Hydraulic Loading Conditions Research Articles

Feasibility of sequential anaerobic-aerobic integrated settler-based biofilm reactor for onsite treatment of domestic wastewater

The present study investigates the applicability of sequential anaerobic aerobic integrated settler-based biofilm reactor (SAABR) for the onsite treatment of domestic wastewater. The main aim of the study is to overcome the inherent flaws in an anaerobic system as well as enhancing the effluent quality by means of aerobic post-treatment. The sequential system consisted of an anaerobic settler is followed by two biofilters, anaerobic as well aerobic in series. The first biofilter is anaerobic and the second one is aerobic. The system was run on two hydraulic loading conditions (steady and non-steady flow) with a 24-hour hydraulic retention time (HRT) for the anaerobic system and a 2-hour HRT of aerobic filters. It was found that the performance of the system at steady flow stood at 93.9 ± 2.6, 93.3 ± 1.8, 91.2 ± 4.2, 75.8 ± 3.8 and 98.7 ± 1.1% in terms of total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN) and faecal coliform (FC), respectively while at non-steady flow, it decreased slightly. The Field Emission Scanning Electron Microscope (FESEM) showed the presence of anaerobic bacteria in the system. The system is able to overcome the major flaws of the anaerobic systems and able to deliver high effluent quality. The study demonstrated that the sequential system can be a sustainable alternative for the onsite treatment of domestic wastewater, particularly in rural areas of the developing countries like India.

Soil Erosion Due to Defective Pipes: A Hidden Hazard Beneath Our Feet

Sinkholes are a significant underground hazard that threatens infrastructure and lives and sometimes results in fatalities. The annual cost of sinkhole damages exceeds $300 million, although this estimate is likely underestimated due to the need for national tracking. Sinkholes can also alter natural drainage patterns, leading to increased flood risk. While natural sinkholes occur, those in urban areas are predominantly manmade, caused by soil erosion from defective pipes, typically due to aging. Climate change, storm surges, and urbanization have accelerated subsidence in urban environments, posing greater risks to critical infrastructure and densely populated areas. Extensive research has focused on soil erosion in dams; however, this knowledge does not necessarily apply to erosion through orifices, where gravity and other factors play significant roles. This paper presents a critical literature review on internal soil erosion due to defective pipes (SEDP). The review highlights that hydraulic loading, backfill type, and pipe conditions (defect shape, size, and depth) influence SEDP. Key findings from experiments and numerical studies are summarized, while mechanisms and knowledge gaps are identified. However, it is concluded that the current understanding in this field remains limited, underscoring the urgent need for further experimental and numerical research to expand the knowledge base on SEDP.

Spatial and Temporal Evolution of Particle Migration in Gap-Graded Granular Soils: Insights from Experimental Observations

This study presents physical observations and insights into particle migration characteristics throughout the suffusion process. Using a purpose-built coaxial permeameter cell, suffusion experiments were conducted on idealized internally unstable gap-graded granular soils at varying fines content and hydraulic loading conditions. The specimens were prepared with a mixture layer comprising finer and coarser fractions underlying a coarse layer composed of the coarser fraction alone. This enabled the finer fraction within the mixture layer to migrate through the coarse layer with upward seepage flow. The local porosity profile along the specimen was determined using spatial time-domain reflectometry and an inversion algorithm, which enabled the development of a novel field map of the difference in porosity from the initial condition. This field map provided a visual guide of the spatial and temporal variation in porosity and enabled particle migration internally within the specimen to be quantitatively characterized from onset to progression to washout. The limiting onset condition identified from the field map was shown to be comparable to that obtained using conventional approaches, thereby providing strong validation for the application of porosity-based field maps. As suffusion progressed, the height of infiltrating finer particles into the coarse layer increased linearly with time, while the overall rate of particle migration from the mixture layer to the coarse layer evolved in a non-linear manner with the rate of migration increasing as the specimen reached a complete mixture condition, where the finer fraction infiltrated the entire coarse layer. The attainment of a complete mixture condition was dependent on the fabric of the gap-graded soil. Specimens with an underfilled fabric showed a gradual migration process, while specimens with a transitionally underfilled fabric resulted in minimal particle migration followed by a very rapid formation of the complete mixture.

