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Paris Manuscript F — 87

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Bibliothèque de l'Institut de France, Paris

Figura di stagno presso al mare, con:

stagno - mare1

Perché li stagni son generati presso al mare e perché le lor gran dilatazioni versano in mare per sì stretto canale, dai lati del quale è fatto2 sì grande argine in fra sé e 'l mare?

Le fortune3 del mare gittano a riva gran quantità di rena, la qual s'inalza per tutta essa riva, così sopra la bocca dello stagno come altrove e, cessato la fortuna, la bocca dello stagno riman chiusa della predetta materia gittata dal mare, e l'acqua che lo stagno riceve da' circunstanti fiumi, non trovando più esito, si va inalzando e acquistando peso e potenzia; e così o rompe l'argine interposta in fra sé e il mare, o ella trabocca di sopra e col suo versamento consuma tanto di tale argine, quanto essa tocca; e tanto persevera tal corso, che ella sgombera4 dinanzi a sé tutta quella materia, che proibiva il suo necessario isgombramento. E d'altro non consuma se non tanto quanto bisogna; e nel principio allarga assai, perché l'acqua che versa sopra la c[hi]usa5 della bocca, è sottile; e nel fine si ristrigne il corso di tale acqua, perché tal corso s'è fatto più grosso per l'acquistata profondità; e quest'è la causa che tale uscita delli stagni in mare sempre è stretta.

Figure of a lagoon near the sea, with:

lagoon — sea. Why are lagoons formed near the sea, and why do their broad expanses pour into the sea through so narrow a channel, on whose sides so great a bank is raised between the lagoon and the sea? The storms of the sea cast onto the shore a great quantity of sand, which rises along the whole shore, over the mouth of the lagoon as elsewhere; and once the storm has ceased, the mouth of the lagoon stays closed by that material thrown up by the sea. The water the lagoon receives from the surrounding rivers, finding no outlet, rises and gains weight and power; and so it either breaks the bank set between it and the sea, or it brims over the top and by its overflow eats away as much of that bank as it touches. Such a course keeps on until it clears away before it all the material that blocked its needed discharge, consuming no more than is necessary. At the beginning it widens greatly, because the water pouring over the closed mouth is shallow; and at the end the course narrows, because it has grown deeper through the depth it has gained; and this is why the outlet of lagoons into the sea is always narrow.

Why a lagoon drains to the sea through a narrow channel

Sea storms seal the lagoon mouth with sand until the pent-up water breaks through

Hydraulics Geology

This folio explains the formation and drainage of coastal lagoons. Sea storms throw sand along the shore and seal the lagoon's mouth; the rivers feeding the lagoon then raise its water until it breaks or overtops the sand bar. The escaping water scours away only as much material as it must, widening at first over the shallow lip and narrowing as its channel deepens. A small landscape sketch labels the lagoon (stagno) and the sea (mare).

On this page

Why lagoons empty to the sea through a narrow outlet

Leonardo asks why lagoons form beside the sea and empty into it only through a narrow channel walled by high banks. The pent-up river water, finding no exit, rises until it breaks or overtops the sand bar, then scours a course no wider than it needs, narrowing as the channel deepens.

Storm-driven sand closes the lagoon mouth

Storms hurl a great quantity of sand along the whole shore, and when they cease the deposited sand seals the mouth of the lagoon. The trapped water then gains weight and power and eventually carves its outlet through the bar.

Reader's Edition — described with AI from the e-Leo transcription.