It is simple to connect the geographic position of Zrmanja with the position of mountain Velebit. Zrmanja is many times defined as the south-east border of Velebit. With its spring beneath the peak Poštak and mouth in Novigrad sea, the river is with its 69 kilometers of flow, almost encompassed south-east slopes of this mountain, uniting them in one unit.

From the spring and approximately four kilometers downstream from village Pađane, Zrmanja flows toward the south-east along the road which connects Gračac and Knin. Here it suddenly changes its direction and under Kravlji bridge in a big arc turns toward the west, winding through small karst fields and canyons. It goes through Mokro polje, Ervenik and Žegarsko polje, after which it still goes toward the west, and receives its tributary Krupa. Downstream from Obrovac, Zrmanja gradually turns toward the south-west and runs into Novigrad sea.

The spring of Zrmanja is on 395 m above sea level, and the mouth in Novigrad sea regarding its entire flow of 69 km means it has an average fall of 5,7 m per kilometer.
The basin of Zrmanja is pretty wide. Although the river receives most water from the mountain Poštak, there is significant influence by waters which fall into pits on edges of these fields near Gračac, and come as springs and tributaries which go into Zrmanja.
The average flow of the river Zrmanja in its spring part near Palanka is 5,2 m/sec, and in the lower part of the flow near Jankovića buk upstream from Obrovac 40 m/sec what is influenced by the tributary Krupa and numerous springs.

From the geologic aspect Zrmanja is also very interesting. The basin of Zrmanja is according to geologic researches built mostly of limestone and dolomite. Waterproof rocks are built of limestone from the geologic era of mezozoic, that is trias, jura and crede (220 to 140 million years ago). Waterproof rocks are made of dolomite and limestone plates from the geologic era of jura, and non-waterproof rocks are clastic, made of sandstone, slate, marl and dolomite. As we said before, about 40000 years ago Zrmanja was flowing into Krka.

That means that biggest geological changes occurred in the recent 40000 years. Geologists assume that in the era of 40000 years back to 8000 years ago there was strong erosion which resulted in the creation of todays Zrmanja bed. Today's mouth in Novigrad sea was made by the rise of sea level, which occurred after the latest ice age.