Internal erosion in hydrophobic and hydrophilic soils

The water repellency of soil occurs when organic matter coats the soil particle surface; this can either happen naturally due to wildfire and fungal growth or be induced by chemical treatments. The internal stability of water-repellent soils subjected to seepage has not been explored in the literature. In this study, the mechanical responses to internal erosion in three synthetic water-repellent soils, treated by different organic matters, were first investigated using a modified stress-controlled triaxial apparatus. The degree of hydrophobicity of the test soils was assessed through the measurement of apparent water contact angle. In each internal erosion test, the cumulative particle loss, deformation and hydraulic conductivity were evaluated. The water-repellent coatings efficiently suppressed the progression of internal erosion at practical hydraulic gradients because of their smaller fluid–solid adhesion. Continuously increasing the hydraulic gradient would finally result in a breakthrough of internal erosion due to the saturation of the hydrophobic soils under high pore-water pressures. Post-erosion contact angle measurements and scanning electron microscopy images confirmed the durability of the three water-repellent coatings against seepage erosion. The findings of this study confirm the potential of applying hydrophobic soils to mitigate internal erosion under normal hydraulic loading conditions.

Physical observations of the transient evolution of the porosity distribution during internal erosion using spatial time domain reflectometry

A purpose-built permeameter was used to explore the transient evolution of porosity during the mixing process in filtration experiments. The experiments considered upward seepage flow and explored the influence of base and filter particle sizes, along with different hydraulic conditions. The permeameter acted as a coaxial transmission line enabling electromagnetic measurements based on spatial time domain reflectometry, from which the porosity profile was obtained using an inversion technique. Quantitative characteristics of the onset and progression of the mixing process were extracted from a porosity field map. The limiting onset condition was influenced by geometric and hydraulic factors, with the critical flow rate exhibiting a strong dependence on the base particle size, while the critical hydraulic gradient exhibited a stronger dependence on filter particle size. The progression of the mixing process was characterised by both the transport of base particles into the filter layer, as well as the settlement of the filter particles into the base layer due to the reduction of the effective stress at the base–filter interface leading to partial bearing failure. The rate of development of the mixture zone was strongly dependent on the hydraulic loading condition and the base particle size, but the final height of the sample after complete mixing was independent of the hydraulic loading path.

Pollutant removal from swine wastewater and kinetics in constructed rapid infiltration system (CRI system)

ABSTRACT The purpose of this paper is centred on the kinetics of removal of main pollutants in wastewater and to compared different hydraulic loading conditions of the constructed rapid infiltration system (CRI system) in terms of removal efficiencies, effluent concentrations, mass removal rate (MRR), and the first-order removal rate coefficient (k) of COD, TOC, NH4 +-N, TN, and TP. The results showed that the higher the hydraulic loading, the higher the effluent concentration. The results that synthesized hydraulic loading, effluent concentrations, removal efficiencies, and other conditions showed that the best hydraulic loading was 40 cm/d. When the hydraulic load was 40 cm/d, the effluent average concentrations of COD, TOC, NH4 +-N, TN, TP, Cu2+ and the removal efficiencies were 27.31 ± 16.40 mg/L, 86.11%, 10.55 ± 5.25 mg/L, 84.64%, 0.59 ± 0.87 mg/L, 99.60%, 143.31 ± 14.77 mg/L, 7.04%, 5.64 ± 1.38 mg/L, 79.20%, and 0.13 ± 0.47 mg/L, 97.51%, respectively. According to a kinetic study of the primary pollutants, the MRR increased with an increase in the hydraulic loading, except for ammonia nitrogen. CRI-3, CRI-4 were high significant correlated with ammonia nitrogen (with R 2 = 93.65% and R 2 = 95.03%, respectively), while CRI-2, CRI-3, and CRI-4 were high significant correlated with total nitrogen (with R 2 = 94.56%, R 2 = 96.70% and R 2 = 96.56% respectively).

