Fetches the DEM (SRTM via AWS Terrain Tiles), fills depressions, computes D8 flow routing, and delineates the watershed, longest flow path, slope and Tc automatically. Click precisely on the stream / valley at your outlet.
Click the map in draw mode to add vertices; Finish Drawing to close. The flow path should run from the hydraulically farthest point to the outlet. Elevations along the flow path are fetched from Open-Meteo to compute slope and Tc automatically.
Catchment Characteristics
NocoDB Persistence
How it works
On first Save/Load the tool finds the WatershedFlood table in NocoDB automatically, creating it if it does not exist (fields: ProjectCode, Title, FullData, UpdatedAt), and fills the table ID above. Saves are scoped by Project Code; the whole project state is stored as JSON in FullData. If automatic setup is blocked by token permissions, create the table manually in NocoDB and paste its ID above.
Rainfall Frequency Analysis
Public-Domain Rainfall Capture (Open-Meteo ERA5)
ERA5 reanalysis (~25 km grid) tends to underestimate short-duration extremes. Use the Gumbel results as a screening estimate and override with IMD Rainfall Atlas / CWC study values in the Design Depth column where available (IMD gridded/atlas values govern for deliverables).
Design Rainfall Depths (Gumbel EV-I)
IDF Coefficients — i = K·Tᵃ/(t+b)ⁿ (i in cm/hr, t in hr)
The IDF relation shapes the storm's temporal pattern (alternating block). When a design depth is set (Gumbel or IMD override), the pattern is scaled so the storm total equals that depth; otherwise the IDF depth itself is used. Site-specific IMD IDF curves override zonal coefficients where available.
Design Storm — Alternating Block Hyetograph
SCS-CN Runoff & SCS Unit Hydrograph
Loss Model — SCS Curve Number
CN guidance (NRCS NEH / TR-55, typical AMC II)
Land use
HSG A
B
C
D
Row crops, straight row
72
81
88
91
Pasture, fair condition
49
69
79
84
Forest / woods, fair
36
60
73
79
Open scrub / wasteland
49
68
79
84
Residential (~38% imperv.)
61
75
83
87
Industrial (~72% imperv.)
81
88
91
93
Paved / roofs
98
98
98
98
Use area-weighted composite CN for mixed catchments. Source: NRCS NEH Part 630 Ch. 9 / TR-55 (1986).
Unit Hydrograph — SCS Dimensionless (PRF 484)
Kirpich: Tc = 0.01947·L⁰·⁷⁷·S⁻⁰·³⁸⁵ (L in m, S in m/m). UH peak: Qp = 0.208·A·Q/Tp (A km², Q mm, Tp hr); Tp = Δt/2 + 0.6·Tc. Runoff increments convolved with the standard SCS dimensionless UH. Ref: NRCS NEH Part 630 Ch. 16; Chow, Maidment & Mays (1988).
Report & Exports
Run Flood Simulation
Looking for the Flood2D server…
Server address (auto-detected — override only if needed)
The simulation runs on the shared Flood2D server (set up once on the NAS — see DEPLOY_ON_NAS.txt). The tool finds it automatically. No server yet? Click Save Project (JSON) on Tab 1 and drag the file onto RUN_Flood2D.bat. Either way the engine produces flood maps, GIS layers, Excel summary and a draft report chapter (.docx). Start at 90 m; refine to 30 m for final maps.
Hydrology report (this tool)
Data downloads
HEC-RAS 2D boundary data (optional — only when a client/regulator requires HEC-RAS)
Paste these into the HEC-RAS Unsteady Flow Data editor (rain-on-grid precipitation BC, or flow hydrograph at a BC line; set the same interval, e.g. 15MIN). After the HEC-RAS run, hand the plan HDF to RUN_HECRAS_PostProcessor.bat. The in-house simulation doubles as an independent cross-check.