HKV (Netherlands)

Abstract Understanding the hydraulic connection between groundwater sources and coastal wetlands, as an ecosystem dependent on groundwater, plays a crucial role in the protection and management of coastal wetland ecosystems. This study focuses on the hydraulic management of the Anzali coastal wetland, situated in a shallow coastal aquifer with numerous rivers flowing into it. To investigate the intricate hydraulic interplay between surface water and groundwater, the MIKE SHE model was employed. The results revealed that the groundwater level surrounding the wetland is lower than the water level within it. Consequently, the study evaluated options for controlling groundwater extraction (scenarios 1 and 2) and river management (scenarios 3 and 4) in three different conditions: drought, extreme drought, and normal years. The study focused exclusively on how different scenarios affect the groundwater level of the wetland area, despite the known significant impact of changes in river flow on wetland water protection. The findings demonstrated that changes in groundwater extraction significantly affect the groundwater level, particularly in drought conditions. The results show that changes in groundwater extraction have a significant impact on the groundwater level, especially in drought conditions, such that in these conditions, the first and second scenarios result in an average decrease of 0.96 meters and an increase of 1.56 meters in the groundwater level in some areas close to the wetland. The results of the scenarios 3 and 4 caused minimal changes in the groundwater level, with the most significant impact observed in observation well located near the river.

Abstract. Managing the water and flood risk in low-lying polder regions depends on the performance of canal dikes. This performance is influenced by hydraulic heads, which can peak due to heavy rainfall, affecting their stability and potentially inducing dike breaches. Variations in head responses and head statistics are relevant for regional flood risk analysis of canal dike systems. This study examined the dynamics of peak heads in canal dikes on a national scale using time series models calibrated on a unique dataset of head observations across the dike system. Various model structures were evaluated, and a non-linear model performed the best. These models were used to simulate 30 years of head time series representing current and future climate scenarios. Subsequently, dike clusters were identified based on the coincidence of peak heads, allowing for the identification of dikes where peaks are caused by (dis)similar types of rainfall events. The differences and similarities in peak head response between dikes and identified clusters were related to physical dike characteristics. While the subsurface material and dike width appeared to influence the head response variation of clusters, their presence across multiple clusters indicates that they do not yield a definitive outcome. Moreover, peak head statistics across various dikes indicated that extreme and yearly occurring load conditions are relatively close to each other, with a median decimate height of only 15 cm. With climate change driving higher winter precipitation and summer evaporation, head statistics are changing. By 2100, extreme peak heads are expected to occur between 3 times less and 8 times more frequently, depending on the climate scenario and the type of canal dike.

<strong class="journal-contentHeaderColor">Abstract.</strong> Uncertainties in the rate of sea level rise, coupled with ongoing urban expansion, create challenges for city planners in designing flood risk adaptation strategies. This study analyzes flood exposure rates in Rotterdam's unembanked areas from 1970 to 2150. We modeled flood hazards for 10&ndash;1000 year return periods under both low (RCP2.6) and high (RCP8.5) emission scenarios, while assessing exposure using historic and planned urban development data. Without adaptation measures, flood exposure in Rotterdam&rsquo;s unembanked areas is projected to increase. For 10-year flood events under RCP8.5, exposure rates are expected to increase 7-fold by 2150 compared to 2020. For RCP2.6, a 3-fold increase is projected, reflecting uncertainties in long-term sea level rise. A retrospective analysis reveals an improvement in flood exposure: exposure levels observed in 2020 were approximately half those observed in 1996, due to construction of the Maeslant storm surge barrier. Temporal variations in exposure rates are attributed to three factors: urban development, sea level rise, and the construction of the Maeslant barrier. Exposure rates are primarily influenced by the Maeslant barrier, followed by sea level rise and urban development. Understanding the interplay of these three factors is crucial for urban planning and flood risk management in delta cities.

Backward erosion piping (BEP) is a failure mechanism of hydraulic structures like dams and levees on cohesionless foundations subjected to seepage flows. This article models the time-dependent development of BEP using numerical simulation of the erosion process. A 3-dimensional finite element equilibrium BEP model is extended with a formulation for the sediment transport rate. The model is compared to and calibrated with small- and large-scale experiments. Finally, a large set of simulations is analyzed to study the effects of factors such as grain size, scale (seepage length) and overloading on the rate of pipe progression. The results show that the development of BEP in the small-scale experiments is predicted well. Challenges remain for the prediction at larger scales, as calibration and validation is hard due to limited large-scale experiments with sufficiently accurate measurements. The results show that the progression rate increases with grain size and degree of overloading and decreases with seepage length, which is consistent with experimental observations. The model results provide a better physical basis for incorporating time-dependent development in the risk assessment and design of levees.

