NEW SOURCE OF WATER FOR SETTLEMENTS ON DUG1 OTOK ISLAND (CROATIA) Rudarsko-geoloSko-naftni zbornik Mladen ZELENIKAI, Boio SOLDOI, Neven TRENC2 IGeotehnifki fakultef Varaidin, Hallera 7, HR-42000 Varaidin, Croatra 25 U "Park prirode Medvednica ", HR-10000 Zagreb, Croat~a Vol. 13 Key-words: Water supply, Safe yield, Pumping test, Water-source The water demand in Southern Croatia, where Dugi Otok is situated, is the highest during the summer due to tourism, irrigation requirements and intensive use of water by local dwellers and those in holiday-homes. The availability and cost of safe water there, varies greatly from one settlement to another. Some rural areas and many Adriatic islands re- mote from regional water-supply systems don't have sufficient safe wa- ter, and dwellers are forced to buy at a high price, water supplied by water carriers (truck-tanks and ship-tanks) during the long summer sea- son. Therefore, a pilot water-supply project has been implemented at Dugi Otok island. The useful experience gained from this project can be applied in many other rural settlements in Southern Croatia and wider, after adequate surveying and analysis. Introduction str. 3946 Previous publications that address the water supply prob- lems at Island Dugi Otok include F r i t z et al. (1977) and Z e 1 e n i k a & F r i t z (1 994). Geotechnical faculty Varadin, Geological Institute Zagreb and MA-Nafiaplin, Zagreb, posses some unpublished professional reports and data related to the investigationof water at Dugi Otok. These data together with results of some additional hydrogeolog- ical reconnaissancewere utiljzed during selection of local- ity for an additional well at Zmansko polje. Due to the shortage of safe water at Dugi Otok during the summer season, the price of water transported by sea- carrier fiom Zadar's regional water supply system is very high. Therefor a 5 meters deep well has been designed in kmansko polje, where three existing wells used to give up to 3 11s ofwater. Becouse of its small depth and the excava- tion of the designed well was entrusted as an easy job to the local contractor, More complicated task for water engineers was the pumping test procedure to estimate the safeyield. This value is essential for management of water source and its proper use. The safe yield can be laborious to acquire, because many factors may interplay during pumping test, including capacity of the pump, present condition of the well, the properties of aquifer, decline of groundwater level due to the interference of longer drought period and pumping in other wells, interference of the tide (sea), floodtide etc. Publications by G r o u t et al. (1992), C 1 ark e and R u s h t o n (1990) and S k i n n e r (1988), relate to wells in the Chalk aquifer of the United Kingdom. The Chalk aquifer has many similaritieswith the aquifers in karstified !mestone at Dugi Otok. These papers explain many of the important issues in safe yield assessment, except the meth- odology. The formal methodology is described by B e e - s 0 n at al. (1997). This paper presents the results of construction and test- ing of a new source of water. This new source is expected to provide additional safe water at a smaller distance fiom Zagreb, 200 1. KljuCne rijeri: Vodoopskrba, Sigurna kolitina crphenja, Probno crpljenje, IzvoriSte vode Potreba za vodom u j u h o j Hrvatskoj gdje se nalazi Dugi otok, naj- veCa je tijekom ljeta zbog turima, navodnjavanja, te intenzivnog korig- tenja vode od strane domaCeg stanovniStva I onog u kuCama za odmor Cijena pitke vode znatno varira od jednog naselja do drugog. Neka ru- ralna podrutja i mnogi Jadranski otoci, udaljeni od regionalnih vodoop- skrbnih sustava, nemaju dovoljno pitke vode i tamoSnji stanovnici su prisiljeni tijekom duge ljetne sezone kupovati po visokoj cijeni vodu koju dopremaju kamioni-cisteme. Stoga je probni vodoopskrbni projekt realizirk na Dugom Otoku. Iskustva dobivena na ovom projektu mogu se nakon odgovarajukeg terenskog snimanja i analiza korisno primije- niti u mnogim ruralnim naseljima u j u h o j Hrvatskoj i Sire the biggest settlements at Dugi Otok. The selection of the deepest advisable pumping water level (DAPWL), plot- ting od drought-bounding c we and data requirements for the assessment of safe yield will be discussed in the paper. The diary of a local engineer 2. M o r o v i C (1994-1996) was a very usehl source of operational data related to wells at Malo Jezero (Fig. 2). Therefor Mr. MoroviC was an im- portant crewmember during the implementation of purnp- ing test in October of 1999 and all other operations there. General data Dugi Otok (Long Island) is the longest and the biggest Island in the Zadar Archipelago. It is a boundary island with very steep cliffs facing open sea, but on its eastern side, there are 1261 ha of arable land with 99000 olive trees and 215000 wine-stocks. For that reason, human set- tlements have developed along the eastern side of the is- land. The area of Island is 114 km;! with approximately I600 permanent dwellers in 550 households. Almost 1200 dwellers are concentrated around the Zmansko polje and many hydrogeologists have tried to prove enough ground- water to meet their water demand. The principle problems on the island are water supply and traffic links. The average precipitation in Zadar for the period fiom 1961 to 1979 was 974 mm. The seasonal variations are considerable, i.e. during 3 summer months precipitation amounts to 204 mm, autumn 360 mm, winter 224 mm and spring 178 mrn. The precipitation recorded for year 1999 in Sali at Dugi Otok, was 773 mm only. At Dugi Otok there are no rivers. However, the floods of Zmansko polje occur every year during the wet season, and more than a half mil- ljon of cubic meters of water can be accumulated there. Zmansko polje is an orographically isolated catchment area around Veliko and Malo Jezero with a size of 4,10 to 5,8 km2 (F r i t z et al. 1977). Veliko Jezero has altitude of 1,5 m and Malo Jezero 2,O m approximately.The flood on Malo Jezero (higher) occurs every year before the flood on Ve- liko jezero (lower), but flood lasts longer at Veliko Jezero.