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Fosfaatroutes van boerenperceel naar sloot
Deltares en Waterschap Rijn en IJssel hebben op een veehouderij in de Achterhoek detailmetingen gedaan die inzicht geven in de bronnen en routes voor zowel stikstof als fosfaat, met als doel om op basis daarvan de meest effectieve maatregelen te identificeren voor het verminderen van de nutriëntenverliezen naar grond- en oppervlaktewater.
On the bound wave phase lag
More than three decades ago, it was noted that the ocean infragravity bound wave increasingly lags behind the forcing short-wave groups when propagating towards the shore. To date, the most recent theoretical prediction of this so-called phase lag remained a first-order approximation in terms of depth variations. Here, a new semi-analytical solution is proposed which does not rely on this approximation. Strong agreement is obtained when the new solution is compared with high-resolution laboratory data involving both bichromatic and random wave conditions. This newly proposed theoretical phase lag is then extensively compared with the former one, highlighting an increasing discrepancy between the two solutions as the relative bottom slope increases. The four influencing parameters, namely the bottom slope, the water depth, the incident short-wave peak period and the incident group period, are shown to impact, each in a specific way, the bound wave phase lag. While the latter is seen to increase with lower water depths and/or with higher short-wave peak periods, both the bottom slope and the group period can affect the phase lag in a different manner. Indeed, steeper bed slopes induce lower phase lags in shallow water but higher ones in deep water, while higher group periods induce higher phase lags for gentle slopes but lower ones for steep slopes.
Implementation strategy of integrated coastal development in national capital city Jakarta, Indonesia
National Capital Integrated Coastal Development (hereinafter called NCICD) is one of the national strategical programs in Indonesia. The main purpose of this program is to countermeasure flooding from sea side and river side. Jakarta sinks down overtime due to land subsidence, the rate of land subsidence is various spatially 2-20 cm/year and in average the rate is around 7 cm/year. The long term planning of the coastal development for Jakarta is a compulsory to be conducted. There are three staging program of NCICD; (1) Phase-A and Phase-Emergency, here in after Phase-E, are the first phase for the critical area, where the coastal dike 120 km in total constructed along the coastline and the downstream area of the river, besides that in this phase the 13 polder system are also considered to be constructed ; (2) Phase-Midterm is the coastal dike constructed shift to the sea for near shore storage purpose; (3) Phase-Optional is the offshore sea dike construction in Jakarta Bay. The NCICD Program itself has two main scenarios for the staging. First scenario is E-A-O scenario and the second scenario is E-M-O scenario. This paper discusses the consideration of the scenario option in term of technical and financial aspects. According to the implementation strategy analysis, the E-A-O scenario is the preferable option scenario for the implementation strategy of NCICD Program if the land subsidence can not be stopped. The consideration of the scenario option, because the E-A-O scenario is cheaper than E-M-O scenario. However, if the land subsidence can be stopped than scenario E-M without O will be more efficient. In order to monitor the land subsidence, the monitoring system is deployed spatially. Nowadays, the Government of Indonesia will accelerate the surface water provision to compensate the land subsidence and issue the law enforcement to regulate the ground water abstraction after water supply distributed, even though the excessive of groundwater abstraction is one of the factor in land subsidence. In addition, the water quality improvement is also conducted parallelly.
Determining the relation between groundwater flow velocities and measured temperature differences using active heating-distributed temperature sensing
Active Heating-Distributed Temperature Sensing (AH-DTS) has the potential to allow for the measurement of groundwater flow velocities in situ. We placed DTS fiber-optic cables combined with a heating wire in direct contact with aquifer sediments in a laboratory scale groundwater flow simulator. Using this setup, we empirically determined the relationship between DeltaT, the temperature difference by constant and uniform heating of the DTS cable and the background temperature of the groundwater system, and horizontal groundwater flow velocity. Second, we simulated the observed temperature response of the system using a plan-view heat transfer flow model to calibrate for the thermal properties of the sediment and to optimize cable setup for sensitivity to variation in groundwater flow velocities. Additionally, we derived an analytical solution based on the heat flow equation that can be used to explicitly calculate flow velocity from measured DeltaT for this specific AH-DTS cable setup. We expect that this equation, after calibration for cable constitution, is valid for estimating groundwater flow velocity based on absolute temperature differences measured in field applications using this cable setup.
