README.md

stormsewer

Storm sewer hydrology and hydraulics for Python: Rational method, Manning, standard-step HGL/EGL backwater, and HEC-22 inlets. The same Rust engine that powers the StormSewer desktop app, exposed as a native extension — no Python dependencies, no server.

pip install stormsewer

Primitives

Float in, float out. Useful for replacing a spreadsheet column.

import stormsewer as ss

ss.intensity(60, 10, 0.8, 12)          # IDF: i = a/(t+b)^c  ->  5.0607 in/hr
ss.rational_q(0.70, 5.0607, 1.0)       # Q = C i A           ->  3.5425 cfs
ss.manning_capacity(1.25, 0.013, 0.005)  # just-full capacity ->  4.5801 cfs
ss.normal_depth(3.5425, 1.25, 0.013, 0.005)  # -> 0.8254 ft (None if it won't fit)
ss.critical_depth(3.5425, 1.25)
ss.circular_geometry(1.25, 0.8254)
# {'area': 0.8597, 'wetted_perimeter': ..., 'hydraulic_radius': ..., 'top_width': ...}

Pass si=True for metric: the Manning factor becomes 1.0 and g becomes 9.81.

ss.manning_capacity(0.4, 0.013, 0.005, si=True)   # m3/s

Whole networks

import stormsewer as ss
import pandas as pd

result = ss.analyze_project(ss.demo_project_json())

pipes = pd.DataFrame(result["pipes"])
print(pipes[["id", "design_q", "capacity", "pct_full", "velocity", "hgl_up"]])

nodes = pd.DataFrame(result["nodes"])
print(nodes[nodes.floods])          # anything surcharging to the surface

analyze_file("project.ssproj") reads a file saved by the desktop app, and analyze_ssn(text) takes the plain-text network format:

ss.analyze_ssn("""
IDF        60 10 0.8
TAILWATER  100.5
MINTC      10

NODE N1   inlet    0    0  104.0  110.0  1.0  0.70  12
NODE OUT  outfall  300  0  102.5  108.5

PIPE P1   N1  OUT  300  1.25  0.013
""")

Each pipe dict carries id, from, to, slope, total_ca, tc, travel_time, intensity, design_q, capacity, pct_full, velocity, normal_depth, critical_depth, hgl_up, hgl_dn, and surcharged. Each node dict carries id, tc, rim, hgl, freeboard, and floods.

Constants

K_MANNING_US (1.49), K_MANNING_SI (1.0), G_US (32.2), G_SI (9.81).

StormSewer uses K = 1.49, matching FHWA HDS-5 and HEC-22 rather than the 1.486 some spreadsheets use — a 0.27% difference in capacity. See VALIDATION.md, which works every number on a reference network by hand.

What this is not

It computes the published equations; it does not decide whether the Rational method suits your site, what C to use, or which storm to design for. Those stay with the engineer sealing the drawing.

License

GPL-3.0-or-later, like the rest of StormSewer.