The surface of the department consists of undulating and well-wooded plains, intersected by numerous valleys, and diversified in the north-east by hilly ground which forms a part of the mountain system of the Ardennes.
Behind the lagoons an undulating plain stretches some 50 m.
The surface is a slightly undulating plain.
The river banks, however, are fringed with trees, and in the more undulating lands the timber belts vary from a few hundreds of yards to 5 or 10 m.