# Hydrology Formulator — Calculations on Water

> Pocket reference for hydrology and civil engineering calculations and formulas. (iPhone/iPad app by Historycentral.com Inc.)

- Source: https://appshunter.io/ios/app/hydrology-formulator/id346512904 (this page in markdown: same URL + `.md`)
- Developer: [Historycentral.com Inc](https://appshunter.io/developer/1744330560)
- Category: Productivity, Education
- Price: Free with in-app purchases (on sale, was $4.99)
- Rating: 5.00/5 from 1 App Store ratings · 5 written reviews indexed
- Age rating: 4+
- Requires: iOS 18.6 · 18 MB
- Languages: American English
- Released: 2009-12-18
- Data updated: 2026-07-15
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/hydrology-formulator/id346512904/reviews.md

## What is Hydrology Formulator?

HYDROLOGY FORMULATOR is the ultimate pocket reference for hydrologists, civil
  engineers, environmental scientists, and students. Packed with 1,000+
  formulas, calculators, and conversions, it covers everything from groundwater
  analysis to stormwater design — all in one powerful app.

  HYDROLOGY CALCULATORS

  Infiltration & Recharge — 17 Calculators
  - Porosity, Green-Ampt Infiltration, Horton Infiltration, Philip Infiltration,
   Holtan's Model, Hydraulic Conductivity, Groundwater Recharge, Mean Pore
  Velocity, Specific Discharge, Volumetric Water Content, and more

  Evaporation & Transpiration — 8 Calculators
  - Penman-Monteith ET0, Blaney-Criddle ET, Thornthwaite PET, Crop
  Evapotranspiration, Saturation Vapor Pressure, Evaporation Rate of Lake,
  Relative Humidity, Potential Evapotranspiration

  Open Channel Flow — 12 Calculators
  - Manning's Equation (SI & US), Chezy Equation, Froude Number, Hydraulic
  Radius, Hydraulic Jump, Critical Depth, Specific Energy, Reynolds Number, and
  more

  Pipe Flow — 7 Calculators
  - Darcy-Weisbach Equation, Hazen-Williams Velocity (SI & US), Reynolds Number,
   Water Hammer Pressure, Continuity Equation, Minor Head Loss

  Stormwater & Watershed — 9 Calculators
  - SCS Curve Number Runoff, SCS Peak Discharge, IDF Rainfall Intensity, Kirpich
   Time of Concentration, Gumbel Extreme Value, Detention Storage Volume,
  Composite Curve Number, and more

  Pumps & Water Supply — 7 Calculators
  - Total Dynamic Head, Water Horsepower, Brake Horsepower, NPSHa, Affinity Laws
   for Flow, Head, and Power

  Weirs & Orifices — 6 Calculators
  - Rectangular Weir (SI & US), V-Notch Weir, Broad-Crested Weir, Orifice Flow,
  Spillway Discharge

  Water Flow — 10 Calculators
  - Water Flow Rate, Velocity of Water, Volume of Water Flow, 90° V-Notch
  calculations, Pipe Total Diameter, and more

  Surface Runoff — 6 Calculators
  - Average Velocity, Runoff, Travel Time, Hourly Rate of Rainfall

  Groundwater — 7 Calculators
  - Darcy's Law, Thiem Equation, Cooper-Jacob Drawdown, Dupuit Well Flow, Radius
   of Influence, Storage Properties

  Soil Pollution — 5 Calculators
  - Groundwater Pore Velocity, Effective Diffusion, Hydrodynamic Dispersion,
  Aquifer Parameter, Variance of Pore Velocity

  River Pollution — 7 Calculators
  - River Oxygen Deficit, Critical Time & Distance for Oxygen Deficit,
  Re-Aeration Constants, Dissolved Oxygen, River Flow, Water Temperature

  Lake Pollution — 4 Calculators
  - Waste Entering, Equilibrium Concentration, Settling Loss Rate, Particle
  Deposition Rate

  Sediment Transport — 4 Calculators
  - Shields Parameter, Bed Shear Stress, Stokes' Law Settling Velocity,
  Meyer-Peter Müller Bedload

  Snow Hydrology — 2 Calculators
  - Snow Water Equivalent, Degree-Day Snowmelt

  Culvert Hydraulics — 2 Calculators
  - Culvert Headwater (Outlet Control), Culvert Outlet Control Head Loss

