[GRASS-user] agricultural small water reservoir

[Rich Shepard]

On Wed, 26 Jul 2023, bonushenricus wrote:

> This is a question on the approach to take in order to achieve a
> consultancy objective. For two farms I have to give some input on the
> possible design of a small water reservoir for agricultural use. I have
> this rainfall data: the number of days per month of moderate rainfall (4-6
> mm/hr) of at least 4 hours. So, without taking into account extreme
> events, which are more interesting for erosion, I was thinking of doing a
> r.sim.water calculation for each month of the water depth in the
> reservoirs, and at the same time an evaporation calculation, to build up a
> yearly report of the potential changes in the amount of water available.
> Has anyone ever used GRASS for this type of work? Perhaps for dams?

Enrico,

There are a couple of methods used in the US that might be applicable, but I
suggest you look at precipitation records for the past few years in the
region of the two farms. Given the rate of climate heating and the more
frequent strong weather events everywhere any existing ag pond sizing method
is probably no longer valid.

Depending on the purpose of the pond I would find the most extreme
precipitation events (and the antecedent weather conditions) and add a
safety factor to those. It would be better to oversize them (if that could
be done) than have them overfilled.

It's a changed world and we're all guessing how to advise clients to be
prepared for unpredictable, extreme events.

Good luck,

Rich