Session K.pdf - Clarkson University

constant inclination. The channel shape and the bottom roughness was optimized to fitthe measurements.UNREGULATED FLOWThe water temperatures with an unregulated flow were calculated for the period 1931-2002. The first regulation upstream lake Suldalsvatn started in 1966, but the majorchange in Suldalslagen came after the start-up of Kvilldal and Hylen power stations in1980. Today most of the water from Lake Suldalsvatn leaves through Hylen directly tothe sea.The most complete weather data available were from Bergen 100 km to the northwest.The air temperature were adjusted to fit the Suldal area, and the wind strength were indirectlytuned in the model by the setting of a wind coefficient (=0.85). We had sufficientof discharge measurements to construct an unregulated discharge series with a correlationcoefficient above 0.9. The really weak point in the input data was the completelack of water temperature measurements in the major rivers. Upstream lake Suldalsvatnthere are some lakes that affects the water temperature. After some test runs we concludedthat the temperature into the lake was similar to the temperature at Tjelmanewhere Suldalslågen enters the sea, both temperatures affected by lakes. We reconstructeda water temperature series based on this knowledge and correlation betweenmeasured air temperatures (Bergen) and water temperatures.We ran the QUAL2E model from 1931 to 2002 and obtained a water temperature seriesfor unregulated condition at the outlet of lake Suldalsvatn (Suldalsosen). From measurements(see Fig. 3) we calculated the standard deviation in the error to be 0.7 o C on amonthly basis and 0.8 o C on a daily basis. Compared with the natural variations this isquite satisfactory considering the relative poor input data. The largest errors occur inJanuary-February when the model often got a lower water temperature than what wasobserved. This was probably caused by an ice cover on the lake which forms in somecold and calm periods. The model did not manage to build an ice cover, probably due todaily averaged wind data that seldom gave zero wind.Water temperature [ o C]18.0016.0014.0012.0010.008.006.004.002.000.00T observedT simulated1967 1968 1969 1970 1971 1972 1973Fig. 3. Observed and simulated water temperatures at Suldalsosen from 1967-73We also modelled the unregulated water temperature at the lower end of Suldalslågenusing RICE. We used the output from the QUAL2E model as upstream input in theRICE model. Fig. 4 shows an example of the simulated and observed values.361