. Water exchange with the Mediterranean is also strongly affected, with consequences for species connectivity, and a homogenization of the water renewal times that could lead to loss of ecosystem heterogeneity and structural complexity. The study demonstrates the utility of numerical models as effective tools for the management of coastal areas.

Vertical Profile of PAHs and Dredging Depth of River Sediments

Sediment dredging is an effective engineering measure to reduce the negative effects of PAHs pollution on water environment. The dredging depth is a key parameter in environmental dredging engineering. A guidance of environmental dredging depth needed to reduce the toxicity risk was developed which was specifically designed for the removal of river sediments contaminated by PAHs based on the mean effect range median quotients (mean-ERM-q). The dredging depths for removing river sediments were calculated based on the vertical profile of PAHs content and the quality guidelines of sediment. Pinghu water system was carried out to determine the dredging depths of sediments from nine rivers by the proposed method. Each sediment core was collected from different river. The results showed the profiles of PAHs in sediment cores were irregular and diverse due to river dredging events and human activities in different periods. The risk assessment of PAHs toxicity showed one of nine cores with moderate-high probability, 4 of nine cores with low-moderate probability and the others with low toxicity risk. The achievement can offer a reference to the dredging engineering in other similar river systems.

Evaluation of nutrients and heavy metals in the sediments of the Heer River, Shenzhen, China.

The parameters of water contents, oxidation-reduction potential, organic matter, total phosphorus, total nitrogen and heavy metals concentrations of mercury (Hg), cadmium (Cd), lead (Pb), arsenic (As), chromium (Cr), copper (Cu) and zinc (Zn) in surface sediment and their vertical distribution incore sediments of the Heer river were investigated. Evaluation of nutrients and heavy metals in the Heer River sediments was done by pollution index and potential ecological risk index (PERI) method, respectively. Environmental dredging depth was calculated. The parameters pH, water content, total nitrogen (TN), and organic matter (OM) as well as heavy metals decline with the increased depth. Nutrients of TN, total phosphorus (TP), OM, and heavy metals Cd, Cu, and Pb were classified into the same group and there were significant positive correlations according to the principal component analysis and Pearson correlation, implying that they have a common origin. The results of high pollution index value of OM, TP, and TN of surface sediment obtained from this research showed that the Heer River was in serious nutrient pollution. The contributions of individual metals to the potential ecological risk were in the following order: Cd > Cu > Ni > Cr > Zn > As > Pb. Cd presented serious ecological risk and contributed most to the sediments of the Heer River. The ecological risk (RI) was at a considerable high risk level, and therefore, the environmental dredging depth of the Heer River is 94cm for the purpose of reducing heavy metal contamination of the Heer River.

Use of multi-objective dredging for remediation of contaminated sediments: a case study of a typical heavily polluted confluence area in China.

Sediments in confluence areas are typically contaminated by various pollutants that have been transported there by inflowing rivers. In this study, we evaluated the pollution status of a confluence area in Lake Chaohu (China). Both the nutrients and hazardous pollutants were analysed. Most sediment cores showed large variations in nutrient concentrations at depths of 10 to 18 cm. Positive release rates of NH4(+)-N and PO4(3-)-P were detected in sediment cores. Hg and Cd were the most typical problematic metal contaminants encountered, and their contamination levels extended to depths of 20 and 25 cm, respectively. Polycyclic aromatic hydrocarbons (mostly acenaphthene and fluorine) were the primary persistent organic pollutants (POPs) present in sediments, and contamination levels frequently could be detected up to a depth of 16 cm. Simulated dredging operations were implemented in the laboratory, with a dredging depth of 15 cm found to be suitable for nutrient suppression. With the goal of suppressing nutrients release and removing high-risk metals and POPs, a multi-objective dredging plan was developed. This plan subdivides the confluence area into five parts that were treated with different dredging depths. A demonstration area was dredged in the most heavily polluted part, and the observed dredging effects were consistent with those expected on the basis of the plan. Such an approach to dredging might also be useful in other areas in the future.

