Hello,

To me the "sustainable yield" of an aquifer refers to its recharge whereas the "safe yield" refers to a lower value than recharge and the is determined on parameters (economical and ecological) that define what would be a "healthy aquifer". I however agree that this definition my not be consensual.

Romain Chesnaux I think they both refer to the safe and fair yield/exploitation rate. I have been using them interchangeably by the way. And, When I use them, I was refer to "the rate of groundwater that I can exploit from an aquifer without affecting the sustainability/future use of the aquifer system". However, I can see on the wider literature that the terms are still debatable. So, The first thing I want to ask is their similarity. Are they similar or not? Secondly, do they have differences?

"sustainable yield" = recharge = maximum quantity of water that can be supplied by the aquifer without depletion

"safe yield" = quantity of water lower than recharge and that can be supplied by the aquifer in a safe way

So, "safe yield" is lower than "sustainable yield" and even though the definitions look similar in terms of quantity of water that can be exploited, their respective values are different.

Romain Chesnaux

Great. Thanks for the clear definitions of the terms. But, does this mean that "safe yield" is a random number/amount which is lower than sustainable yield? Can you estimate an exact number for "safe yield"? How? As per your definitions, sustainable yield can be estimated as far as you estimate the recharge. But, is there anyway to estimate any exact number/amount for safe yield? Or you just say it as "any rate of exploitation which is less than sustainable yield"?

Yes "Safe yield" is lower than "Sustainable yield" and safe yield is indeed "any rate of exploitation which is less than sustainable yield".

Sincerely

Article Eco-Hydrological Footprint of a River Basin in Western Ghats

Sustainable yield or Safe Yield has to be defined first. Sustainability is a site specific thing. It has nothing to do with recharge. I remember my research group giving the same statement when I started my Phd around this topic which was later retracted by everyone. Go through the water budget myth journals. You define sustainability because any sort of water extraction will effect the flux in the system where the system or an ecological unit has to be defined by you as a hydrogeologist. Try going through journals with topic water budget myth, water sustainability etc.

Ashutosh Singh

I think, sustainable use means exploiting from a system without affecting the system for future use. Water balance should be assured to have a sustainable groundwater resource. What goes out of the system should be equal to what comes in. Otherwise, the storage will be depleted. And, what comes into an aquifer system is recharge. So, I don't think there is anything wrong with defining sustainable yield as it is equal to recharge. In other words, sustainable yield of an aquifer system is the rate that comes into the system (recharge). Can you disprove this one? Ready to hear from you, if you think that my definition is wrong. Romain Chesnaux stated it well by the way. I am convinced by his statements above. So, please prove us wrong, if you have solid evidence.

Yes! I can disprove this theory. What comes in is recharge which feeds the streams and other lakes of ecological value. Even if that is not the case the water flows outside the boundary. So whenever you take out any water, for a transient period the water may come from the storage. Now take the Theis model into account which states that the cone of depression due to pumping continues to increase till the water from the storage is depleted and then the water from the boundaries of the cone of depression starts coming(consider the steady state groundwater flow equation). So what you can extract from a system is the recharge minus the flux lost to streams and lakes which is zero. So lets say that you cannot extract at all any water because of mass balance.

Now the amount you extract will be the amount which was used to feed the lakes and river. Now a water manager/hydrogeologist has to defined that how much reduction of baseflow to a river or lake can be accepted as sustainable. Now this is what sustainability is all about.

Sustainable yield is touse water our need and to save water for feature

Safe yield is we can use water for our need with less quantities at present only not for feature