Abstract Flood events are expected to increase in their frequency and severity, which results in higher flood risk without additional adaptation measures. The information gained from flood risk models is essential in effective disaster risk management. However, vulnerability estimations are often a large driver of uncertainty, and flood damage is rarely estimated due to a lack of empirical damage data from flood events. This study uses a unique data set with experienced damages and the implementation of flood damage mitigation (FDM) measures on the household level, collected after the flood event in the Netherlands in 2021. Flood damage models that control for several hazard, exposure, and vulnerability indicators are estimated and allow for additional input in flood risk models. Previous estimates of the effectiveness of FDM measures are prone to a selection bias, as households that do, and do not implement FDM measures systematically differ in their risk profiles. By using an instrumental variable‐estimation, this study overcomes this selection bias and finds significant reductions in flood damage due to FDM measures. These reductions can be incorporated in multivariate flood vulnerability estimations, which indicate that FDM measures significantly reduce flood damage. Providing information on flood hazard, as well as implementing early warning systems, is crucial for ensuring effective flood risk management.

Natural disasters, such as flood events, are expected to increase in their frequency and severity, which results in higher flood risk without additional adaptation measures. The information gained from flood risk models is essential in flood risk management. However, vulnerability model components in the form of depth-damage curves are often a large driver of uncertainty and empirical vulnerability curves are rarely estimated due to a lack of damage data from flood events. This study uses a unique dataset with experienced damages and the implementation of flood damage mitigation (FDM) measures on the household level, collected after the flood event in the Netherlands in 2021. Two main findings emerge from an analysis of this dataset. First, depth-damage curves that control for several hazard, exposure and vulnerability indicators are estimated. These curves serve as an update to current input in flood risk models, where previous vulnerability estimates from the Netherlands are based from a flood event in the 1950s. Second, it is found that previous studies on the effectiveness of FDM measures are prone to a selection bias, as households that do and do not take FDM measures systematically differ in their risk profiles. By using an Instrumental Variable (IV)-estimation, this study overcomes this selection bias and finds significant reductions in flood damage to both buildings and household contents due to FDM measures.

For efficient management of the Dutch surface water reservoir Lake IJssel, (sub)seasonal forecasts of the water volumes going in and out of the reservoir are potentially of great interest. Here, streamflow forecasts were analyzed for the river Rhine at Lobith, which is partly routed through the river IJssel, the main influx into the reservoir. We analyzed multiple seasonal forecast data sets derived from EFAS, E-HYPE and HTESSEL, which differ in their underlying hydrological formulation, but are all forced with similar input from the ECMWF SEAS5 meteorological forecasts. We post-processed the streamflow forecasts using quantile matching (QM) and analyzed several forecast quality metrics. Forecast performance was assessed based on the available reforecast period, as well as on individual summer seasons. QM increased forecast skill for nearly all metrics evaluated. Particularly HTESSEL, a land surface scheme that is not optimized for hydrology, needed the largest correction. Averaged over the reforecast period, forecasts were skillful for the longest lead times in spring and early summer. For this period, E-HYPE showed the highest skill; Later in summer, however, skill deteriorated after 1–2 months. When investigating specific years with either low or high flow conditions, forecast skill increased with the extremity of the event. Although raw forecasts for both E-HYPE and EFAS were more skilful than HTESSEL, bias correction based on QM can significantly reduce the difference. In operational mode, the three forecast systems show comparable skill. In general, dry conditions can be forecasted with high success rates up to three months ahead, which is very promising for successful use of Rhine streamflow forecasts in downstream reservoir management.

