A HydroCAD alternative for stormwater design in the browser

What HydroCAD is and who it suits

HydroCAD is a stormwater modelling program from HydroCAD Software Solutions LLC, sold since 1986. A model is a routing diagram of nodes: subcatchments that generate runoff, reaches and ponds that route it, and links that bring in a hydrograph from elsewhere. Runoff can come from SCS/NRCS methods, SBUH or the Rational Method, and the vendor describes it as ideal for studies using TR-20, TR-55 or SBUH. Each pond can carry any number of outlet devices such as weirs, culverts and standpipes; ponds can be coupled with automatic tailwater; and the program handles pumps, float valves, progressive dam breach, underground storage chambers, pollutant loading and watershed import from CAD.

It runs on Windows. The current version is HydroCAD 10.2, whose Release 9a added AutoCAD 2027 support. Pricing scales with node capacity: a permanent licence costs USD 295 for 5 nodes and up to USD 2 395, the 20-node system costs USD 895 permanent or USD 375 a year, and annual licences start at USD 195 (hydrocad.net, 8 October 2026). A licence allows one simultaneous user on any number of the organisation’s computers, and a free Sampler handles up to 5 nodes in 60-minute sessions.

HydroCAD suits US site-development drainage: post-development detention, underground chamber systems, and permit submissions built on TR-20 and TR-55.

Where HydroCAD is the better choice

• A linked model. One HydroCAD diagram carries runoff from several subcatchments through reaches and ponds to an outfall, re-routing everything when one input changes. Studio’s tools each handle one element. Flood Routing routes one storage element; a cascade of basins has to be routed pond by pond, carrying each outflow hydrograph to the next by hand.
• Coupled ponds and tailwater. HydroCAD couples ponds and computes tailwater automatically. Studio’s weirs assume free discharge with no submergence correction, and nothing in Studio passes a downstream pond level back upstream.
• Hydrographs per subcatchment. HydroCAD generates a TR-20 or SBUH hydrograph for each subcatchment. Studio’s TR-55 calculator is the graphical peak discharge method and returns a peak only. Studio’s Hydrograph Generator shapes a hydrograph around a peak you supply; it does not generate runoff from rainfall.
• Products and add-ons. Built-in chamber definitions from storage manufacturers, pumps and float valves, dam breach, pollutant loading and AutoCAD or BricsCAD import have no Studio equivalent.
• Many storms in one run. HydroCAD manages and reports several rainfall events together. In Studio each return period is a separate routing, and the basin auto-size targets one event at a time.

Where Delta Hydro Studio differs

No install, no node limits. Studio runs in a browser and its price does not depend on model size. The free Stream plan keeps five saved calculations per tool with watermarked reports; River and the per-seat Delta team plan remove those limits.

TR-55 peak discharge. The TR-55 calculator runs the graphical peak discharge method from TR-55 Chapter 4: enter sub-areas and it builds an area-weighted composite curve number, applies the four NRCS rainfall distributions (Types I, IA, II and III), the pond and swamp factor, and checks Tc against its 0.1 to 10 hour range and Ia/P against 0.10 to 0.50. Each input takes SI or US customary units.

Time of concentration with the TR-55 segments. The time of concentration calculator has the segmented sheet, shallow concentrated and channel flow method HydroCAD users know from its flow segments, alongside Kirpich, the NRCS lag equation, FAA, Kerby and the SCS-SA method.

A large storm library. The design storm generator builds hyetographs from about 390 temporal patterns covering 136 countries, including the NRCS types, Huff quartiles, the Chicago storm and alternating block, in millimetres or inches. Storms export as CSV, an EPA SWMM rainfall file or an HEC-HMS gage file. Depths can come from Design Rainfall: NOAA Atlas 14 for the US, BoM IFD for Australia and the K5_1060 grid for South Africa.

Pond routing with real outlets. The detention pond calculator routes an inflow hydrograph by modified Puls (storage indication). The basin is defined by its shape (rectangular, trapezoidal or circular, with side slopes), an elevation-volume table or an elevation-area table, and tables can be pasted in. Outlets combine in parallel: sharp-crested, V-notch, broad-crested and Cipolletti weirs, standpipes and risers, culverts and known stage-discharge tables. Culverts use the same FHWA HDS-5 inlet- and outlet-control hydraulics as Studio’s Culvert Designer and can be imported from a saved culvert design. Auto-size finds the basin volume that holds peak outflow to your target. The same tool routes channel reaches with Muskingum or Muskingum-Cunge.

One workspace. A TR-55 peak, a culvert design and a riprap apron live in the same project, values move between tools with Send to, and each of these tools exports Word and Excel reports. Teams on the Delta plan share projects.

HydroCAD and Studio side by side

How to move a job across

1. Catchment. For each HydroCAD subcatchment, carry the area and the sub-areas with their curve numbers into the TR-55 calculator; it composites them the same way.
2. Tc. Re-enter HydroCAD’s flow segments as sheet, shallow concentrated and channel segments in the Tc calculator, then send Tc across.
3. Storm. Use the same 24-hour depth and NRCS distribution type. If you need the hyetograph itself, build it in the design storm generator.
4. Inflow hydrograph. TR-55 gives a peak, not a hydrograph. Paste the inflow table (time in minutes, flow in m³/s) from HydroCAD’s report or another model into Flood Routing.
5. Pond. Paste HydroCAD’s stage-storage table as an elevation-volume table, then add each outlet device with its crest or invert on the same datum as the basin. For a culvert outlet, analyse it first in the Culvert Designer and import the saved design.
6. Several ponds. Route the upstream pond, export its outflow table as CSV, and paste it as the next pond’s inflow. If the ponds interact through tailwater, keep that model in HydroCAD.
7. Compare one event (peak outflow, maximum water level and storage) before relying on the Studio version.

Where to start

Start with the TR-55 calculator and the time of concentration calculator for peak flows, the design storm generator for hyetographs, and the detention pond calculator for routing and outlet sizing.