Both compute suspended transport in the water column the same way. They differ in how they treat cohesive versus non-cohesive material and how they exchange mass between the water column and the bed. The original module handles the two sediment types with separate processes and a user-defined constant erosion rate per class. SEDZLJ applies a unified treatment across all classes regardless of cohesiveness, using site-specific erosion data. Both are dynamically linked to hydrodynamics.

Suspended sediment concentration is the most often available measurement and on its own it cannot pin down erosion and deposition. At steady state, erosion balances deposition, so the observed concentration can be reproduced by a high erosion rate paired with fast settling, or a low erosion rate paired with slow settling, or any combination between. An infinite number of parameter sets fit the same data.

That matters when you extend a model beyond the period it was calibrated on. A model tuned to reproduce historical concentrations with the wrong erosion and deposition pair will diverge under conditions it hasn’t seen. Determining those quantities from measurement rather than calibration is what makes SEDZLJ predictive rather than descriptive.

[EFDC+] SEDZLJ is regarded as one of the most advanced sediment transport models in the world. Developed by Sandia National Laboratories, it derives erosion rates, critical shear stress, and bulk density directly from sediment core samples tested in the SEDFlume apparatus, giving erosion properties that vary with depth through the core and across your site.

EFDC+ provides significant enhancements and bug fixes compared to the EFDC_SNL version, including improvements to mass balance, hard bottom bypass, and computational efficiency, plus multi-threading for faster run times and extension of SEDZLJ to toxics transport.

EFDC+ simulates any number of size classes of cohesive and non-cohesive sediment, non-cohesive bedload, and bed scour, deposition, and resuspension.

Cohesive material is the harder case, because settling depends on flocculation, particles aggregating into flocs whose settling behavior differs from their components, driven by concentration, ionic environment, and flow shear. Directly simulating floc formation is too costly for operational models, so EFDC+ parameterizes settling velocity in terms of particle size, concentration, and flow, offering four published formulations plus a user-defined constant. Cohesive erosion is likewise represented in both of its physical modes, gradual surface erosion once bed stress exceeds the critical erosion stress, and rapid mass erosion when stress exceeds the bed shear strength at depth.

The bed can be a single layer or multiple layers, with the multi-layer option establishing a time-since-deposition versus vertical position relationship.

[EFDC+] EFDC+ also simulates consolidation of beds containing both cohesive and non-cohesive material in any layer, and bed armoring, which develops as coarse material deposits and finer material erodes away. Armoring is handled through a thin active layer at the bed surface, letting depositing and eroding sediment interact in a discrete layer without disturbing the sediment beneath. The active layer thickens with increasing shear stress, representing deeper penetration of turbulence into the bed.

Bedload transport is available in both modules, with updates to each ensuring mass balance.

[EFDC+] EFDC+ supports bed morphology simulation, with elevation changes at the water column/sediment bed interface incorporated into the hydrodynamic continuity equation. You get seamless morphodynamic simulation without linking to another model, and when vertical layering is active, EFDC+ can re-layer the domain as depths change.