The river bed level in low-land rivers like the Rhine branches in The Netherlands changes continuously on various spatial and temporal scales. Large-scale degradation occurs in many rivers due to river-wide engineering interventions, such as channelization, in the last decades and centuries. Local river interventions, such as the construction of side channels, affect the river's morphology by mainly causing sedimentation over the length of the intervention. This sedimentation occurs at a smaller spatial scale than the erosion due to channelization. On an even smaller spatial scale, dune-like bedforms migrate along the river bed but these have a net-zero effect on the morphology. This shows that bed-level changes occur on different spatial scales. Disentangling these spatial scales is appealing from a river management point of view since mitigating large-scale degradation requires a different river management strategy than mitigating erosion and sedimentation due to local interventions.We use detailed bed-level measurements to study the morphological changes on multiple scales using a wavelet transform. A wavelet transform is, unlike a Fourier transform, able to distinguish and disentangle the bed-level changes on different spatial scales while taking into account its spatial variation. Using the wavelet transform, we can disentangle the bed level change caused by a local intervention from the large-scale bed degradation. Both bed level changes are in the same order of magnitude and thereby difficult to determine without filtering. This allows us to study the morphological changes resulting from a single river intervention. The results show that interventions such as side channels cause an average bed-level increase around which the bed level fluctuates. This dynamic component can be up to 6 times larger than the average change. The average bed level increase is in the same order of magnitude as analytical estimations for the equilibrium bed level change.Disentangling spatial scales of bed level changes gives a better understanding of the impact of local interventions and past channelization. These insights can be used to optimize the operation and management of the river and thereby accommodate the main river functions.

&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;Based on the notion that Flood risk communication contributes to Disaster Risk Reduction (DRR), a novel community-centred approach called &amp;amp;#8220;Our Flood Mural&amp;amp;#8221;/&amp;amp;#8220;Nosso Mural de Cheias&amp;amp;#8221; was tested in Beira, Mozambique. &amp;amp;#8220;Our Flood Mural&amp;amp;#8221; centres around the co-creation of an interactive mural painting that highlights local experiences of past flood events, informs on the existing flood risk in the area and suggests possible risk-reducing measures. The mural brings together local knowledge and arts, and modern information technologies. &amp;amp;#8220;Our Flood Mural&amp;amp;#8221; can easily be upscaled and adapted to the local context in various settings. &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;A key part of &amp;amp;#8220;Our Flood Mural&amp;amp;#8221; was active engagement with the local community. Survey results and plenary community sessions were held and showed that the people of the targeted community have a broad understanding of what they can do to reduce flood risk, such as strengthening of rooftops, moving to higher ground, and freeing drainage canals from clutter. These shared experiences were incorporated in the design of the mural which was made by a local artist. Also, two interactive QR-codes were included on the mural to offer additional (online) information: one linking to local weather forecasts and giving background information on the development process of the mural. The location of the mural was mutually decided to be at a local market where it is exposed to a wide audience on a daily basis. &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;During the implementation of the mural, festivities were organized with local leaders present to draw attention to the purpose of the mural. Local leaders, community members, and aid organisations expressed ownership and pride as well as the desire to expand the idea to other locations and to address societal issues other than flood risk. It was also noticeable that the linkage of the mural to online information drew attention in the community, showing the mural&amp;amp;#8217;s potential as a means of introducing new technologies and information channels to reach a target audience. &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;span&amp;gt;Lessons-learned from our community-centred approach include the importance of organizing plenary sessions and carrying out local surveys to assure accurate representation of the communities&amp;amp;#8217; flood risk situation, and to assure adequate use of imagery and/or text. The visibility and accessibility of the different steps in the co-creation approach can help communities, technical experts, aid organizations, and officials interact constructively and identify potential improvements in each other&amp;amp;#8217;s actions. &amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt;

The aquatic worm Lumbriculus variegatus (Lv) contains high levels of proteins and can provide an excellent fish food. Large-scale production of Lv on low value organic substrates, such as by-products produced during wheat processing, therefore can be a promising and sustainable concept for the aquaculture industry. Growth and reproduction of Lv on different combinations of wheat based derivatives was studied at fixed isoenergetic levels (expressed by the chemical oxygen demand of the food), but at different carbon to nitrogen (C:N) mass ratios under controlled conditions in specifically designed test-beaker tests. Growth and reproduction rates were compared to those on Tetramin®, a substrate known to give excellent growth of Lv. Although Lv did exhibit a growth response on single as well as on mixed wheat fractions, growth was mainly controlled by the C:N ratio of the diets. Lower C:N ratios of typically 6-7 gave a much better performance than high C:N ratios of approximately 20. It was discussed this is probably caused by Lv relying on the presence of proteins for their carbon and energy source. Although growth and reproduction rates were not as high as on the control diet, the results are promising for the development of a worm biomass production system operating on by-products from the wheat processing industry.