The influence of the crest height of trajectory 225 on the water level at Kampen

Abstract

The water levels along the dike of Kampen are affected by the magnitude of the discharge on the IJssel and the water level set-up caused by the wind characteristics on the IJsselmeer. The Kampereiland has been assigned as a retention area to reduce the water levels near Kampen during a storm. This area should store excess water during a storm at the IJsselmeer of a magnitude corresponding to an annual exceedance probability of 1/500, to prevent this water from flowing in the direction of Kampen. The Kampereiland is protected by dike trajectory 225 and a part of this trajectory has been made resistant to the overflow of water. According to new insights, the crest of this dike section seems too high and the Kampereiland inundates less frequently. Furthermore, not sure is whether the water level at Kampen benefits from the inundation of the Kampereiland and what the consequences are for surrounding dikes. The Kamperzeedijk is one of these surrounding dikes and protects the city IJsselmuiden, along with the polder behind. The influence of the crest height of this overflow resistant part on the water levels at Kampen and at IJsselmuiden is investigated. The most important assumptions are that dikes do not breach and that the water level at Kampen remains constant after water flows into the Kampereiland. The influence on the water levels at Kampen and at the Kamperzeedijk is evaluated for multiple crest heights of the overflow resistant dike section. Eventually, these water levels are processed with a statistical model to compute multiple water level exceedance frequency lines for each location and for various chosen crest heights of trajectory 225. The results show that higher crest heights of trajectory 225 lead to increased maximum water levels at the Kamperzeedijk and to lower maximum water levels at Kampen, and vice versa. The water levels in front of the overflow resistant dike section remain unaffected. The return periods for overflow at Kampen and IJsselmuiden are derived by comparing the water level exceedance frequency lines to their individual crest heights. Concluded is that the inundation of the Kampereiland does not immediately lead to a load increase in front of the Kamperzeedijk. A delay is observed as a result of the storage capacity of the Kampereiland. As soon as water from the Kampereiland flows into the Ganzendiep, the loads rapidly increase. Furthermore, concluded is that the Kampereiland is capable of reducing the water levels at Kampen. Based on the results from this research, a crest height of 2.7m +NAP leads to equal return periods for overflow at trajectories 10-2 and 11-2. The reduction of the crest height by ten centimeters increases the return period for overflow at Kampen from 30,000 years to 45,000 years. At the Kamperzeedijk, the return period is reduced from 80,000 years to 45,000 years. In reality, these return periods are also affected by other failure mechanisms. A full dike assessment has to elaborate on this. Furthermore, trajectory 225 is assessed whether it meets its safety standard. It would be more legitimate to assess trajectory 225 by explicitly quantifying its consequences on trajectories 10-2 and 11-2