Routing of waterbodies into the model

[Swetasree Nag]

Dear SWAT+ User,

I am working on a SWAT+ model where my study area includes over 900 waterbodies (reservoirs, lakes, ponds, etc.). I seek your guidance on the following points to ensure proper representation and routing of these waterbodies:

1. The SWAT+ manual mentions that reservoirs should be located on streams. However, many of my waterbodies are not directly on streams. How can I incorporate these into the model? If I initially define them as wetlands, and later change their hydrology type to reservoir using the SWAT+ Editor (while manually assigning an outlet), will this approach work effectively? If not, could you kindly suggest an alternative?

   To address this, I have generated streams at a finer resolution to connect as many waterbodies as possible. However, some waterbodies still remain unconnected. At what lowest threshold can streams be generated in SWAT+ to reasonably represent flow paths? I understand that using a finer threshold may produce streams that do not exactly match real-world conditions but could still serve as flow paths. Please correct me if I am wrong or if there is a better approach.

2. For accurate routing and interaction between waterbodies, would a grid version of SWAT+ be more suitable than a non-grid setup? I understand that in the grid model, routing occurs between neighboring cells, allowing upslope and downslope interactions. I would appreciate your suggestion on which approach would be better in this scenario.

3. For waterbodies not located on streams, if I manually define outflow, can these contribute to the aquifer or corresponding HRU through overland flow when conditions permit? How should I determine and specify such outflow for these cases?

4. Lastly, I would like to understand how SWAT+ calculates the volume of lakes and how it links with overland flow generation.

I look forward to your insights. Thank you for your time and support.

Best regards,
Swetasree Nag

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