TIME SERIES ANALYSIS OF HYDROLOGIC DATA FOR WATER ...

D. Machiwal, M. K. Jhapredictions from both approaches were compared toidentify the most suitable approach for reliablesimulation. The MK Test suggested no linear trendin monthly maximum data sequences of each mentionedgauge station. Though the error estimatesindicated that the ARIMA model is slightly betterthan the Thomas-Fiering model, both the approachesare recommended for simulating the dailymaximum streamflow of Cekerek Stream.6.2 Surface water qualityHarned and Davenport (1990) analyzed trends inthe water quality data of 1945 – 1988 from majorstreams flowing into the Albemarle-Pamlico estuarinesystem. The nonparametric Seasonal KendallTest indicated a change in the water quality dataduring the 1945 to 1988 period. The evaluation ofwater-quality data and more than 50 basin variablesindicated 121 significant correlations between 11basin characteristics and 12 water-quality constituentsat 21 estuary locations and 7 National StreamQuality Accounting Network stations.Yu et al. (1993) analyzed the surface water qualitydata of the Arkansas, Verdigris, Neosho, andWalnut River Basins, Kansas to examine trends in17 major constituents by using four different nonparametricmethods. The results indicated that theconcentrations of specific conductance, total dissolvedsolids, calcium, hardness, sodium, potassium,alkalinity, sulfate, chloride, total phosphorus,ammonia plus organic nitrogen, and suspendedsediment generally have downward trends. Some ofthe downward trends were related to the increase indischarge, while the others were attributed to thedecrease in pollution sources. The homogeneitytests suggested that both the station-wide trends andbasin-wide trends are non-homogeneous.Robson and Neal (1996) examined the trend often years upland stream and bulk deposition waterquality data from Plynlimon, mid-Wales by applyingthe Seasonal Kendall Test. The plotted data ontime scale showed long-term cycles, which relate tothe fluctuations in weather patterns at Plynlimonand thus violate the assumptions of common statisticaltrend tests. Even though the Seasonal KendallTest was significant for some determinands, thegraphs suggested that many of these trends areunlikely to continue. There was no indication ofchanging acid deposition inputs or changing aciditywithin the runoff, despite a decline in the UK sulphurdioxide emissions. The stream water dissolvedorganic carbon showed an increase over time, butthere was not corresponding decrease in pH asmight be expected from the acidification theory.There were cyclic variations in bulk precipitationand in stream water quality, which indicated thattrends cannot be established even with 10 years ofdata. Therefore, it was strongly recommended thatlong-term monitoring program should continue forseveral decades. It was also emphasized thatgraphical analysis greatly enhances data interpretation,and should be considered as an essential componentfor trend investigation.Kalayci and Kahya (1998) detected linear trendsin the surface water quality of rivers in the SusurlukBasin by employing four nonparametric trend testsviz., the Sen's T Test, Spearman's Rho Test, Mann-Kendall Test and the Seasonal Kendall Test. Thelinear slopes (change per unit time) of trends werecalculated by using a nonparametric estimator. Inaddition, the homogeneity in monthly trends wastested by the Van Belle and Hughes method. Theresults of the nonparametric tests indicated that thedischarge and sediment concentration have downwardtrends, while the temperature, EC and theconcentrations of sodium, potassium, calcium +magnesium, bicarbonate and chloride have upwardtrends. In contrast, the concentrations of carbonate,pH, sulfate, organic matter, and boron have notrends.Harned and McMohan (1997) examined themonotonically increasing or decreasing temporaltrends in riverine water quality including the suspendedsediment, solids, and nutrients for six stationsof the Contentnea Creek Basin by using SeasonalKendall Test. The variation in water qualitybecause of the variation in streamflow was alsoaccounted for in cases where streamflow data wereavailable. The results indicated that the nutrientconcentrations for Contentnea Creek at Hookertonhave declined since 1980. Total nitrogen, nitrate+nitrite,and nitrate concentrations have a significantdeclined trend, with the greatest reductionsoccurring from 1980 to 1992. Total ammonia andorganic nitrogen concentrations, which were increasingduring the 1980's, have declined sincearound 1990. Furthermore, the total phosphorus,dissolved phosphorus and orthophosphorus, whichincreased during the 1980, have shown a significantdecline since 1988 – the first year of the legislatedphosphate detergent ban.Antonopoulos et al. (2001) analyzed the time seriesof water quality parameters and the dischargeof Strymon River in Greece for the 1980 – 1997period. The nonparametric Spearman’s criterion250