Your search found 3 records
1 Terry, J. P.; Chui, T. F. M.; Falkland, A. 2013. Atoll groundwater resources at risk: combining field observations and model simulations of saline intrusion following storm-generated sea flooding. In Wetzelhuetter, C. (Ed.). Groundwater in the coastal zones of Asia-Pacific. Dordrecht, Netherlands: Springer. pp.247-270. (Coastal Research Library Volume 7)
Atolls ; Groundwater ; Water resources ; Freshwater ; Aquifers ; Salt water intrusion ; Sea level ; Flooding ; Storms ; Risk management ; Models ; Case studies / New Zealand / Cook Islands / Pukapuka Atoll
(Location: IWMI HQ Call no: 551.457 G570 WET Record No: H046336)
The restricted nature of naturally-occurring freshwater resources on atolls is one of the greatest impediments to human settlement on these small, dispersed and remote islands. Any anthropogenic or environmental pressures that deleteriously affect the quantity or quality of atoll water resources are therefore a matter of concern. This chapter focuses on such issues. It first presents an overview of the principal characteristics of atoll fresh groundwater aquifers, which exist in the form of thin lenses within the Holocene sands and gravels that comprise the sedimentary substrate of low-lying atoll islets. Factors that influence the vulnerability of these freshwater lenses are then considered. The chapter continues by summarising the findings of recent studies that investigated the effects of storm-wave washover across atoll islets on freshwater lens profiles, and the subsequent patterns of recovery over time. Both field and modelling approaches are used. Combined results suggest that following groundwater salinisation by seawater intrusion, at least a year is required for full aquifer recovery. Of particular interest, it is found that in spite of a strong saline plume forming at relatively shallow depths, a thin horizon of freshwater sometimes remains preserved deeper within the aquifer profile for several months after the initial disturbance. In the Pacific basin, shifting geographical patterns in severe tropical storm events related to climatic variability and change are a threat to the continuing viability of atoll fresh groundwater resources and the human populations dependent upon them.
2 Meshgi, A.; Schmitter, P.; Babovic, V.; Chui, T. F. M.. 2014. An empirical method for approximating stream baseflow time series using groundwater table fluctuations. Journal of Hydrology, 519:1031-1041. [doi: https://doi.org/10.1016/j.jhydrol.2014.08.033]
Stream flow ; Time series analysis ; Hydrology ; Models ; Simulation ; Water resources ; Groundwater table ; Catchment areas ; River basins ; Rain ; Soil hydraulic properties ; Case studies / Singapore / USA / Kent Ridge Catchment / Beaver River Basin
(Location: IWMI HQ Call no: e-copy only Record No: H046591)
(1.73 MB)
Developing reliable methods to estimate stream baseflow has been a subject of interest due to its importance in catchment response and sustainable watershed management. However, to date, in the absence of complex numerical models, baseflow is most commonly estimated using statistically derived empirical approaches that do not directly incorporate physically-meaningful information. On the other hand, Artificial Intelligence (AI) tools such as Genetic Programming (GP) offer unique capabilities to reduce the complexities of hydrological systems without losing relevant physical information. This study presents a simple-to-use empirical equation to estimate baseflow time series using GP so that minimal data is required and physical information is preserved. A groundwater numerical model was first adopted to simulate baseflow for a small semi-urban catchment (0.043 km2) located in Singapore. GP was then used to derive an empirical equation relating baseflow time series to time series of groundwater table fluctuations, which are relatively easily measured and are physically related to baseflow generation. The equation was then generalized for approximating baseflow in other catchments and validated for a larger vegetation-dominated basin located in the US (24 km2). Overall, this study used GP to propose a simple-to-use equation to predict baseflow time series based on only three parameters: minimum daily baseflow of the entire period, area of the catchment and groundwater table fluctuations. It serves as an alternative approach for baseflow estimation in un-gauged systems when only groundwater table and soil information is available, and is thus complementary to other methods that require discharge measurements.
3 Meshgi, A.; Schmitter, Petra; Chui, T. F. M.; Babovic, V. 2015. Development of a modular streamflow model to quantify runoff contributions from different land uses in tropical urban environments using Genetic Programming. Journal of Hydrology, 525:711-723. [doi: https://doi.org/10.1016/j.jhydrol.2015.04.032]
Urbanization ; Hydrology ; Stream flow ; Models ; Rainfall runoff relationships ; Land use ; Infiltration ; Catchment areas ; Vegetation / Singapore / Kent Ridge Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H046995)
(2.55 MB)
The decrease of pervious areas during urbanization has severely altered the hydrological cycle, diminishing infiltration and therefore sub-surface flows during rainfall events, and further increasing peak discharges in urban drainage infrastructure. Designing appropriate waster sensitive infrastructure that reduces peak discharges requires a better understanding of land use specific contributions towards surface and sub-surface processes. However, to date, such understanding in tropical urban environments is still limited. On the other hand, the rainfall–runoff process in tropical urban systems experiences a high degree of non-linearity and heterogeneity. Therefore, this study used Genetic Programming to establish a physically interpretable modular model consisting of two sub-models: (i) a baseflow module and (ii) a quick flow module to simulate the two hydrograph flow components. The relationship between the input variables in the model (i.e. meteorological data and catchment initial conditions) and its overall structure can be explained in terms of catchment hydrological processes. Therefore, the model is a partial greying of what is often a black-box approach in catchment modelling. The model was further generalized to the sub-catchments of the main catchment, extending the potential for more widespread applications. Subsequently, this study used the modular model to predict both flow components of events as well as time series, and applied optimization techniques to estimate the contributions of various land uses (i.e. impervious, steep grassland, grassland on mild slope, mixed grasses and trees and relatively natural vegetation) towards baseflow and quickflow in tropical urban systems. The sub-catchment containing the highest portion of impervious surfaces (40% of the area) contributed the least towards the baseflow (6.3%) while the sub-catchment covered with 87% of relatively natural vegetation contributed the most (34.9%). The results from the quickflow module revealed average runoff coefficients between 0.12 and 0.80 for the various land uses and decreased from impervious (0.80), grass on steep slopes (0.56), grass on mild slopes (0.48), mixed grasses and trees (0.42) to relatively natural vegetation (0.12). The established modular model, reflecting the driving hydrological processes, enables the quantification of land use specific contributions towards the baseflow and quickflow components. This quantification facilitates the integration of water sensitive urban infrastructure for the sustainable development of water in tropical megacities.
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