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Full workflow

The typical Runoff Lab NX analysis, from rainfall series to flood hydrograph at a basin outlet section.

Diagram

┌────────────────────┐
│ Station + series   │  annual h_max series for 60′, 3h, 6h, 12h, 24h
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Probabilistic      │  Gumbel / GEV / Pearson III / TCEV
│ analysis           │  → h(T) for T = 5, 10, 50, 100, 200 years
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Rainfall curve     │  log-log fit:  h = a · t^n  for fixed T
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ Hyetograph         │  synthetic (Chicago design storm)
└─────────┬──────────┘
          ▼
┌────────────────────┐
│ SCS-CN hydrograph  │  CN, Tlag, area → Q(t), Q_peak
└────────────────────┘

Each box maps to a side panel in the UI. Data flows downward: change a series, recompute upstream, and everything downstream regenerates.

1. Station and series

In the Station panel enter:

  • Metadata: name, code, basin, municipality / province / region.
  • Coordinates: latitude / longitude + altitude. Used for documentation in the final report.
  • Observation period: start and end year of the historical series.
  • Instrument: type (recording rain gauge, etc.).

Below, for each duration (60′, 3h, 6h, 12h, 24h, or custom) paste the annual maxima in mm. Practical tips:

  • copy from an Excel column and paste into the box — the parser splits on newlines;
  • supports . and , as decimal separator;
  • a duration with fewer than 2 values is excluded from analyses and gets a small "skipped" badge.

2. Probabilistic analyses

In the Analyses panel click Add → pick a family. The 4 supported families:

Family Method When to use
Gumbel Moments, Maximum Likelihood Default in many Italian annuals; simple and well-validated for extremes.
GEV L-moments (Hosking) More flexible than Gumbel; handles heavy tails (catastrophic events).
Pearson III Moments (Foster/Kite) Anglo-Saxon tradition; useful when the series shows marked skewness.
TCEV Levels 0-3, regionalised VA.PI. Italy-only; level 3 fully exploits the VA.PI. regionalisation.

Each analysis computes:

  • distribution parameters;
  • heights \(h(T)\) for standard \(T\) values;
  • KS and χ² goodness-of-fit tests;
  • Q-Q plot observed vs theoretical.

Mathematical detail →

Comparing methods

Add multiple analyses for the same station. The output table puts the h(T) values from each method side-by-side: instant comparison, visual uncertainty discrimination.

3. Rainfall curves

In the Curves panel → Add. Select:

  • the source analysis (e.g. Gumbel-moments — 60′/3h/6h/12h/24h);
  • the return period (T = 5, 10, 50, 100, 200 years or custom).

Log-log fitting returns:

\[ h(t) = a \cdot t^n \qquad i(t) = a \cdot t^{n-1} \]

with \(t\) in hours. The page shows the curve overlaid on the observed points \((d_i, h(d_i, T))\) for visual inspection.

Details →

4. Synthetic hyetographs

In the Hyetographs panel → Add. Select:

  • source curve;
  • event total duration (e.g. 60, 120, 360 min);
  • peak position \(r \in [0, 1]\) (Chicago design storm).

The output is a stepped hyetograph with configurable resolution (default 1 min).

Details →

5. SCS-CN hydrograph

In the Hydrographs panel → Add. Enter:

  • source hyetograph or curve;
  • basin area (km²);
  • Curve Number CN (0-100);
  • lag time Tlag (hours).

The algorithm:

  1. computes initial abstraction \(I_a = 0.2 S\) (with \(S = 25400/\text{CN} - 254\));
  2. derives net rainfall \(P_e = (P - I_a)^2 / (P - I_a + S)\) per timestep;
  3. convolves the sequence with the dimensionless SCS unit hydrograph (triangular shape, peak at 0.375 Tp);
  4. sums → total hydrograph \(Q(t)\) with peak discharge \(Q_p\) and time-to-peak.

Details + CN/Tlag wizards →

6. Export

File → Export PDF report: a single document containing everything:

  • metadata and series;
  • per analysis: parameters, h(T), tests;
  • per curve: \(a\), \(n\), \(R^2\);
  • hyetographs and hydrographs with charts;
  • methodology and standard bibliographic references;
  • cover page with logo and project info.

Save and recovery

  • Ctrl+S → save in the browser (autosave is always on).
  • Ctrl+Shift+S → download a .hgstudy file (portable JSON).
  • Ctrl+O → open a previously saved .hgstudy.
  • If you close the tab with unsaved changes, the browser shows the native "Are you sure you want to leave?" prompt; the session also stays in localStorage and is offered for recovery on next open.