Calculation of the environmental dredging depth for removal of river sediments contaminated by heavy metals

Sediment contamination by heavy metals can result in significant damage to the ecological water environment. Sediment dredging is a useful way to reduce the adverse effects of heavy metal pollution in freshwater. The dredging depth is a key parameter in environmental dredging engineering. In this paper, we propose an innovative method called the critical-risk-depth method for calculating the environmental dredging depth that has been specifically designed for removal of river sediments contaminated by heavy metals. To determine the critical risk depth for dredging, the heavy metal concentrations at different sediment depths and their potential ecological risks must be tested and evaluated. The first step of the method involves analyzing sediments to determine the lateral and vertical distribution of heavy metals. In the next step, Hakanson’s potential ecological risk index is used to assess the ecological risk of heavy metals at different sediment depths. Finally, the recommended environmental dredging depths are calculated based on the potential risk for change in the vertical distribution and the given threshold level for the potential critical risk from heavy metals. We carried out a case study to determine the dredging depth for river sediment in Pinghu. The sediment analysis results show that the contents of Cd, Zn, and Pb are excessive when compared with the local soil background levels. Because of the accumulation effect of heavy metals in sediments, the heavy metal contents tend to decrease with sediment depth, but this trend may change as a result of human activities and other river dredging events. There is a high potential ecological risk level from heavy metal pollution in sediments in the study area, and the recommended environmental dredging depths of the ten rivers range from 35 to 100 cm.

Precontrol of algae-induced black blooms through sediment dredging at appropriate depth in a typical eutrophic shallow lake

Algae-induced black blooms, which trigger both the collapse of lake ecosystems and crises in urban water supplies, have become a serious ecological problem in numerous eutrophic shallow lakes. Therefore, preventing and suppressing the outbreak of black blooms is critical for maintaining the health of lake ecosystems. In this study, sediment dredging was employed as a black bloom precontrol method, and the effects of different dredging depths (0cm, 7.5cm, 12.5cm, and 22.5cm) were compared regarding the prevention of black bloom formation. Drained algae (mostly cyanobacteria) were added to these treatments at a density of 5000g/m2. The main physical and chemical characteristics of the water and sediment important for black blooms were analyzed during the study. The results showed that dredging was unable to suppress the offensive odor of the algal bloom. High concentrations of volatile organic sulfur compounds due to algal decomposition were detected in all of the added-algae treatments. Black blooms occurred in the undredged (UDR), 7.5cm dredged (7.5DR), and 12.5cm dredged (12.5DR) treatments but did not occur in the 22.5cm dredged (22.5DR) treatment. Therefore, black blooms can be suppressed by sediment dredging at an appropriate depth (22.5cm in the current study). The ∑H2S concentrations in the water samples of the 22.5DR treatment were remarkably lower than in the other added-algae treatments during the experiment. Hence, ∑H2S, as compared to DO, Eh, pH, and Fe2+, was considered as the most important limiting factor in the overlying water for black blooms. Two major reasons may have caused the low ∑H2S concentrations and suppressed the black blooms: (a) low levels of acid-volatile sulfide in the sediment after dredging (22.5cm) may have reduced the release of hydrogen sulfide to the overlying water, and (b) the low porosity (≤60.5%) observed after dredging is unconducive to pollutant diffusion and migration in sediments, which may have suppressed the release of Fe2+ and ∑H2S into the overlying water.

Probabilistic Model for Predicting Ship Underkeel Clearance: Field and Laboratory Validation

This paper presents validation comparisons between field and laboratory measurements and a new probabilistic model for predicting ship underkeel clearance (UKC). Prototype ship motions and environmental data were obtained in May 1999 in the deep-draft entrance channel at Barbers Point, HI. These field measurements were reproduced in controlled laboratory studies in 2000 and 2002 with a model of the World Utility (WU) bulk carrier. These measurements constitute some of the data being used to validate the Corps's Channel Analysis and Design Evaluation Tool (CADET), a suite of programs to determine the optimum dredge depth for entrance channels. In general, the CADET predictions matched the field and laboratory measurements within cm-accuracy for wave heights that ranged from 45 cm to 75 cm.

A framework for the integrated assessment and management of dredged materials in Italy: a case study based on the application of Local Sediment Quality Guidelines

