Water Discharge and Recharge

[Churchill]

The Guaraní Aquifer, located beneath the surface of Argentina, Brazil, Paraguay and Uruguay, is one of the world's largest aquifer systems and is an important source of fresh water. It has a thickness of about 400 m and contains about 37,000 km³ of water.

What would be the time to completely empty this acquifer in order to provide freshwater to 100 million inhabitants consuming about 200 l/day of water? How much time it would take to recharge this acquifer if rainfall rate is 1000 mm/year over the entire area of the acquifer? Neglect the time it takes water to reach down to the acquifer and assume all rain ends up in this acquifer.

 

[Guest]

You are missing some critical elements to this problem.

1. I noted that you are suggesting that 100 million inhabitants are consuming 200 l/day. Are you serious? There is a discontect between your population figure and consumption rate.

2. In terms of the recovery of water, you haven't mentioned the physical characteristics of the aquifer (e.g. soil matrix/geology, hydraulic conductivity/transmissivity, specific yield, etc.). Unless you are simply going to assume that you can yield enough water to meet the public consumption, then this becomes a trivial math problem based on proportions.

3. Your second question doesn't make much sense since you ask for the time to recharge the aquifer but ask that you neglect time for water to reach down into the aquifer. Again, I am assuming the most sensitive parameter for this estimate is the infiltration rate since simply assuming precipiation (applied water) uniformly distributed over a watershed (area not given) would be proportionality driven by the volume of water in the aquifer. I think you need aquifer characterisitics again and include some of the Soil Water Characterisitic Curve (SWCC) information to adequately determine infiltration.

I hope this helps in terms of re-qualifying your problem.

Regards,

JR