Accordingly, these precipitations generate average runoff modules varying between 5 and 15 1/s/km2. In the highest parts of the Kotel Balkan, rainfall reaches more than 750-800 mm and the runoff module up to 10 1/s/km . In the low'er parts of the Kamchia valley precipitation falls to 550 mm per year, and the runoff module drops to 2 1/s/km2 on the Kamchia River and to 1-2 1/s/km2 on the Great Kamchia River.