Comparison between a single unit bioreactor and an integrated bioreactor for nutrient removal from domestic wastewater

The simultaneous nitrogen and phosphorous removal efficiency of Bacillus cereus GS-5 immobilized single unit packed bed bioreactors was compared with that of integrated bioreactors. Both the single unit and integrated bioreactors were fed with domestic wastewater (NH4+-N 70 mg/L, NO3–-N 70 mg/L and PO43--P 15 mg/L) under 300–1000 mg/L carbon loading and 7.2–28.8 L/d hydraulic loading rates. The removal efficiencies of NH4+-N, NO3–-N and PO43--P in the integrated bioreactor were 94.2%, 92.3%, and 97.6%, respectively, which are slightly better than the single unit bioreactor. The specific oxygen utilization rate (SOUR) showed that the integrated bioreactor (17.06 mg-O2/g-MLSS/h) has a higher microbial activity than the single unit bioreactor (15.2 mg-O2/g-MLSS/h). Both the single unit and integrated bioreactors successfully resisted the organic as well as hydraulic shock loading conditions. This work established promising application prospects of both single unit fixed bed and integrated bioreactor for nutrient removal from domestic wastewater.

Hydraulic characteristics of integrated settler based biofilm reactor as onsite sanitation system

Abstract The present study identifies the hydraulic efficiency of a novel onsite sanitation system at variable hydraulic shock loading conditions. The system consisted of three chambers, each working as an up-flow anaerobic bioreactor, accommodated within a single unit. The hydraulic characteristics were identified with the help of residence time distribution (RTD) analysis by step feeding of lithium chloride (LiCl) solution into the system. The experiments were run at variable hydraulic loading conditions at different peak flow factors (PFF) of 1, 2, 4 and 6 while maintaining 24-h hydraulic retention time. As revealed in the RTD analysis, the biofilm reactor achieved a very good hydraulic efficiency that varied from 0.76 to 0.81 at PFF 1, 2 and 4. Although in the case of PFF6, it was comparatively low. It was noted that the dispersion number was always below 0.2 at variable hydraulic shock loading conditions under different PFFs, which indicated that the reactor behaved perfectly between mixed-flow and plug-flow reactor. The system was also able to achieve good pollutant removal efficiency for chemical oxygen demand (COD) and total suspended solids (TSS) under all PFFs, which was more than 68 and 75%, respectively.

Performance of an Integrated Settler Based Anaerobic Biofilm Reactor as Onsite Sanitation System

The present study analysed the performance of an integrated settler based anaerobic biofilm reactor (ISBABR) for domestic wastewater treatment at two hydraulic loading conditions as an onsite sanitation system. The ISBABR is designed on the basic concept of conventional septic tanks and anaerobic biofilm reactors. The ISBABR was run on actual sewage after inoculating it with digested sludge, whose COD (Chemical oxygen demand) and VSS (Volatile suspended solids) values were 9.65 and 7.13 g/l respectively. The system was operated on steady and non-steady hydraulic loading conditions while maintaining 24 h HRT for 4 consecutive months. The average removal efficiency of the system in terms of TSS (Total suspended solids), BOD (Biochemical oxygen demand) and COD was found to be 90.09 ± 4.5%, 89.89 ± 3.2% and 87.89 ± 5.2% respectively, under both the hydraulic loading conditions. In bacterial analysis, the removal efficiency of the system in terms of TC (Total coliform) and FC (Fecal coliform) was found to be 85.5 ± 4.9% and 96.36 ± 1.5% respectively. The morphology of the sludge showed the presence of anaerobes, which was a good indicator for the system. The results of the present study prove that the ISBABR is perfect system for onsite sanitation.

