H - Revised Integrated Water Management Plan by Cardno (inc MUSIC file) (13.09.19)

4.2 Water Balance Tool
   4.2.1 Model Objectives
   The overall objective of the water balance is to test the performance of the designed Strataflow system with respect to
   the likely water requirements and behaviour of the proposed tree. Specifically, the water balance aims to:
     • Determine the water storage behaviour of the tree pit
     • Assess the water availability of the designed configuration, comparing a WSUD tree with a traditional tree pit
     • Predict the health of the tree using a wilting point as the threshold at which the tree is likely to fail
     • Evaluate the sensitivity of the proposed configuration to varied parameters (eg size of diverted catchment, size of
       the tree, high water consumer vs low water consumer, soil properties, irrigation input)
     • Inform design. For example, will a larger tree spacing be required, such that more stormwater is diverted into the
       tree pit to enable survival? Will a smaller tree be more suitable? Will a native tree be more suitable?

   4.2.2 Performance Indicators
   If there is not enough water, the tree will suffer and wilt. As such the system should be assessed based on whether
   the defined wilting point threshold is reached. If the soil moisture (represented as a percentage of field capacity) drops
   below this threshold. Parameters should be changed under the ‘optimisation’ phase of the modelling (refer Appendix
   D), to bring the soil moisture above this threshold.
   On the flip side, if there is too much water, the tree can become water logged and suffer.

   4.2.3 Model Variables
   The interface, as shown on Figure 6, depicts the variables that can be input and adjusted to simulate site specific
   conditions. The subsequent chart summarises the general procedure to adjust these inputs and undertake the
   modelling.
   A detailed step by step guide is provided in Appendix D.




   Figure 7 – Tree Water Balance User Interface


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