Search

Bringing INnovation to onGOing water management – a better future under climate change. This report D3.6 provides an overview of the benefit of the BINGO modelling approach for 14 sites in 6 countries. Even though the sites are diverse, as they each tackle different water problems that are typical for Europe, the combination of bottom-up knowledge and data with top-down modelling strategies (climate change data, scenarios) has been successful. At the some of the sites, e.g. in the Netherlands and Germany, individual models had already been implemented, but have been further developed or joined by additional models within BINGO.

Op 21 september 2018 was de openbare verdediging van het proefschrift "Evaporation from dry dune vegetation" door Bernard Voortman. Het proefschrift biedt kwantitatieve inzichten in het verdampingsgedrag van droogteminnende duinvegetaties in vroege successiestadia (kaal zand, mos, gras en heide). We onderzochten onder andere de invloed van het dichtgroeien van natuurgebieden en van het veranderende klimaat op de verdamping. Deze inzichten komen ten goede aan betere grondwatermodellen, maar ook aan de vergroting van de grondwateraanvulling via een gericht vegetatiebeheer.

Coastal and inland dunes provide various ecosystem services that are related to groundwater, such as drinking water production and biodiversity. To manage groundwater in a sustainable manner, knowledge of actual evapotranspiration (ETa) for the various land covers in dunes is essential. Aiming at improving the parameterization of dune vegetation in hydrometeorological models, this study explores the magnitude of energy and water fluxes in an inland dune ecosystem in the Netherlands. Hydrometeorological measurements were used to parameterize the Penman–Monteith evapotranspiration model for four different surfaces: bare sand, moss, grass and heather. We found that the net longwave radiation (Rnl) was the largest energy flux for most surfaces during daytime. However, modeling this flux by a calibrated FAO-56 Rnl model for each surface and for hourly time steps was unsuccessful. Our Rnl model, with a novel submodel using solar elevation angle and air temperature to describe the diurnal pattern in radiative surface temperature, improved Rnl simulations considerably. Model simulations of evaporation from moss surfaces showed that the modulating effect of mosses on the water balance is species-dependent. We demonstrate that dense moss carpets (Campylopus introflexus) evaporate more (5 %, +14 mm) than bare sand (total of 258 mm in 2013), while more open-structured mosses (Hypnum cupressiforme) evaporate less (-30 %, -76 mm) than bare sand. Additionally, we found that a drought event in the summer of 2013 showed a pronounced delayed signal on lysimeter measurements of ETa for the grass and heather surfaces, respectively. Due to the desiccation of leaves after the drought event, and their feedback on the surface resistance, the potential evapotranspiration in the year 2013 dropped by 9 % (-37 mm) and 10 % (-61 mm) for the grass and heather surfaces, respectively, which subsequently led to lowered ETa of 8 % (-29 mm) and 7 % (-29 mm). These feedbacks are of importance for wate

Samen met de neerslag, en eventuele oppervlakteafvoer, bepaalt de verdamping de hoeveelheid water die doorsijpelt naar het grondwater. Een nauwkeurige bepaling van de verdamping in hydrologische modellen is daarom van belang voor nauwkeurige simulaties van de grondwateraanvulling en de hoogte en dynamiek van de grondwaterstand. Dat geldt voor de heersende weerscondities, maar ook voor scenario-analyses zoals klimaatprojecties. Nagenoeg alle regionale hydrologische modellen gebruiken gewasfactoren voor het vaststellen van de potentiële verdamping. In dit artikel laten we zien dat het gebruik van deze empirische factoren kan resulteren in aanzienlijke fouten in de potentiële verdamping, en daarmee in de grondwateraanvulling. Vooral voor bossen kan de fout in het neerslagoverschot door gebruik van gewasfactoren tientallen procenten bedragen, zelfs als verdamping van interceptiewater expliciet wordt gesimuleerd. De conclusie dat het gebruik van gewasfactoren met grote onzekerheden is omgeven is niet nieuw. Hier laten we echter zien dat ook voor langjarig-(klimaat)-gemiddelde schattingen van de potentiële verdamping, de gewasfactorbenadering moet worden afgeraden. Voor nauwkeurige hydrologische analyses is het nodig te investeren in meetgegevens en op basis daarvan het verdampingsproces in modellen beter te schematiseren. Dit geldt niet alleen voor klimaatprojecties, maar ook voor het huidige klimaat.