In order to assess sediment quality and to account for the great geochemical heterogeneity of Italian coasts, Local Sediment Quality Guidelines (LSQGs) have to be defined for specific portions of the coastline based on the approach developed by ICRAM–APAT (2007). This paper describes the application of LSQGs to the harbour of Fiumicino (Rome, Italy). The aims were to evaluate the quality of dredging sediments through an integrated chemical–ecotoxicological approach and to define suitable management options. Thirty-eight sediment cores, covering the planned dredging depth, were collected in the study area and sliced into 92 sediment samples. Chemical analyses, including inorganic and organic contaminants as well as microbiological parameters, were carried out for all the samples. A bioassay battery composed by the bacterium Vibrio fischeri, the sea urchin Paracentrotus lividus and the alga Dunaliella tertiolecta was applied on one third of the samples. LSQGs were derived from chemical and ecotoxicological data of the harbour area, and were integrated with those from the identified dumping site. The Baseline Chemical Level, corresponding to an absent or unlikely ecotoxicological hazard, and the Limit Chemical Level, corresponding to a probable ecotoxicological hazard, were the LSQGs derived for each chemical. A gradient of increasing contamination, moving inland due to urban and agricultural effluents, was observed. Ecotoxicological analyses, similar to microbiological ones, confirmed the poor sediment quality, with the exception of a sample located at the port entrance, where hydrodynamics flush sediment away from the site. Principal component analysis allowed a clear discrimination of three areas, each affected by a different contamination degree and influenced by many sources related to industrial, commercial and/or urban activities. Using LSQGs and the results of bioassays, it was possible to classify the sediment quality of the whole harbour area and to define the most suitable management options. It was found that Fiumicino harbour sediment was not suitable for either beach nourishment or for offshore dumping, with the exception of a negligible amount located at the port entrance. In turn, most sediment seemed to be suitable for disposal in a properly sealed confined disposal facility or for mechanical/chemical treatment. This case study provided useful insights for implementing the development of LSQGs for more realistic sediment management and will assist in promoting its application to harbour dredging at the local level.

Validation of a Risk-Based Numerical Model for Predicting Deep-Draft Underkeel Clearance

AbstractThe channel analysis and design evaluation tool (CADET) is a numerical program to determine the optimum dredge depth for the offshore portions of entrance channels. A brief description of the theoretical basis and risk assessment in CADET is presented. Validation comparisons between CADET predictions and field measurements of wave-induced vertical motions at Ambrose Channel, New York, are presented. Prototype ship motions were measured with a differential global positioning system in April 1998 along three 488-m-long reaches. Comparisons were made with six ships, three tankers and three containerships, during inbound and outbound transits. In general, the CADET predictions matched the field measurements reasonably well, especially considering the wave heights were relatively small during the measurement period.

Pipeline Dredge Analytical Program with Comparison to Field Data

A clear understanding of pipeline dredge production capacity provides dredge operators and dredging project planners with the capability to accurately and effectively determine a project’s cost and duration. Dredge pump and pipeline hydraulics coupled with slurry transport principles present a complex and challenging engineering system requiring specialized knowledge and understanding of how the system will operate. This study determines how well the theoretical principles of hydraulics and slurry transport govern the actual pipeline dredging process, compared with dredge pump and pipeline instrumentation data. Results indicate that the delivered pipeline slurry mixture incurred more friction losses during transport than water alone. This study further determines the maximum pumping capability of the dredge pump in terms of its maximum dredging depth and maximum pipeline length. These results determine that the pipeline dredge operated well within its operating limits during the case study. Overall, the c...

Partial and total factors of safety in anchored sheet pile design: Discussion

Valsangkar and Schriver have contributed to furthering the use of limit state design methods in geotechnical engineering. The title of the paper implies partial safety factors for anchored bulkhead design, but the only limit state that was examined was kickout. Design of the bulkhead requires examination of a number of other limit states including anchor rod capacity, sheet pile yield, wale yield, and anchorage capacity (Navfac 1986), and all of these use soil and water pressures in their formulation. It would be desirable to use, for example, the same resistance factor for the soil friction angle for each limit case. To establish the adequacy of the recommended partial safety factors, the other limit states for an anchored bulkhead should also be compared with conventional design. An interesting outcome of this paper is that with the proposed partial safety factors for limit state design, the sequence of solving of statics problem, i.e., how water pressures are introduced into the moment equation, affects the design. The authors recommend that commentary be included in the Canadian Foundation Engineering Manual (Canadian Geotechnical Society 1985) to clarify this point. The partial safety factors discussed by the authors are applied to the loads and resistances in the design and are used to account for uncertainties in these values. However, implicit in these factors are components that account for uncertainties in the dimensions and method of analyses used. Water has no shear strength and virtually no variability of unit weight. The quantity that causes variability in the water pressures is the water level difference, i.e., a dimension. In some cases, such as this water level difference, should a separate factor be considered that would be applied directly to the dimension before being used in the limit state equation? If applied in this case, the sequence of incorporating water pressures in the moment equation would not change the design. For anchored bulkheads in particular, another dimension that should be considered for a separate factor is the dredge depth in front of the bulkhead. Dredging, which often occurs on a regular basis during the life of a bulkhead, may give a higher variability to the passive pressure than would normally be experienced with passive pressure being used in other types of design. Terzaghi (1954), Tschebotarioff (1973), and Navfac (1986), among others, recommend an increase in the embedment depth to account for this. Since this type of partial safety factor is thus used by many in conventional design, more widespread use of a partial safety factor applied to dimensions in limit state design should perhaps be considered.