Overview

This script post-processes Delft3D-4 accumulated seabed flux output to generate seabed sediment distribution maps. The main workflow implements the Central accumulated sediment flux (ASF) approach: it compresses the flux time series per grain size, combines positive (depositional) and negative (erosional) fluxes, and converts the result into relative grain-size availability and bed-layer fractions.

What the code does

• Reads accumulated flux MAT files for multiple grain-size classes and a hydrodynamic grid MAT file (HDF5 / v7.3 format).
• Separates positive and negative fluxes and applies a chosen statistical operator (e.g. mean, percentiles, trimmed mean / ASF).
• Combines positive and negative components according to a selected analysis method (ASF is the default).
• Optionally applies simple shear-stress-based weighting between grain-size classes.
• Normalises the combined flux per cell across grain sizes to obtain:
  • percentage contribution of each size class, and
  • bed-layer fractions suitable as input for morphodynamic models.
• Optionally computes a D50 map from the ASF-based grain-size percentages.
• Writes all outputs as .xyz text files (X Y Z) that can be imported into GIS or plotting software.

Possible exploratory combinations possible

Operation (op) options – time-series statistic per grain size and flux sign (positive = deposition and negative = erosion) for each grid cell

op	Name	Description (per grid cell, per grain, per sign)	Extra input/notes
1	Mean	NaN-aware arithmetic mean of the flux time series	Works for all analyses 1–7
2	95th percentile	95th percentile of flux values
3	Minimum	Minimum flux value
4	Maximum	Maximum flux value
5	Median	Median flux value
6	Trimmed mean (ASF core)	Mean over the interquartile range (25–75 %); returns both trimmed mean and counts N_trim	Needed for ASF when combined with analysis = 6
7	75th percentile	75th percentile of flux values
8	Exceedance mean	Mean of values above the exceed_pct percentile	Uses exceed_pct (default 25 %)
9	BSS-conditioned mean	Mean of flux values at times when BSS exceeds its exceed_pct percentile	Requires BSS file with matching time dimension

For analysis = 7 (CFR), the same op codes are applied to positive/negative flux magnitudes before forming the cumulative flux ratio.

Analysis options – combination of positive/negative fluxes at each grid cell

analysis	Name	Description (per grid cell, per grain)	Special requirements / comments
1	Threshold split	Uses positive statistic for grain sizes ≤ thresh and negative statistic for grain sizes > thresh	Requires thresh and grain sizes on both sides of the threshold
2	Positive only	Uses only the positive (depositional) statistic
3	Negative only	Uses only the negative (erosional, absolute value) statistic
4	Residual depositional flux	Positive − negative; negative values clipped to 0 (emphasises net deposition)	Requires both pos and neg stats (analyses 1–6)
5	Geometric-mean transport	√(pos · neg), with small epsilon; emphasises co-occurrence of deposition and erosion	Requires both pos and neg stats
6	Total transport / ASF	If op = 6 and N_trim available: ASF = μ⁺·N⁺ + μ⁻·N⁻; otherwise total = pos + neg	ASF configuration is op = 6, analysis = 6
7	Cumulative flux ratio (CFR)	Ratio of positive to negative statistics minus 1, i.e. CFR − 1, computed from sign-separated flux fields	Uses only CFR branch in operate_mat (choice = 3)

Recommended combinations

Purpose	Recommended setting	Comment
ASF sediment distribution (default)	op = 6, analysis = 6	Central, frequency-weighted gross exchange per grain
Simple depositional intensity	op = 1,2,5,7, analysis = 2	Deposition (Positive) flux only
Simple erosional intensity	op = 1,2,5,7, analysis = 3	Erosion (Negative) flux only (absolute values)
Net residual deposition	op = 1 or 6, analysis = 4	Highlights areas of persistent deposition
CFR diagnostics	op = 1–9, analysis = 7	Different op give different CFR summaries