Over de gevolgen van droogte voor de soortensamenstelling en de verdamping van grondwateronafhankelijke duinvegetaties is heel weinig bekend. Op basis van verkennend onderzoek verwachten we dat meer droogte in de zomer leidt tot een toename van het aandeel mossen en kale grond. Daardoor daalt de verdamping en neemt de winderosie toe. Klimaatverandering zou zo gunstig kunnen uitpakken voor zowel de noodzakelijke dynamiek in het duin, als voor de aanvulling van de ondergrond met neerslagwater

In deltaic areas with saline seepage, freshwater availability is often limited to shallow rainwater lenses lying on top of saline groundwater. Here we describe the characteristics and spatial variability of such lenses in areas with saline seepage and the mechanisms that control their occurrence and size. Our findings are based on different types of field measurements and detailed numerical groundwater models applied in the south-western delta of the Netherlands. By combining the applied techniques we could extrapolate measurements at point scale (groundwater sampling, temperature and electrical soil conductivity (TEC)-probe measurements, electrical cone penetration tests (ECPT)) to field scale (continuous vertical electrical soundings (CVES), electromagnetic survey with EM31), and even to regional scale using helicopter-borne electromagnetic measurements (HEM). The measurements show a gradual mixing zone between infiltrating fresh rainwater and upward flowing saline groundwater. The mixing zone is best characterized by the depth of the centre of the mixing zone Dmix, where the salinity is half that of seepage water, and the bottom of the mixing zone Bmix, with a salinity equal to that of the seepage water (Cl-conc. 10 to 16 g l-1). Dmix is found at very shallow depth in the confining top layer, on average at 1.7 m below ground level (b.g.l.), while Bmix lies about 2.5 m b.g.l. The model results show that the constantly alternating upward and downward flow at low velocities in the confining layer is the main mechanism of mixing between rainwater and saline seepage and determines the position and extent of the mixing zone (Dmix and Bmix). Recharge, seepage flux, and drainage depth are the controlling factors.

Karst-related flooding occurs in several depressions between Le Roy and Caledonia, NY, USA. The timing of these flood events suggests that a regional groundwater phenomenon contributes to the flood volumes, in addition to contributions by surface water and subsurface quickflow. To gain better understanding of the proportions of these components, two watersheds near Le Roy (Britt Road and Quinlan Road) were studied in detail. A rainfall-runoff model was constructed in the PCRaster language to quantify the portion of flood volume originating from surface runoff for two different flood events. For an event in October 2006, runoff explained the entire flood volume in the Quinlan Road watershed. For an event at the end of November 2006, the contribution of surface runoff to the flood volume was about 49% and 46% for the Britt Road and Quinlan Road watershed, respectively. The remaining part of the flood volume must have been derived from subsurface quick flow or groundwater. In these model simulations swampy areas and the flood zone were assumed to be impermeable, simulating the presence of a high water table. Without this assumption all the surface water entering the flood zone would infiltrate into the subsurface. From a sensitivity analysis it was found that microtopography storage is an influential parameter in runoff generation in these watersheds. These findings suggest that high groundwater levels are the main driving force behind the floodings. Without a groundwater level close to the land surface in the Britt Road watershed or groundwater mounding at the sinkholes in the Quinlan Road watershed, no flooding would occur. However, to accurately quantify the quickflow and groundwater components contributing to the floodings, additional research needs to be performed at the actual time of flooding.