The geology, hydrology, and hydrogeology of Haiq-Ardibo catclilllent was studied. The mainrnobjectives is to understand and map the different lithologic units and characterize them in tornhydrostratigraphic units, to analyze the water balance of the catchment including lakes Haiqrnand Ardibo. Hydrochemical and bathymetric studies were also conducted.rnThe geology of the area was mapped at the scale of 1: 50, 000 and this was used as a basis tornestablish the hydrogeological map by taking into account the permeability, geomorphicrnsetting and recharge conditions.rnTwo major hydrostratigraphic units are mapped. These are the Quaternary unconsolidatedrnsediments and the fractured volcanic rocks, both having a good permeabitlity. Due tornmorphologic setting, the fractured volcanics are refen'ed to as poor aquifers, but goodrnrecharge zones, recharging the QuaternalY unconsolidated sediments that occupy low lyingrnflat areas in the studied catchment.rnLand use/land cover, soil, and slope maps of the area were prepared so that the rate ofrnevapotranspiration for a vegetation-soil complex is computed, and the runoff into lake Haiqrnand Ardibo estimated.rnAreal mean arumal rainfall was analyzed using arithmetic mean of the long telID mean alillualrnrainfall of four stations, Thiessen weighted averages of these stations and Isohyetalmethods;rna value of 1158.5 mm depth was obtained by taking the average of the first two methods.rnOpen water evaporation on the lakes surface was estimated using Pan evaporation data,rnradiation, Penman , and mass transfer approaches. The first three methods gave reasonablernvalues and the average was taken and is 146.5 mm depth over the surface of the lakes.rnPotential evapotranspiration (PET) computed using modified Perunan gave 1200 nun depthrnover the area of the studied catchment.. Using the computed PET and effective rainfall,rnactual evapotranspiration and groundwater recharge over the catclunent using Thornthwaiternand Mather (1957) soil-water balance method obtained is 805 and 43.2 mill respectively Runoff into the lakes was also calculated using a weighted average mnoff coefficient of thernHaiq and Ardibo subcatchments taking in account soil, slope, and vegetation cover. Anrnannual nmoff into lake Haiq and Ardibo is 18.82 and 12.68 million cubic meter (mcm)rnrespectively.rnTaking into consideration all the inflows and outflows into the catchment and lakes, thernwater balance of the studied area was analyzed. The annual inflow into lake Ardibo isrnestimated to be 30.98 mcm and outflow is 26.3 mcm. The residual found is 4.68 mcm.rnRepresenting the groundwater net flux. Using a Darcy, the groundwater outflow from lakernArdibo is estimated to be 3.2 mcm. The groundwater inflow into this lake therefore is 1.48rnmcm. In the same way the atmual input into lake Haiq is 46.83 mcm. and the outflow is 33.4rnmcm, the residual remaining in the balance is 13.43 representing the net groundwater flux.rnThe water balance computed for the entire study area is estimated to be 162.3 mcm. inflowrnand 138.434 mcm out flow. The residual found is therefore 23.87 mcm, assuming that therngroundwater divide coincides with the surface water divide, the residual tenn is the annualrngroundwater outflow from the studied catchment.rnThe current bathymetric survey indicates that both lakes have experienced significant lakernlevel reduction. This lake level change is attributed to land use changes, neotectonics andrngeneral decrease in the rainfall of the area.rnHydrochemical study of the surface and groundwater indicated two major water types. Thernsurface water being magnesium bicarbonate type, while the groundwater is calciumrnbicarbonate type . Further observation of the cheInistry of the ground and surface waterrnbodies indicated that the waters are suitable for irrigation. Except for the trace non metals,rnthe chemical analysis of the inorganic constituents show that the water is potable provided,rnbacteriological analysis should be done