MONITORING AND INVESTIGATION OF INTERMITTENT RIVERS IN BULGARIA

River flows could be defined according to their surface hydrologic stream duration as either perennial or temporary. Normally perennial streams flow throughout the year, while temporary streams lack surface flow for some periods of the year. Temporary streams are classified as intermittent or ephemeral. Intermittent streams flow in some periods as result of snowmelt and eventually elevated groundwater tables during the periods of increased precipitations. Intermittent streams are poorly represented in existing river monitoring programs in Bulgaria and seldom are objects of regular monitoring. Only in several gauging stations exist hydrological time series. Furthermore, intermittent and ephemeral streams are not adequately protected by current legislation and management strategies in Bulgaria and generally are neglected. The authors discuss the climatic, hydrological and soil conditions in different part of the country as the major factors determining their origin and distribution. Covering the whole territory of Bulgaria the authors identify four main types of intermittent streams as: 1) intermittent flows as result of Mediterranean climatic impact located in the southern part of the country; 2) sinking intermittent flows as result of specific geological and soil characteristics, 3) intermittent flows in large karst and loess areas and finally 4) the sinking flows in alluvium depositions mainly along the large mainstreams. Nevertheless, the limited number of gauging stations built up at these rivers some hydrological information is collected and statistical results are presented as duration curves of temporal rivers, hydrographs with seasonal characteristics etc. Intermittent streams have a hydrologic flow regime with very specific characteristics that place them as interact between land and water. Unfortunately, in Bulgaria there are poorly mapped, recognized, and protected but they have a critical influence on the ecological health of networks. There exists a strong need for new approaches to scientifically study, the structure and function of temporal streams. The construction of monitoring network for the regular registration of their hydrological regime is surely the first required step for their future detailed ingestions, use and protection.