Ground water rechard

From the InVEST model diagram, it mentioned the ground water rechard. But in the text I did not find clear explanation whether the Water Yield excludes the ground water rechard.

I expect the result of the water yield = precipitation - (evaporation, transpiration) - ground water discharge

But from the input layers and the text, it's still not clear if and how the odel exclude the ground water discharge.

Any explanation is highly appreciated.

Viet Anh



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Comments

  • swolnyswolny Member, NatCap Staff
    Hello Viet Anh -

    In the Seasonal Water Yield model, there are two main properties calculated, quick flow and a baseflow index. Monthly "quick flow" is calculated first. This is the precipitation that runs off of the landscape very quickly, and does not infiltrate, so cannot contribute to baseflow. 

    Now, the amount of water that is not quick flow is available to infiltrate, and it can contribute to recharge. This is calculated using equation 3 in the User Guide:  Li=Pi−QFi−AETi. 

    So the model works a little differently than you expect. There is not a single "water yield" result that combines quick flow and base flow, but two results that show the places on the landscape that contribute to these separately. 

    Does this help?

    ~ Stacie
  • Dear Swolny/ Stacie,

    Thanks for your suggestion, it help a lot. I think the advantage of InVEST is that it's more simple and can be used by none-hydrology people.

    For the people with less background in water modelling, I think this kind of conceptual summary is important. I would love to have an additional diagram that explains the quick flow and base flow as you said.

    Thanks

    Viet Anh
  • @Rich: yes this was what I looking for. Thanks a lot.

    I work with the "Water Yield: Reservoir Hydropower Production" which doesn't have this explanation.

    Btw, I noted that the Seasonal Water Yield require a DEM as input while Reservoir Hydropower Production was not. Could you share some inside while the hydropower water yield does not require DEM.
  • RichRich Administrator, NatCap Staff
    Hi @hoangvietanh, sorry, I hadn't realized you're using the reservoir hydropower model. The figure nor user's guide I sent is relevant in this case. Note the hydropower production models does not route water nor consider ground water recharge so no DEM is needed in that case.
  • Hello @Rich,

    Thanks for your kindly follow up with my question. 

    In the diagram (in my 1st question) taken from the Hydro-power model, it also mentioned "groundwater recharge". In this case should I understand that the water yield also include ground water recharge.

    If we consider a large watershed will groundwater recharge make any different to the hydro-power production or we assume that all water remained (after evaporation, transpiration) will eventually contribute to hydropower.

    Thanks
  • swolnyswolny Member, NatCap Staff
    The Annual Water Yield model does not differentiate between surface and sub-surface flow, and it specifically does not quantify groundwater recharge. The diagram shows a water balance, and indicates that some precipitation runs off into streams through surface/sub-surface flow (which is what the model includes) and what doesn't run off becomes groundwater (which the model does not include.) 

    So, the model calculates hydropower production only from the surface/sub-surface water that runs off into streams, not including groundwater.

    ~ Stacie
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