Sand mining is a growing environmental and socioeconomic concern worldwide. As urbanisation and infrastructure development continue to increase, the demand for sand has skyrocketed. When mined on or near rivers, it alters the river's pathway, eroding riverbanks, damaging housing, infrastructure and livelihoods. This thesis examines the role of sand mining in the river-delta system, by examining the influence of dredging duration, dredging intensity, location and pit size on the river delta system.

A 2-dimensional depth averaged Delft3D model is made. Here a river-delta system is modelled and run for 600 years. Over the last 100 years, different sand mining scenarios have been modelled. With varying duration, intensity, locations, and pit geometry, each of these scenarios is then analysed using various method of analyses. Though changing the dredging scenarios, changes the downstream morphology and hypothe-
sised trends—such as pit migration, increased erosion, and reduced delta growth—were partially
observed. Furthermore, in the five scenarios, dredging influenced the river-delta system in complex, non-linear ways.

Some configurations (e.g., 30-year duration, 5.0x intensity, 200 m width) led to pronounced short-term changes, but long-term outcomes returned toward control-like conditions. In general, the results highlight high internal variability and limited predictability based solely on single dredging parameters. It is recommended to include a cluster of slightly varied control scenarios in future research to distinguish the effect of dredging from the natural variability of the river. ... Read more

Deltas play an important role in the energy transition for their potential in subsurface applications like geothermal applications and Carbon Capture and Storage. During delta formation, the interplay between coupled forcings governs the internal architecture of the delta, leading to heterogeneity in the subsurface, which is critical for subsurface applications, as it affects fluid flow, heat transport and storage capacity and makes modelling essential for understanding the internal structure of the delta. This study uses the Roda Sandstone (the Roda X) as a case study, chosen for its well-preserved stratigraphy and documented lobe-sublobe hierarchy. This research evaluates whether DeltaRCM, a Reduced-Complexity Model, can produce a delta model of stratigraphy that is comparable to the Roda X, with an emphasis on the internal lobes. The research compares the modelling results from DeltaRCM with those from the existing Delft3D model and field data, using both surface and subsurface metrics. Under the parameter settings in this research, DeltaRCM generates delta models with strong channel incisions rather than distributary, lobe-like geometries, which do not resemble the lobe–sublobe hierarchy documented in the Roda X. The findings suggest that DeltaRCM requires further refinement or parameter adjustment to reproduce realistic lobe structures before it is used for subsurface applications. ... Read more

High-altitude páramo ecosystems in the Ecuadorian Andes, which serve a vital function in controlling the local water cycle, conserving biodiversity and securing the livelihoods of the inhabitants, are increasingly threatened. Climate variability, natural disasters and the growing pressure on natural resources due to extractive land use are the main driers. This study assesses the future environmental and social risks in the South Ecuadorian páramo surrounding Cuenca using a multidisciplinary approach. It focuses on hydrological change, slope instability, water quality and stakeholder conflict. Long-term in-situ observations made at the Zhurucay and Quinuas ecohydrological observatories are complemented by satellite and reanalysis data. We analyse multi-year trends in temperature, precipitation, soil moisture and solar radiation. Remote sensing data are calibrated and validated against ground measurements in order to make them applicable to data-scarce areas. This work also uses trend analysis and forecasting of time-series to identify the emerging hydro-meteorological patterns and the synthetic rainfall scenarios and spatial data sets to assess the slope instability under changed conditions. Additionally, water-quality risks related to changed runoff dynamics and potential mining activities are assessed. The study also includes an analysis of stakeholders of the mining Loma Larga project in order to examine how the differences in power, interests and perceived risks contribute to social tensions around water security and land use. The results show an increasing hydro-meteorological variability which may worsen the landslide risk and challenge the buffer capacities of páramo soils, while mining-related disturbances pose an additional threat to the water quality downstream and to the governance. This work integrates the physical science, remote sensing and social analysis in order to provide a comprehensive framework for understanding the coupled human-environment risks in the páramo systems. The finding may help policymakers navigate these trade-offs to support informed decision-making and ecosystem-based approaches to hazard mitigation in fragile high-mountain landscapes.
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Predicting and modelling meandering river migration is necessary for river engineering, land development, and risk assessment. One chaotic process that makes predicting the migration more difficult is the cutoff of a river bend, which is the subject of this report. This report describes the research process and results of a study on overbank flood effects on chute and neck cutoffs in single-thread meandering alluvial rivers. The following research question is addressed in this report: “What is the relationship between the duration of overbank flooding and the formation of chute versus neck cutoffs?”. The relationships between the overbank flood shear stress and the frequency of chute versus neck cutoffs, and between the soil type of the floodplain and the frequency of chute versus neck cutoffs are evaluated.

An overbank flood exceeds the bankfull limit of a river, flowing over the floodplain. When a river bend is cut off, two cutoff types are visually distinguished: neck cutoffs and chute cutoffs. Cutoffs of both types were analysed in four rivers in the United States of America: Cheyenne River in North Dakota, Powder River in Wyoming and Montana, Pearl River in Mississippi, and Trinity River in Texas. These rivers have a chute cutoff regime, a mixed cutoff regime, and two neck cutoff regimes, respectively.

For these four rivers satellite imagery on Google Earth Pro was combined with measurements from USGS measurement stations and soil data from SoilWeb. The bankfull river discharge was converted to bankfull river depth to calculate the overbank flood heights and the overbank flood shear stresses acting on the floodplain during floods. Subtraction of the critical shear stresses of the soils resulted in residual shear stresses. These were combined with the corresponding flood durations to calculate the flood impulses of each flood.

The floods associated with chute cutoffs showed larger overbank flood shear stresses than those for neck cutoffs. Rivers with steeper slopes seem to be more prone to a chute cutoff regime than rivers with gentler slopes. The soils in which chute cutoffs were formed contained high sand percentages, while the neck cutoffs occurred in a wider range of soil types. The overbank floods creating chute cutoffs exerted larger residual shear stresses for shorter durations, as opposed to smaller residual shear stresses for longer durations of floods associated with neck cutoffs. The overbank flood impulses associated with chute cutoffs show a larger range and higher values, but are on average not significantly different to those of neck cutoffs.

The processes related to river bend cutoffs are very complex and not entirely understood yet and more research is needed on a local and a greater scale. The formulation of general relationships for chaotic events such as cutoffs will improve the prediction and modelling of meandering rivers. This will be increasingly useful, especially now with more extreme weather events and river floods all over the world. ... Read more