How is the maximum harvestable right dam capacity calculated?
The maximum harvestable right dam capacity (MHRDC) for a landholding is calculated using the WaterNSW Maximum Harvestable Rights Dam Capacity Calculator. The MHRDC is based on the size and location of a landholding. A harvestable rights multiplier is applied to each landholding. It varies across the state as it considers factors such as regional evaporation, rainfall rates and patterns and assumed demands on harvestable rights dams.
How do I determine the capacity of existing harvestable rights dams on my landholding?
An important part of determining a landholder’s ability to construct new dams or enlarge existing dams is the estimation of the capacity of dams currently on a landholding.
The instructions below provide a simple method to estimate dam capacity. If any of the dams are greater than 10 megalitres in capacity, then you will need to do a more accurate calculation to determine the dam’s capacity.
If you require further assistance with these calculations, please contact WaterNSW on 1300 662 077 or Customer.Helpdesk@waternsw.com.au in the first instance.
- Decide the shape of the dam from the options above.
- Measure the relevant width and length at top water level and record these numbers. All dimensions need to be recorded in metres.
- Measure the maximum depth of the dam and record this number.
- Use the formula relevant to the dam shape above to calculate surface area in square metres of each dam and record the results.
- Using the following formula for all dam shapes, calculate the volume in cubic metres.
Volume = 0.4 x Surface Area x Depth Record the results.
Note: The conversion factor of 0.4 considers the slope of the sides of dams.
- Divide this volume by 1000 to convert cubic metres to megalitres. This is the dam capacity in megalitres (ML).
If you have existing dams on your landholding that are mixed-rights dams (that is, they capture rainfall runoff under the harvestable right but also store other water lawfully taken from a water source), then you will need to contact WaterNSW to get assistance with calculating the harvestable rights volume within the dam.
Does my maximum harvestable rights dam capacity change if I subdivide or sell part of my property?
Because the maximum harvestable right dam capacity (MHRDC) is directly related to the size of your landholding, when you subdivide or sell part of your landholding, your MHRDC is reduced proportionally. For example, if you sell half of your landholding, your MHRDC is halved.
If your landholding is being subdivided, then some of the resultant smaller landholdings may have dams that are greater than the revised MHRDC for that new landholding size. You will need to reduce the size of those dams or apply for works approvals for the dams and obtain a water access licence for the volume of water that exceeds the revised MHDRC. There is no guarantee that the licence or approval will be issued.
It is recommended that you contact WaterNSW before finalising plans for subdividing or selling part of your landholding.
Do I have to measure or meter harvestable rights water?
No, harvestable rights water use does not need to be measured. Each landholding has a maximum harvestable right dam capacity (MHRDC) which represents a percentage of rainfall runoff. The MHRDC is the volume of water that can be legally captured and stored on a landholding under harvestable rights. If a harvestable rights dam is constructed within the limits and the water captured by the dam is used in accordance with the harvestable rights rules, then there is no constraint on the number of times the dam can be emptied and refilled by rainfall runoff and no requirement for water taken by the dam to be recorded and reported.