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Waterfall Weir Rates (waterfall rocks etc)

NOTE: These do not apply to to manufactured spillways as they have their own predetermined flow rates that are shown on the page of each product

The most important consideration in setting up a waterfall is it's appearance. The volume of water required to achieve different effects, from a robust waterfall to a modest trickle, will depend upon the width of the waterfall lip (weir) or stream and the material that it is constructed from. The chart below will tell you how much water is required per 10 cm of waterfall width to achieve different depths of water over the entire width of the waterfall weir. Once you have calculated the total head of the waterfall, it becomes quite easy to determine which pump to use.

Desired Water Depth |
Required LPH for every10cm of waterfall width |

1mm | 144 |

1.5mm | 216 |

3 mm |
432 |

5 mm |
720 |

7 mm |
1008 |

10 mm |
1440 |

13 mm |
2270 |

20 mm |
2880 |

25 mm |
3600 |

### Example

You have a 1 metre high waterfall (measured from the pond surface), and will have 4 metres of tubing run between the pump and the top of the waterfall. The total head is therefore 1.4 meters. To achieve a 7mm water depth over the width of a 25cm wide waterfall weir, you would require a pump producing 2,520 LPH (1008 LPH per 10cm x 2.5 (25cm total width)) at a total head of 1.4 meters.

## How to Measure Flow Rate

This formula can be used to measure the flow rate of the pump you require.

With a container of known volume (e.g. a 25 litre bucket), measure the period of time in seconds taken to fill the container by the flow that you wish to measure . Then divide 3600 by the number of seconds taken to fill the container and multiply by the volume (litres) of the container. The result will be the flow rate in litres per hour.

Example: It takes 10 seconds to fill a 25 litre bucket.

(3600 divided by 10 seconds) x 25 litres = 9,000 LPH

You can also use this formula to decide how much flow you would like over a waterfall. Simply place a hose at the top of the waterfall and adjust the volume of water until you find the flow that you like. Measure this flow and you will have an idea of the volume required to get the effect you desire.

## For Circulation Purposes (including Fountain Heads)

To maintain a healthy natural pond with no fish, experts recommend circulating the water at least once every two hours. This means that for a pond with an effective volume of 8,000 litres, at least 4000 litres per hour (LPH) must be circulated. Hence a pump capable of pumping 4,000 LPH or more at the total head of your project is required. This is the absolute minimum amount of water that you need to circulate.

## Small & Shallow Ponds (up to 1000 litres approx.)

Due to the special requirements and unique circumstances found in smaller and shallow ponds, including most pre-formed units, we recommend you circulate the effective volume once per hour.

### Example

If the effective volume of your pond is 600 litres, look for a pump that can deliver 600 litres at the total head of your system. If you are pumping up to a waterfall or cascade 70cm above pond surface level, you need to pump 600 litres at 70cm head. The head will be increased by the friction created by the tubing.

## Pump Selection

Sizing a pump for a waterfall or a stream is usually quite simple. The first consideration is that the Effective Pond Volume is circulated at least once every two hours. This would be the minimum flow requirement. The second, and usually the most important consideration, are the characteristics of the waterfall. These include the amount of flow that you wish to see coming over the waterfall and the width of the waterfall.

Please take a moment to review how to calculate the total head requirements for your waterfall or stream.

### Example

Assuming you want to operate a waterfall with a vertical head of 1 metre (vertical distance from pond surface level to top of waterfall) and you will have 3 metres of 20mm tubing between the pump and the top of the waterfall. Your total head will be 1.3 metres. The smallest pump that you should consider would be one that is capable of circulating half the effective volume of the pond at a total head of 1.3 metres. Assuming an Effective Pond Volume of 10,000 litres, the pump that you choose will have to be able to deliver 5,000 litres per hour at a 1.3 metres head. This is the minimum requirement for circulation purposes.

Hint: Place your pump as far away from the waterfall as possible to maximize circulation within the pond.

When operating a waterfall, another important consideration is appearance. Depending on the width of the waterfall lip (weir) or stream and your expectations, half the effective volume may not be adequate.

The next step is to determine the flow requirements of your waterfall to achieve the type of effect you desire. You may need to consult the waterfall weir chart for more details.

**Hint**: As a rule of thumb, 380 LPH per 25mm of waterfall/stream width will provide a good flow equal to a sheet of water approx. 9mm deep over a waterfall weir.

## Example

Assuming the waterfall is 45cm wide and using the 380 LPH per 25mm guideline, you should select a pump that can deliver at least 6,840 LPH (380 LPH x 45cm width) at a 1.3 metres head (as calculated above). This is slightly more than the 5,000 LPH that the 10,000 litre pond in our example requires for circulation purposes alone but will result in a more aesthetically pleasing display. Within reason, circulating the effective volume of the pond more frequently will not harm the pond.

Once you have determined the volume of water that you will require, visit our online store and you can search our pond pump range by flow rates. In this example you would look for a pump in the 8000 LPH max. output range because you require 6,840 LPH at a 1.3 metres total head.

The final selection is up to you. Criteria would be initial cost, power consumption and manufacturer's warranty. The annual operating cost comparison figures on pond supplies website make it easy to determine which pump will be most economical to operate over the long term. Sometimes, a less expensive pump with a high power consumption will cost you more in the end.

**Hint**: Make sure your lower pond is large enough to accommodate the flow from your waterfall and the output from the pump . This will ensure an adequate water supply for the pump at all times and helps contain any splash that the waterfall may cause.

If a flow rate of half the Effective Pond Volume once every 2 hours is too much for your waterfall, we recommend to split the flow coming from the pump discharge by using a hose tee, and diverting part of the flow to another water feature or to the other side of the pond to maximize circulation. You may have to install a ball valve in one or both of the lines to control the amount of water going in each direction.

All that is left to do is to choose the correct size of tubing as dictated by the maximum flow rate of the pump you select. Recommended tubing sizes are listed for each pump that we sell. As each pump has different requirements, the tubing flow rate chart is meant as a guideline only.

**Hint**: If your pump does not deliver the amount of water it is rated for, perhaps you are using the wrong size tubing.

### Progress

Actual Pond Volume

Maximum pumping height

Waterfalls, streams and tube friction loss

The weir rate for waterfalls and streams

Water filter (if being used)

## Choosing a pond filter

How to choose a pond filter >> NEXT >>