Normally the ratio of the discharge between the Nederrijn and the IJssel is given to QWAST, and it is always kept. In this option we allow flexible water distribution between these two Rhine branches. QWAST first tries to meet all the goals, including reaching the correct level of the lakes. If that is reached, then he tries to distribute the water accoriding to the given ratios. Note that by default there is no minimum discharge set by the Nederrijn. The user can set (if necessary) a minimum discharge using the modifier "Aanvoer capaciteiten".

The flexible distribution can be activated in the global properties, setting VERDELING_FLEX=Flex. For usual calculation: VERDELING_FLEX=. In case of flexibe distribution the following rule is used: if the discharge of Lobith is less than 1700 m3/s, the minimum discharge of the Nederrijn is equal to the discharge according to the fix distribution, the maximum is free. Above 1700 m3/s, the minimum discharge of hte Nederrijn 30 m3/s. If the discharge is more/less, it is coming 2/3 from the Waal and 1/3 from the IJssel.

QWAST versie HalfFlex (select VERDELING_FLEX=HalfFlex): the discharge of the Nederrijn is only flexibel above 1700, and only in the sense that it can be less than the fix distribution but not more.

The different options are also shown in the figure below. With blue color, the original distribution of the discharge, this data is provide to QWAST. We compare three calculations:

1) no flex version (organge): the points correspond to the dicharge distribution provided to QWAST (Blue color on the lower figure)

2) flex version with no minimum discharge on the "Nederrijn" (yellow): the results do not correspond all the time to the discharge distribution provided to QWAST. At those points the water was needed to keep the water level of the "IJsselmeer" high enough. It can occur that the "Nederrijn" has almost zero discharge. (Red color of the lower figure)

3) Flex version with minimum discharge on the "Nederrijn" (gray): similar to the above results, but the discharge of the "Nederrijn" was set to be at least 10m3/s. It can be seen that indeed, it never goes below 10m3/s. In this scenario the level of the IJsselmeer is less close to the desired level than in option 2. (Green color of the lower figure)

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