In the first chapter of Lingua Latina per se Ilustrata, there are a series of sentences used to teach the usage of two adjectives, magnus and parvus. For example:
Nīlus fluvius magnus est. Tiberis nōn est fluvius magnus, Tiberis fluvius parvus est. (22–23)
Sicilia īnsula magna est. Melita est īnsula parva. (29)
The context for these sentences is a map that clearly shows the relative sizes of islands, and the relative lengths of rivers. Thus it seems that here parvus and magnus are being used to communicate both ideas. But in English, a "big river" to me is one that is primarily wide or deep, not so much long. Similarly a "small river" is usually easy to cross, but not necessarily short.
My question, then, is, do parvus and magnus strongly indicate the length of a river? Are they suitable adjectives when clarity in this sense is needed? Or for the elimination of ambiguity is it necessary to use other adjectives, like longus and brevis?
My dictionaries don't help me much: Traupman begins his entry on parvus with "small, little, puny; short; young," but on the same word Cassell doesn't mention "short" except in relation to time.