  Flood Routing
  - Muskingum Routing

  Water Balance
  - Water Balance Equation, Storage Continuity

  Plus: Area Formulas, Pollution Cleanup, and more

  CONVERSIONS & REFERENCE

  Hundreds of built-in conversions across 16 categories including:
  - Liquid Measures, Cubic Measures, Linear Measures, Square Measures
  - Flow Rates, Pressures, Horsepower, BTU, Watts, Power
  - Hydraulic Conversions, Sand-to-Volume, Ft-Lbs
  - 8 Temperature Scales (Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, Newton,
   Delisle, Rømer)
  - Metric Conversions and Fraction Conversions

  KEY FEATURES
  - Save and review past calculations
  - Switch between US (Imperial) and Metric units
  - Clean, intuitive interface designed for field and office use
  - Premium upgrade unlocks Groundwater, Pollution, Sediment Transport, Snow
  Hydrology, Culvert Hydraulics, and Flood Routing calculators

## Key features

- 1,000+ formulas and calculators
- Groundwater analysis tools
- Stormwater design calculations
- Open channel and pipe flow equations
- Water pollution modeling
- Conversions and reference data

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| Pro Version | $3.99 | one-time |


## Recent user reviews (5 of 5)

All indexed reviews: https://appshunter.io/ios/app/hydrology-formulator/id346512904/reviews.md

### 1/5 — PE

*2011-12-24*

Needs to show formulas used in calculations.  If not careful one could get poor results.

### 1/5 — Not very user friendly

*2011-05-13*

Needs a better interface. Formulas should be shown. Text gets cut off on menus. Please update. You can do much better.  No sediment transport equations. Come on!!

### 3/5 — A good tool..but

*2010-09-03*

All sorts of great calculators ...but what's up with the long scrolling to find anything. Some menus would be nice.    Also the words are too big and u can't see most of the description of what your clicking on!! But I give 3 stars cuz it's the only hydrology app!  Please update this sucker...it was 5 bucks!!

### 1/5 — Not quite ready for professional use.

*2010-06-04*

great idea but needs more transparecy in formulas, more useful formulas, recommendations for obscure values (e.g. Vapor pressure), easier use of English units.

### 3/5 — Needed additions

*2010-04-21*

Not a bad start.  How about adding a conversions calculator for hydraulic conductivity that includes cm/s, ft/d, gal/d/ft2, and other commonly used units, and the analogous units for transmissivity.

## Frequently asked questions about Hydrology Formulator

### What is Hydrology Formulator?

Hydrology Formulator is a mobile application designed to serve as a pocket reference for professionals and students in hydrology and civil engineering. It offers over 1,000 formulas, calculators, and conversion tools for various water-related calculations.

### What specific areas of hydrology does Hydrology Formulator cover?

Hydrology Formulator covers a broad spectrum of hydrological topics, including infiltration and recharge, evaporation and transpiration, open channel and pipe flow, stormwater and watershed analysis, pumps and water supply, weirs and orifices, water flow, surface runoff, groundwater, soil and river pollution, lake pollution, sediment transport, snow hydrology, culvert hydraulics, and flood routing.

### Is Hydrology Formulator available on multiple devices?

Yes, Hydrology Formulator is available for both iPhone and iPad devices, making it accessible to a wide range of users on Apple's mobile platform.

### How often is Hydrology Formulator updated?

Hydrology Formulator was last updated on March 22, 2026, indicating a commitment to maintaining and potentially improving the application's content and functionality.

### What is the age rating for Hydrology Formulator?

Hydrology Formulator has an age rating of 4+, making it suitable for a very broad audience, including younger students and professionals alike.

### Does Hydrology Formulator have ads?

No, Hydrology Formulator does not contain advertisements. This allows for an uninterrupted user experience focused solely on the hydrological calculations and tools provided.

### What is the user sentiment for Hydrology Formulator based on ratings?

Hydrology Formulator has received an exceptional rating of 5.0 stars from 1 rating, suggesting a highly positive user experience and satisfaction with the app's utility.

### Is Hydrology Formulator free to use?

Yes, Hydrology Formulator is available for free. This allows users to access its extensive collection of hydrological formulas and calculators without any initial cost.

## Version history (last 5 releases)

### 4.0.2 — 2026-03-22

Minor bug fixes

### 4.0.1 — 2026-03-16

Bug fixes

### 4.0 — 2026-03-08

Totally rewritten code, with dozens of additional formulas

### 3.01 — 2018-04-12

This app has been updated by Apple to display the Apple Watch app icon.

Bug fixes that correct​ data entry on certain size phones

### 3.0 — 2017-10-05

Totally rewritten code and completely new User interface. Native to all size iPhones and iPads.  All formulas are now visible

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All apps by Historycentral.com Inc: https://appshunter.io/developer/1744330560

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-15.*