The hydrographic network is mainly supplied with water coming from precipitations and from small rivers with little flow. Luncavita and Jijila Valleys developed on synclinal lines, while part of Taita Valley developed on a fault line. Luncavita, Jijila and Taita belong to the Dobrudjan short rivers group. Because the rivers’ water results in most cases from precipitations (only to a small extent they result from snow or come from underground source), the flow is characterized by big variations, which is a consequence of the continental aspect of the climate. The water courses belong to the Danube hydrographic basin (Jijila, Luncaviţa, Cerna, Sorniac rivers) and to the Black Sea hydrographic basin (Taiţa River). Due to the dry climate, the water flows are reduced in quantity, most of them having a seasonal character. Temporary waterflows are forming on the rocky valleys, during the rainy seasons, especially in spring.