Geotechnisch onderzoek slibvangput Loosdrechtse Plassen : factual report
Grain size fractionation by process-driven sorting in sandy to muddy deltas
Modern and ancient analogues are often consulted by geologists to help understand subsurface systems. While modern analogues provide information on the areal relationship between facies, ancient systems provide detailed data on the vertical facies variations, typically along a two-dimensional outcrop. Combining data from modern and ancient systems effectively requires translating areal morphology, which is often still evolving, to the related sediments preserved in three dimensions. Process-based models simulate both depositional processes while preserving stratigraphy. These models can be employed to unravel the relationship between sediment supply and preserved deposits in natural systems and to help integrate field data. Four synthetic deltas were modelled using different sediment supply compositions, from coarse to very fine sand systems. The resultant sedimentary deposits are classified into architectural elements, and the grain size composition of each architectural element is studied over time. Facies that are extensive in their horizontal dimensions are often less abundant in three-dimensional preserved deposits. Between deltas, grain size composition of a specific architectural element type (e.g. mouth bars) are more similar than their corresponding sediment supply compositions. This is due to selective deposition of grain size classes across each architectural element type. This selective deposition causes overrepresentation of the same range of grain sizes, even for systems with different sediment supply compositions. When a particular supply composition does not contain enough of the overrepresented grain size class for a particular architectural element, that element will be under-supplied and constitute a smaller proportion of the overall delta deposits. It is imperative to account for over-representation of grain size classes in particular architectural elements when estimating palaeo-sediment supply, delta architecture and morphology from field data. Even when data availability/accessibility does not allow the inclusion of distal deposits in field studies, process-based simulations can contribute valuable information on sediment sorting patterns in three dimensions.
Initiation of backward erosion piping in uniform sands
The process of backward erosion piping poses a threat to dams and dikes on foundations of nonplastic sands and silts. The available models for design and predictions focus predominantly on the progression of the pipe. However, sand boils in the field will occur as a result of the initiation of sand transport. Although criteria are available for predicting sand boiling and heaving in columns, there is no model describing the initiation of piping in situations where the exit flow is not uniform, as is the case in most backward erosion experiments and situations in the field. This study compared laboratory experiments in which the process of initiation leads directly to failure with analytical and numerical groundwater flow calculations and heave criteria. The aim was to develop a model for the onset of pipe formation. It emerged that the sand bed needs to be fluidised over a distance of at least 20 times the grain diameter from the toe of the structure for a pipe to initiate. The proposed model explains the scale effects of grain size and configuration on a critical gradient. This approach clarifies the processes governing pipe initiation and progression and it can be used to establish a conservative estimate of the critical head in uniform sands, which is essential for laboratory work on this topic and for the appraisal of sand boils in practice.
Developments in modelling of backward erosion piping
One of the failure mechanisms that can affect the safety of a dyke or another water-retaining structure is backward erosion piping, a phenomenon that results in the formation of shallow pipes at the interface of a sandy or silty foundation and a cohesive cover layer. The models available for predicting the critical head at which the pipe progresses to the upstream side have been validated and adapted on the basis of experiments with two-dimensional (2D) configurations. However, the experimental base for backward erosion in three-dimensional (3D) configurations in which the flow concentrates towards one point, a situation that is commonly encountered in the field, is limited. This paper presents additional 3D configuration experiments at two scales with a range of sand types. The critical gradients, the formed pipes and the erosion mechanism were analysed for the available experiments, indicating that the erosion mechanism is more complex than previously assumed, as both erosion at the tip of the pipe (primary erosion) and in the pipe (secondary erosion) are relevant. In addition, a 3D configuration was found to result in significantly lower critical gradients than those predicted by an accepted calculation model calibrated on the basis of 2D experiments, a finding that is essential for the application of the model in the field.
32nd Symposium on the Application of Geophysics to Engineering and Environmental Problems 2019 - SAGEEP 2019 : electrical methods I : short abstracts (Portland, Oregon, 17-21 March 2019)
PVC membrane detection using ERT : modeling and laboratory experiments
PVC membranes are applied in the subsurface in infrastructural works, for example to prevent groundwater leakage. When the structure has to be adapted to changing conditions, the position of the PVC membrane needs to be known to reduce the risk of damage during the reconstruction works. So far, no “off-the-shelf” method is available to detect the position of the membrane with sufficient accuracy (0.1-0.2 m). Deltares is developing a method for the Ministry of Infrastructure, Rijkswaterstaat based on Electrical Resistivity Tomography (ERT).