Print Email Facebook Twitter Water Quality Modelling for Gardens by the Bay, Singapore Title Water Quality Modelling for Gardens by the Bay, Singapore Author Pijcke, G. Contributor Van de Giesen, N.C. (mentor) Heemink, A.W. (mentor) Schoups, G.H.W. (mentor) Babovic, V. (mentor) Bayen, S. (mentor) Mynampati, K.C. (mentor) Faculty Civil Engineering and Geosciences Department Water Management Programme Water Resources Date 2014-05-28 Abstract The water quality of a 5 hectare lake system in Gardens by the Bay, Singapore is modelled. The lake system comprises two lakes, Dragonfly and Kingfisher Lake, connected by a 5 metre wide stream. Inflow is from runoff from the 50 hectare catchment and from pumping from the neighbouring Marina Bay Reservoir at a rate of 20 Ls-1, 24/7. Outflow is through the irrigation offtake in Dragonfly Lake and by excess overflow from Dragonfly Lake to Marina Bay Reservoir. Monitoring and modelling of the water quality of the lakes is important for reasons of ecological sustainability, public health concerns and aesthetic purposes. Water quality data for external inflows was collected by direct measurements for temperature, dissolved oxygen, salinity, electronic conductivity and turbidity in the field and through collection of water samples for the analysis of chlorophyll-a and total phosphors concentrations by colorimetry and determination of total nitrogen, nitrite, nitrate and phosphate concentrations by ion chromatography. The data was collected during three dry and three wet events at seven point-source and five non-point source locations in the period 26 November 2013 to 06 January 2014. Nutrient inflows into the lake system in Gardens by the Bay range between 2 and 20 mgL-1 for total nitrogen and 0.05 and 1.7 mgL-1 for total phosphorus and are well above threshold values for total nitrogen (1.0 mgL-1) and total phosphorus (0.06 mgL-1) by Singapore’s Public Utility Board (PUB). The inflow of nutrients is approximately equally divided over inflow from the Marina Bay Reservoir and catchment inflows. Non-point sources contribute approximately 40% of the total phosphorus and total nitrogen load in [kg yr-1] and [kg yr-1ha-1] associated with the catchment runoff (that is excluding inflow from Marina Bay Reservoir). Point sources contribute the remaining 60% of the load from the catchment for total phosphorus and total nitrogen. The water quality model represent the water column temperature well with Root Mean Squared Error of 0.38 oC in Dragonfly Lake and 0.63 oC in Kingfisher Lake and Nash-Sutcliffe Efficiency of 0.73 and 0.72 respectively. Due to the use of average concentrations as model input values, fluctuations in the concentrations for dissolved oxygen, chlorophyll-a, total nitrogen and total phosphorus are not well captured by the model. Concentrations for water quality variables in Kingfisher Lake and Dragonfly Lake are in space. Vertical concentration differences for the modelled variables at the deepest location (4 metres) in Dragonfly Lake are highest for dissolved oxygen, 0.20 mgL-1, and chlorophyll-a, 0.37 µgL-1. An increase of the total nitrogen by 1.3 mgL-1 and total phosphorus concentration by 0.15 mgL-1 from the Marina Bay Reservoir leads to a response of corresponding magnitude in Kingfisher Lake and a an increase that is three-fold smaller in Dragonfly Lake. The same holds for a reduction of the concentrations for total nitrogen and total phosphorus. Kingfisher Lake strongly responds to changes in the characteristics of this inflow location; the water quality in Dragonfly Lake is influenced more by other catchment inflows. The combination of observation data and model data show there is a net inflow of nutrients in the lake system in Gardens by the Bay and show nutrients are accumulating in the biomass and sediment in Gardens by the Bay. Further studies should verify the nutrient loads from subcatchments through comparison of land-use types and fertilizer application in the Gardens. Sediment sampling will be required to verify the magnitude and rate of nutrient accumulation in the sediment layer. The sensitivity of the model to time-varying input data can be assessed by using the data collected for individual events rather than the average values. The three dimensional model can be simplified to a two-dimensional model. More extensive studies should indicate whether a further simplification of the model in which Dragonfly and Kingfisher Lake are represented as two fully mixed reservoirs is possible. Subject Gardens by the BaynutrientsSingaporewater quality (modelling) To reference this document use: http://resolver.tudelft.nl/uuid:aafa8936-35b5-41c7-b294-26c72860feec Part of collection Student theses Document type master thesis Rights (c) 2014 Pijcke, G. Files PDF MScThesis_GBTB_GPijcke_1504797.pdf 5.96 MB Close viewer /islandora/object/uuid:aafa8936-35b5-41c7-b294-26c72860feec/datastream/OBJ/view