Investigation of the plastic hardening of metal thin-walled tube under pulsating hydraulic loading condition

In the present study, the mechanical model of section element in tube bulging area was established through the stress conditions of hydraulic bulging. Based on the mechanical model, the equivalent stress and equivalent strain equations of the section element in the bulging area were derived, respectively. Combined with the experimental data, the equivalent stress and strain of the section element in the bulging area were fitted by polynomial, and the plastic hardening model of thin-walled tube under pulsating loading was obtained. In order to verify the model precision, the plastic hardening models obtained from pulsating hydroforming and non-pulsating hydroforming were taken as the material model by finite element simulation respectively. The experimental results were compared with the simulation results which showed that as a pulsating hydraulic loading material parameters, the model established in this paper had higher precision.

Removal of nitrogen from rainwater runoff by bioretention cells filled with modified collapsible loess

The construction of bioretention facilities in collapsible loess areas faces some problems such as low infiltration rate of rainwater runoff and system blockage, which seriously affect the treatment effect of bioretention cell on rainwater runoff. According to the different filler matrix, three bioretention cells with improved filler were constructed, the 1# bioretention system was filled with 50% of the construction waste mixed with 50% loess, and the 2# bioretention system was filled with 50% concrete sand mixed with 50% loess, the 3# bioretention system was filled with 45% concrete sand +10% wood chips +45% loess mixed in the bioretention cell. The results show that the removal rate of NH4+-N is the highest when the height of the inundation zone of the bioretention cell is 600 mm (more than 98%). The change of hydraulic load and submerged zone height had a significant effect on the removal rate of NO3−-N in bioretention cell (P < 0.05). The removal rate of NO3−-N in the bioretention cell decreased with the increase of hydraulic load, and the bioretention cell had the highest removal rate of NO3−-N (48.85%) under low hydraulic load conditions. The removal rate of NO3−-N in the bioretention cell increased with the increase of the height of the inundation area, and the removal rate of NO3−-N was the highest when the inundation area height of the bioretention cell was set at 600 mm (98.33%). The improved bioretention cell has a better effect on NH4+-N treatment during the wet period, and the NH4+-N concentration of the effluent is below 0.4 mg/L. The NO3−-N concentration in the effluent of the three improved bioretention cells during the wet period differed greatly. Among them, the bioretention cells using sawdust modified fillers had the highest removal rate of NO3−-N. The collapse amount of the three improved bioretention cells was below 0.5 cm, and the permeability coefficients were above 2 cm/h. The experiment proves that the three methods to improve the collapsible loess filler can be applied to the construction of the bioretention cell in the collapsible loess area so that the bioretention technology can be effectively promoted in the loess area. This experiment has great significance to the construction of bioretention cells in the loess area.

Mathematical modelling of cumulative erosion ratio for suffusion in soils

Internal erosion induced by suffusion is a progressive process that can have negative consequences for dams, foundations and tunnel projects. The erosion ratio (denoting the ratio of the weight of cumulative eroded soils to the total weight of soils) is an important parameter in characterising this process, reflecting variations in porosity and hydraulic conductivity during suffusion. In this study, an erosion equation expressing the variation in the erosion ratio with respect to the hydraulic gradient and time is derived under arbitrary hydraulic loading conditions. This equation is based on investigations into the influence of both the hydraulic gradient and of time on the process of soil erosion. The derived erosion equation is applied in a case study and the results are compared with existing test data. It is shown that the expression proposed in this paper is in good agreement with observations. Finally, the influences of the hydraulic loading history and an erosion rate coefficient on the soil erosion process are discussed.

