ciao. Ho trovato questi significato sul Picchi, ma solo in contesto _medico_

anastomizzare
vt [V+D] (med) to anastomose, to inosculate.

anastomizzare
v. tr.
· (chir.) Unire in anastomosi.

inosculation = anastomosis
anastomosi
[MED]
1 A surgical communication made between blood vessels, for example, between the portal vein and the inferior vena cava.
2 An opening created by surgery, trauma, or disease between two or more normally separate spaces or organs.
[SCI TEC]
1 The union or intercommunication of parts or branches, such as blood vessels, streams, or leaf veins. Also known as inosculation.
2 A network of parts or branches created by the process of anastomosis.

anastomosi o anastomosi
[vc. dotta, lat. tardo anastomosi(m), nom. anastomosis, dal gr. anastómosis ‘imboccatura’, da anastomóo ‘dare sbocco’, comp. di aná ‘verso’ e stóma ‘bocca’; 1574]
s. f.
1 (chir.) Connessione realizzata chirurgicamente tra strutture anatomiche tubulari tra loro omogenee, come vasi o tratti intestinali, o eterogenee, come l'uretere e il colon.
2 (anat.) Ramo di comunicazione tra tronchi vasali o nervosi principali.

granddictionnaire.com geology
hope it helps

anastodmosed: to unite or connect by anostomosis. This process occur in human body, especially in blood vesse, however even in Hydrology is a term in use.

Best regards,
SCOALB

After doing a little research, I found that in the medical field, the term, "anastomizzato" means "by-pass." The only problem is I don't know if this translation will work for your rivers. You know how rivers start to "meander" and split and then eventually come back together forming a type of island in the middle. (I don't know if I'm helping or not.) Maybe you could use "by-pass channels" or "deviating or deviatory channels." Is "deviatory" a word or did I just make that up?

Ciao,

Kara