Case Studies from the Dinaric Karst of Slovenia

Fig. 19: Canyon of river Cetina with mountain Mosor in the background (photo: A. Mihevc).Seawater usually underlies fresh water on theislands, resulting in lenses of fresh water belowsurface. The interface between fresh andsalt water along the Adriatic coast is morecomplex due to different patterns of inflow offresh water (superficial or underwater), differentdischarge and different geometry ofconduits. On the western peninsula Istra (Istria),below the mountains Učka, Velebit, Biokovo,in Stonski zaljev (Ston Bay) and in thebay of Boka-Kotorska, examples of submarinesprings, also called “vruljas”, are numerousand efficacious. In some cases water is mixed(i.e., brackish), which presents a problem forwater supply, especially in summer when dischargesare the lowest. A lot of coastal springsare located above sea level and discharge freshwater – the biggest ones are Timavo/Timava(Q min= 9 m 3 /s, Q avg= 30.2 m 3 /s, Q max= 138 m 3 /s;Ford & Williams 2007 after Smart & Worthington2000) and Ombla spring, near Dubrovnik,with a natural average discharge of 33.8 m 3 /s(after 1965, the average discharge was reducedto 29.6 m 3 /s due to the construction of a hydroelectricplant in the hinterland; Milanović2006). Parsts of the hinterland along coast risesteeply to Učka, Velebit, Biokovo and Orjen,but in many cases shallow karst is developedin areas with little topographic relief (e.g., Istra,Sjevernodalmatinska zaravan (North Dalmatianplain), Ravni kotari). A similar situationoccurs on the continental leveled surface betweenrivers Kupa/Kolpa and Una. Homogeneityof such karst is often interrupted with beltsof Eocene flysch rocks trending in a northwestsoutheasterlydirection, which often divert thegeneral southwesterly flow of streams parallelto the Dinaric direction (NW-SE) and stimulatesuperficial drainage, while on the karst rockscanyons are developed. The canyons alongthe rivers Krka, Zrmanja and Cetina (Fig. 19)are up to 180 m deep and were even deeperduring Ice ages, when the sea level was lowerand travertine dams (Fig. 18) were probably27