REALITY IN PACKAGE ON-SITE GREASE TRAP PERFORMANCE: SUCCESS AND FAILURE IN FOG REMOVAL

Package on-site grease traps are widely used in household and restaurant in Thailand for oil and grease removal although frequent failures in FOG removal have been reported. Theoretically, too small of operating hydraulic retention time (HRT) takes the blame, but some suppliers claim that their grease traps can be well operated even with HRT of 15 minutes. This study was to investigate the performance of grease trap with various HRTs (15 minutes to 20 hours) and FOG concentrations in the feed (50 to 600 mg/l). Results showed that the operating HRTs of 15, 30 and 60 minutes could represent a kind of shock hydraulic loading condition, which insufficient FOG removal efficiencies were observed. Also, the experiment to enhance the grease trap’s performance was set up by withdrawing certain volume of grease trap waste. The operating HRT of 60 minutes with the feed contained FOG of 200 mg/l and dishwashing detergent of 0.5% (v/v) was investigated for seven-day period. The experiment without daily withdrawal was operated in parallel as a control. The results showed that the FOG removal efficiencies in the control began to fall down to 50% on the fifth day of operation. The experiment with daily withdrawal showed more stable FOG removal efficiencies, which its efficiencies was still higher than 50% after seven days of the experiment. However, this could be said that the 15-litre package on-site grease trap fed with operating HRT of 60 minutes (or lower) could not maintain sufficient removal efficiency for long period (months).

Waste Brick as Constructed Wetland Fillers to Treat the Tail Water of Sewage Treatment Plant.

Adopting the concept of "using waste to treat waste", the waste bricks will be used for constructed wetland filling. Integrated vertical-flow constructed wetland (IVCW) studied on the purification effect in influent water under three hydraulic loads (0.15, 0.25, 0.35m/day). The results show that the waste bricks can be used as the carrier for the growth of the system biofilm, and have positive effects on the removal of pollutants in the influent water. Under three different hydraulic load conditions, the vertical flow of CWs can significantly reduce the load of water intake. In the low hydraulic load condition of 0.15m/day, the average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), and total phosphorus (TP) can reach 66.52%, 72.10%, 56.53% and 91.55% in this system, respectively. The influent pool on removal efficiency of pollutants was obviously higher than that of the upper pool, especially in the inlet surface 0-30cm ranges. This research has achieved the effect of using "waste" to treat wastewater, which has strong practical significance and popularization value.

Potential of biochar filters for onsite sewage treatment: Adsorption and biological degradation of pharmaceuticals in laboratory filters with active, inactive and no biofilm

This study investigated the potential of biochar filters as a replacement or complement for sand filters for removal of pharmaceutically active compounds (PhACs) from wastewater in onsite sewage facilities (OSSF). Specifically, the study investigated the effects of biodegradation, adsorption and a combination of these processes on removal of four model PhACs from wastewater in biochar filters operated under hydraulic loading conditions mimicking those found in onsite infiltration beds. Concentrations and removal of the four PhACs (i.e. carbamazepine, metoprolol, ranitidine and caffeine) were investigated over 22weeks in four treatments: biochar (BC) with active or inactive biofilm (BC-active-biofilm, BC-inactive-biofilm), biochar without biofilm (BC-no-biofilm) and sand with active biofilm (Sand-active-biofilm). The adsorption of carbamazepine was high in BC-no-biofilm (99% removal after 22weeks), while biodegradation was very low in Sand-active-biofilm (7% removal after 22weeks). Removal of carbamazepine in BC-active-biofilm was high and stable over the 22weeks (>98%), showing a significant role of biofilm in filter biogeneration. However, carbamazepine removal declined over time in BC-inactive-biofilm, from 99% in week 13 to 73% in week 22. Metoprolol was poorly degraded in Sand-active-biofilm (37% after 22weeks), while adsorption seemed to be the major pathway for removal of metoprolol in biochar. Ranitidine and caffeine were efficiently removed by either adsorption (97% and 98%, respectively, after 22weeks) or biodegradation (99% and >99%, respectively, after 22weeks). In conclusion, biochar is a promising filter medium for OSSF, especially for persistent PhACs such as carbamazepine and metoprolol.

