Session K.pdf - Clarkson University

Differance [ o C]5.004.003.002.001.000.00-1.00-2.00-3.00-4.00FR1 - unregFR2 - unregDR - unreg1. jan.1. feb.1. mar.1. apr.1. mai.1. jun.1. jul.1. aug.1. sep.1. okt.1. nov.1. des.Differance [ o C]5.004.003.002.001.000.00-1.00FR1 - unregFR2 - unregDR - unreg-2.00-3.00-4.001. jan.1. feb.1. mar.1. apr.1. mai.1. jun.1. jul.1. aug.1. sep.1. okt.1. nov.1. des.Fig. 7. Water temperatur differences between simulated values at a regulation regime and at anunregulated river. The differences have been smoothed with a sliding 30 day average. The upper figureshows the differences just downstream lake Suldalsvatn (Suldalsosen) and the lower figure shows thedifferences at the outlet to the sea (Tjelmane)CONCLUSION• Low discharge in the river increases the energy exchange with the atmosphere.• Ice production will be more frequent with low winter discharge (FR2 and DR) in thelower part of the river. In our five year test period the number of days with ice productionwere five-doubled from the observed 9 to 41 when we lowered the discharge from12 m 3 /s to 6 m 3 /s, but even then the ice periods seldom lasted more than 20 days.• Low discharge in spring and early summer (FR2) yields higher water temperaturein the river. The temperature in the lower part of the river will be 3-4 o C higher thanboth the unregulated river and a river with the other suggested regulation regimes. Inthe upper part the river will be 1-2 o C warmer than in the unregulated case, and 2-3 o Cwarmer than in the other regimes. Day to day and year to year variations increaseswith low discharge.• In dry summers in August-September a downscaled natural discharge (DR) willgive 1-2 o C warmer water than the in other regimes, and almost as warm as in the unregulatedriver.365