The Surface Water Department of the Czech Hydrometeorological Institute in 2006 selected a new period for the evaluation of hydrological characteristics of mean daily discharge series. Initially, two fortyyear long periods were considered: 1961-2000 and 1966-2005 and the period of 1961-2005 was finally accepted. Comparison of the still used 1931-1980 period with the new one was carried out using the data from 50 Czech gauging stations that had continuous data time series. The mean long-term runoff of Czech rivers changed very little from 1931-1980 to 1961-2005. Comparison of the variation coefficients brought similar results. However, among specific M-day discharges the low flow values (e.g. Q355d) showed a significant increase. This might reflect not only natural causes but could suggest anthropogenic factors as well. Trend analyses started with testing mean annual runoff at 65 Czech gauging stations that were not influenced by human activity. 34 stations showed an increasing trend and 31 a decreasing trend. However, the trend was statistically significant only at one station. Trends of individual months dramatically differentiate. In January through March the increasing trends prevail. March trends show the highest number of stations with a significant increase. The three following months are complete opposites in which decreasing trends dominate. In May and June, not a single increase was recorded and many decreases were statistically significant. Almost no significant trends were examined in the months of the second half of the year. and V posledních měsících se oddělení povrchových vod ČHMÚ zabývalo výběrem období pro výpočet nových hydrologických charakteristik M-denních průtoků na českých tocích. Uvažována byla čtyřicetiletí 1961-2000 a 1966-2005, nakonec však bylo přijato období 1961-2005. Na datech z 50 vodoměrných stanic, které měly nepřerušené řady pozorování, bylo uskutečněno první srovnání statistických charakteristik období 1931-1980 (doposud používané) a 1961-2005. U nového období byly u neovlivněných stanic vyhodnoceny trendy průměrných ročních průtoků a průtoků jednotlivých měsíců.
Forecasting the river flow level and volumes are essential to making the most efficient use of rivers and in minimizing damages to flood. A relationship between the released discharges from Mosul dam and river levels in Mosul station is predicted with high correlation coefficient for the two periods within the year (rainy and non-rainy months). A time series technique analysis for predicting the best relevant statistical model for future forecasting of Tigris River levels within the river reach between Mosul dam and Mosul city was applied. Deterministic prediction of the water levels of Tigris River within the reach between Mosul dam and Mosul city will help to avoid the increasing of the water level within the river reach to minimize the damages which may occur due to inundation areas. The average monthly Tigris River stages of Mosul station for the two periods before and after Mosul dam construction are constant with a reduction in the average value of the maximum water stages and increasing the average value of the minimum water stages after Mosul dam construction. Through the statistical analysis of the time series of the available river stages data at Mosul station, a repetition in the annual cycle in the water stages before Mosul dam construction and a decreasing trend through this period was observed. Winter model is the most suitable time series model to forecast the Tigris River stages or any missing data in the future in the Tigris River reach between Mosul dam and Mosul city. and Predpoveď vodných stavov a prietokov vodných tokov je podstatná pre ich efektívne využitie a minimalizáciu povodňových škôd. Závislosť medzi výtokom z priehrady Mosul a stavom vody v rieke v stanici v Mosule bola určená s vysokou hodnotou súčiniteľa korelácie pre dve obdobia roka (zrážkové a bezzrážkové obdobie). Na analýzu časových radov sme použili najvhodnejší štatistický model, ktorý umožnil predpoveď vodných stavov Tigrisu medzi priehradou Mosul a mestom Mosul. Deterministická predpoveď vodných stavov Tigrisu môže pomôcť minimalizovať škody v záplavovom území. Priemerné mesačné stavy vody v hydrologickej stanici v Mosule na rieke Tigris pre dve obdobia - pred vybudovaním priehrady Mosul a po ňom - sa nemenia, ale priemerné hodnoty maximálnych stavov vody po vybudovaní priehrady v Mosule sa znížili, naopak minimálne hodnoty vodných stavov sa zvyšujú. Štatistickou analýzou časových radov dostupných vodných stavov v stanici Mosul sa zistila nemennosť vodných stavov počas ich ročného cyklu pred vybudovaním priehrady Mosul a po jej vybudovaní. Najvhodnejším modelom časových radov pre predpoveď vodných stavov v rieke Tigris, alebo pre predpoveď chýbajúcich hodnôt vodných stavov v úseku rieky medzi priehradou a mestom Mosul, sa ukázal zimný model.