Phosphorus removal efficiency from wastewater under different loading conditions using sand biofilters augmented with biochar

Treated wastewater is a valuable resource, particularly in countries facing water shortage such as Jordan. Nevertheless, excess nutrients, especially phosphorus, may have detrimental impacts on receiving waterbodies. Treated wastewater in Jordan often exceeds the recommended levels set by the Jordanian Standards for wastewater reuse and discharge. Therefore, it is important to reduce phosphorus loads to acceptable levels before discharge. Biofiltration is a low-cost technology that has shown good potential for wastewater treatment. The performance of biofilters largely depends on the media used. In this study, local sand and sand augmented with biochar prepared from the olive oil processing waste (SBC) were used as filter media for phosphorus removal from clarified secondary treated wastewater. The two media types were tested under different hydraulic and phosphorus loading conditions to simulate shock, flooding, and inundation conditions. The results showed that sand media was more effective in removing phosphorus (90.8 ± 2.6%) than sand amended with biochar (83.3 ± 3.2%). Both media showed resilience under extreme loading conditions. Although phosphorus removal efficiency was negatively affected following the extreme loading events, the observed effects were temporary. The simulated inundation event further showed that the media was able to retain the adsorbed phosphorus. Furthermore, the phosphorus concentration in the effluent remained within the prescribed discharge guidelines at all times.

Nature-based flood protection: The efficiency of vegetated foreshores for reducing wave loads on coastal dikes

This paper analyses the effect of vegetation on wave damping under severe storm conditions, based on a combination of field measurements and numerical modelling. The field measurements of wave attenuation by vegetation were performed on two salt marshes with two representative but contrasting coastal wetland vegetation types: cordgrass (Spartina anglica) and grassweed (Scirpus maritimus). The former is found in salty environments, whereas the latter is found in brackish environments. The measurements have added to the range with the highest water depths and wave heights presented in the literature so far. A numerical wave model (SWAN) has been calibrated and validated using the new field data. It appeared that the model was well capable of reproducing the observed decay in wave height over the salt marsh. The model has been applied to compute the reduction of the incident wave height on a dike for various realistic foreshore configurations and hydraulic loading conditions. Additionally, the efficiency of vegetated foreshores in reducing wave loads on the dike has been investigated, where wave loads were quantified using a computed wave run-up height and wave overtopping discharge. The outcomes show that vegetated foreshores reduce wave loads on coastal dikes significantly, also for the large inundation depths that occur during storms and with the vegetation being in winter state. The effect of the foreshore on the wave loads varies with wave height to water depth ratio on the foreshore. The presence of vegetation on the foreshore extends the range of water depths for which a foreshore can be applied for effective reduction of wave loads, and prevents intense wave breaking on the foreshore to occur. This research demonstrates that vegetated foreshores can be considered as a promising supplement to conventional engineering methods for dike reinforcement.

Performance and characteristics of a nitritation air-lift reactor under long-term HRT shortening

The start-up and subsequent operation of nitritation process was carried out in an airlift reactor (ALR) over 253 days under the HRT shortening condition. The nitrogen loading rate (NLR) of the ALR was finally raised to 4.07 kg m−3d−1 by shortening the HRT from 22.7 to 2.1 h under 350 mg l−1 of influent ammonium. The improvement of removal efficiency and nitrite accumulation to 98.7% and 92.4% elevated the ammonium removal rate (ARR) and nitrite production rate (NPR) to 3.89 and 2.81 kg m−3d−1, respectively. The settling property of the nitritation biomass was improved substantially under the high hydraulic loading condition. Scanning electronic microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were used to evaluate the physicochemical characteristics of the biomass. The attachment of chemical precipitates on biomass surface was an important reason contributing to the enhancement of nitritation performance through increasing the sludge settleability. The taxonomic complexities of microbial communities from phylum to species level were dealt with the high-throughput pyrosequencing of 16S rRNA gene sequence. It was revealed that Lactobacillus, Thermomonas, Ignavibacterium and Aquimonas were the most abundant genera in the biomass. The low abundance of Nitrospira and Candidatus Brocadia confirmed the possible occurrence of nitrite oxidation as well as anammox in the ALR.

