Canal Emilio Mitre is a navigation channel that runs through the Rio de la Plata estuary in South America. It grants access to the second largest inland waterway system in South America, covering (parts of) Argentina, Uruguay, Brazil, Paraguay and Bolivia. The channel is a main bottleneck for navigation for two reasons; the channel has a continuous need for maintenance dredging and it is only navigable during a tidal window. Furthermore, the dredging effort shows high interannual variability, resulting in risks for the contractor and users. The current study identifies the dredging effort and strategy, and a conceptual model is made of what physical processes force the sedimentation. The IPCC reports are used to identify the effect of climate change and variability on the drivers of the sedimentation. The interannual variability is shown to be linked to climate variability, due to the ENSO phenomena. The drainage basin of the Rio Parana is affected by an increase in precipitation and sediment input during El Nino events as a result of the teleconnections of ENSO. A depth-averaged numerical model (Delft3D) is set-up to address the effect of climate, deepening and wind scenarios on the dredging effort and its variability. The numerical model was validated by comparing the reported dredged volumes in the system to the simulated sedimentation. Overall, the sedimentation in the system is found to be sensitive to highly energetic events due to a redistribution of the fine sediments over the estuary. The acquired knowledge on the physical processes of the system in combination with the outcomes of the scenarios are used to make recommendations on the future dredging strategy to reduce the risk due to variability. This study highlights the importance of taking into account the risks and chances due to climate variability in dredging projects in regions affected by teleconnections with a duration of around 10 years.

Globally, growing demand for fresh water and declining water availability puts significant pressure on water resources. Due to rapid urbanization and insufficient water resource planning and waste water management, the Kathmandu Valley (Valley) is facing both a water quantity and quality crisis. Annually, groundwater extractions in the Valley significantly exceed recharge rates, resulting in a serious groundwater table declines. While streams often constitute an important linkage between surface water and groundwater systems, from both a quantity and quality perspective, understanding stream-aquifer interactions in the Valley are limited. To improve this understanding, we performed topographic surveys of water levels, and measured water quality, in streams and adjacent hand dug wells (shallow aquifer) in three watersheds (total of 16 stream-well pairs) during 2018 pre-monsoon (April and May) and eight watersheds (including the same three from pre-monsoon; total of 35 stream-well pairs) during 2018 post-monsoon (September and October). In pre-monsoon, we found 88 % of water levels in wells lower than adjacent streams with an average of -0.82 m, indicating a loss of stream water to the aquifer. However, in post-monsoon 69 % of wells had water levels higher than adjacent streams with an average water level difference of 0.44 m, indicating that monsoon rainfall recharged the shallow aquifer, causing streams to transition from losing to gaining. No recurring trend in water level difference was seen longitudinally from upstream to downstream. Our results indicate statistically significant correlations between electrical conductivity, ammonia, chloride, hardness, and alkalinity measured in streams and adjacent wells. Both stream and groundwater quality of adjacent wells depletes longitudinally from upstream to downstream. In order to prevent further deterioration of groundwater resources, stream-aquifer interactions should be taken into account for sustainable water resource management. Further research is essential to quantify the groundwater flow, and to investigate the long-term trends and reversibility of the problem. Our findings highlight the importance of managing streams and aquifers as a single integrated resource, from both a water quantity and quality perspective. For example, improper waste management in the Valley’s streams is having a clear and negative impact on the shallow aquifer. The population of Kathmandu will become increasingly dependent on the government for water supply, potentially increasing the cost of living.