Table of Contents

## How do you size an attenuation tank?

How to size a stormwater attenuation tank

- Geographical location. Where you are located will dictate the amount of rainfall you experience during the year.
- The storm return period.
- Allowance for climate change.
- Catchment area.
- Ground water table level.
- Drainage invert levels.
- Drainage layout drawing.
- Soil infiltration rate.

## How do you calculate the runoff coefficient?

The Rational Formula is expressed as Q = CiA where: Q =Peak rate of runoff in cubic feet per second C =Runoff coefficient, an empirical coefficient representing a relationship between rainfall and runoff.

**How many litres of water comes from roof?**

Roughly speaking, 1 millimetre of rain over 1 square metre of roof equals 1 litre of water. This capacity can be calculated using the following formula: Annual rainfall (in millimetres) x Roof surface area (in square metres) = Roof catchment capacity.

**How do you calculate rainwater harvesting tank?**

For calculation we take the following formula: mean annual rainfall in mm x area in m² x runoff factor = collected rainwater in litres. In our example this means: 450 x 120 x 0.9 = 48 600 litres.

### How do you calculate M5 60?

Find the depth of rainfall from a storm of duration 6 hours and return period 10 years on a catchment of 5 km2 in Sheffield.

- From the FSR maps, the M5-60 minutes rainfall is 20.5mm, and “r” = 0.4.
- Divide 20.5mm by 0.4 to get 51.3mm, which is the M5-2 days rainfall depth.

### How is design storm calculated?

Then the design rainfall intensity is calculated with the equation i = a/( d + b ) using the calculated values for a and b. Finally the design peak storm water runoff rate is calculated using the Rational Method equation, Q = CiA.

**How is runoff depth calculated?**

Simple, straightforward methods of calculating runoff can tell you the amount of water that storms bring to the earth. For a given surface area such as a roof or yard, multiply the area by the inches of rainfall and divide by 231 to obtain the runoff in gallons.

**What is the runoff ratio?**

Runoff ratio is the runoff for each watershed divided by the precipitation for that watershed. It is the proportion of rainfall that does not infiltrate and is not taken up by evapotranspiration, and thus ends up as runoff.

## How do you calculate water in a roof?

Calculating your catchment capacity Roughly speaking, 1 millimetre of rain over 1 square metre of roof equals 1 litre of water. This capacity can be calculated using the following formula: Annual rainfall (in millimetres) x Roof surface area (in square metres) = Roof catchment capacity.

## How do you calculate rainwater in mm?

To calculate how much rainwater can be harvested, multiply your rainfall (mm) by your roof surface area (m2) being used to catch rainwater. The resulting number represents how many litres of water you can expect to collect.

**What does M5 60 mean?**

M5-60 minutes rainfall is the expected depth of rainfall in millimetres (mm) from a storm lasting 60 minutes (1 hour) with a return period of 5 years (hence M5).

**How do you calculate rainwater discharge?**

Storm water Discharge calculations: Using Rational formula i.e. Q=CIA Where Q – is design peak runoff rate m3/hr. I – Rainfall Intensity value in mm/hr. A – Catchment area in Ha.

### What is the purpose of the attenuation system spreadsheet?

This spreadsheet calculates the requirements for a attenuation system and assists the user to design a suitable system. This spreadsheet calculates the requirements for a soakaway system and assists the user to design a suitable system.

### What is the small dam design and construction manual?

SMALL DAM DESIGN AND CONSTRUCTION MANUAL May, 1992 PREFACE This manual has been developed by PFRA specifically for use by its staff in the design and construction of the small dams built under various PFRA water development and conservation programs.

**What are the requirements of a dam engineer?**

A professional engineer, qualified in the area of dam engineering, must conduct a complete review of the design, drawings and specifica- tions, and approve, under signature, all project designs and drawings.

**What is the minimum design flood discharge for a dam?**

The criteria used in this manual provides a minimum Safety of Dam Design Flood (SDDF) of 1:100 or 1:50 depending on reservoir storage and a minimum Operating Spillway Design Flood (OSDF) of 1:2. The design flood discharge for an auxiliary spillway is the difference between the SDDF and the capacity of the operating spillway.