A chemo-elastic–plastic model for unsaturated expansive clays

Clays are widely used as sealing materials in various geotechnical and geo-environmental engineering applications. These clays are usually unsaturated and are sensitive to chemical composition of the saturating solutions. During their service period, various mechanical, chemical, and hydraulic loading conditions, usually coupled with each other, can be encountered. It is necessary to use a chemo-elastic–plastic unsaturated model to account for these coupled loading paths and simulate the possible behaviours of these clays in their realistic engineering context. In this paper, based on the thermodynamic framework (Lei et al., 2014) for unsaturated expansive clays, the chemo-elastic–plastic model developed by Loret et al. (2002) for saturated homoionic expansive clays is extended to the general unsaturated case. From a theoretical analysis, it is shown that this model is sufficient to simulate the typical behaviours under various mechanical, chemical, and hydraulic loading conditions. The model is then validated against available experimental data of oedometer tests concerning purely mechanical and mixed chemo-mechanical loadings under controlled matric suction on reconstituted Boom Clay mixed with NaNO3 solution. Reasonably accurate estimates of quantitative responses of these complex coupled geochemical loading paths can be obtained, thus giving us a preliminary insight on chemo-hydro-mechanical coupled behaviours.

Risk assessment and economic appraisal of protection methods for the Tarascon-Arles railway embankment

The coordination of flood management practices and the reduction of flood risk as proposed under the Plan Rhone project has led to a vast program of flood defence modernization and construction in the lower Rhone valley. One key element of the project involves the construction of a new 9km levee structure parallel to an existing railway line between the towns of Tarascon and Arles (Bouches-du-Rhone, France ) on the left bank of the Rhone, which has historically been an obstacle to the propagation of flood flows. The new levee is designed to protect the towns of Arles and Tarascon up to the 10−2 annual probability flood event, after which floodwater will flow over a 5km spillway which will be integrated into the structure. In case of overtopping of the spillway via a spillway structure, floodwater is collected in the space between the two embankments and will subsequently flow towards one of ten newly constructed flood discharge structures, spaced at regular intervals in the railway embankment. The levee will form part of a global system of defence which is designed against flooding on the Rhone with an annual probability of occurrence of 10−3 . In the event of overtopping of the levee, the railway embankment will be subjected to hydraulic loading and is at risk of damage from flood flows. During the detailed design phase of the project, options were explored for optimizing the permanent protection for the railway embankment. Using results from 2D and 3D hydraulic numerical modelling, a detailed risk assessment of the railway embankment was undertaken to evaluate its vulnerability under different hydraulic loading conditions and for different failure mechanisms using various parameters including water depth, hydraulic load, the duration of flood exposure and flow velocity. A comprehensive understanding of the main mechanisms of embankment damage under hydraulic loading (internal/ external erosion, overtopping, rotational failure etc.), existing geotechnical conditions and the railway embankment structure were required to undertake the risk assessment. For each hydraulic loading scenario, a detailed economic appraisal was undertaken for each method of protection involving the evaluation of damages associated with disruption to train services and the associated costs to repair the structure. The final stage of the project involved integrating the economic assessment into a wider reaching multi-criteria analysis including indicators for train security, maintainability and environmental impact aspects. The multi-criteria approach was tested under two management strategies to evaluate the effectiveness of each embankment protection system. This paper outlines how the risk assessment, economic appraisal and management-strategy based multi-criteria approach resulted in a highly optimized system of embankment protection with significant gains in terms of both reduced cost of implementation and environmental enhancement whilst maintaining the high levels of railway security required by SNCF-RESEAU.