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S. Y. Teh and H. L. Koh
estimate the retention volume required to store excess runoff on-site. Simulations
indicated that TH has the capacity to retain excess runoff on-site only for rain events
of low return periods of less than 2 years. Detailed analysis by WIN TR-55 concludes that the retention storage volume required to hold excess runoff for longer
return periods of 5–10 years must be increased by two or three times. An advanced
flood routing model SWMM is chosen for two purposes: (a) to extend flood simulation application to larger flood basins and (b) to provide detail information and flood
scenarios within the campus for fine-tuning of mitigation measures. SWMM simulation shows that TH can reduce flooding in downstream river Sg Harapan under a rain
of 2-year return period. However, under a rain with longer return periods, the lake’s
retention capacity will be insufficient. High runoffs did cause severe flooding in May
2011 and in Nov 2017. Excess off-site runoff originating from areas outside of USM
campus contributed significantly to the flood volume, thus aggravating the frequency
and intensity of flooding within the campus. Further, this off-site runoff contains high
loads of nutrients and faecal coliforms originating from the adjacent neighbourhoods,
contributing significant pollutant loads into TH. It is therefore essential to eliminate
this external input of runoffs and sewage flows from entering TH, consistent with
the basic principles of SDG 6: Clean water and sanitation. This option is currently
under consideration.
2.2.2 Water Quality Management
Over the years since its construction, TH has steadily accumulated nutrients such
as phosphorus P and nitrogen N, particularly in the sediments, causing the lake to
become eutrophic with high algae contents and wild fluctuations of dissolved oxygen (DO) level over the diurnal cycle (Mansor et al. 2004; Teh et al. 2008). As
part of ESD, a rehabilitation effort was initiated to clean up TH to a state suitable for recreational purposes. Monitoring and modelling of lake is conducted for
understanding the dynamics of eutrophication, and for planning and implementing
effective mitigation measures (Charumas 2004; Yacobi and Schlichter 2004). The
E2Algae or TUNA model was therefore developed to analyse the DO-algae dynamics in the lake. Simulations were performed to investigate proposed rehabilitation
options such as mechanical aeration and dredging of sediments. Simulation results
indicate that mechanical aeration will not solve the eutrophication problem in TH
(Fig. 3). Mechanical aeration during daytime proved to be futile, as the lake is already
DO supersaturated during daytime. Data collected and model simulations performed
indicate that the main culprit is the high phosphorus and high algae concentrations
(chlorophyll a of 330 µg L
−1 ) in the lake, both of which will not be removed nor
reduced by aerators. It may be concluded that mechanical aeration will not help much
in the case of TH. Aerators may help to increase DO levels in aquaculture ponds due
to the presence of high BOD.
A subsequent attempt was made beginning August 2010 to use mudball and effective microorganism (EM) to improve the water quality in TH, with undocumented
success (Asha et al. 2010). The comparison of the data before (2004) and after (2011)
S. Y. Teh and H. L. Koh
estimate the retention volume required to store excess runoff on-site. Simulations
indicated that TH has the capacity to retain excess runoff on-site only for rain events
of low return periods of less than 2 years. Detailed analysis by WIN TR-55 concludes that the retention storage volume required to hold excess runoff for longer
return periods of 5–10 years must be increased by two or three times. An advanced
flood routing model SWMM is chosen for two purposes: (a) to extend flood simulation application to larger flood basins and (b) to provide detail information and flood
scenarios within the campus for fine-tuning of mitigation measures. SWMM simulation shows that TH can reduce flooding in downstream river Sg Harapan under a rain
of 2-year return period. However, under a rain with longer return periods, the lake’s
retention capacity will be insufficient. High runoffs did cause severe flooding in May
2011 and in Nov 2017. Excess off-site runoff originating from areas outside of USM
campus contributed significantly to the flood volume, thus aggravating the frequency
and intensity of flooding within the campus. Further, this off-site runoff contains high
loads of nutrients and faecal coliforms originating from the adjacent neighbourhoods,
contributing significant pollutant loads into TH. It is therefore essential to eliminate
this external input of runoffs and sewage flows from entering TH, consistent with
the basic principles of SDG 6: Clean water and sanitation. This option is currently
under consideration.
2.2.2 Water Quality Management
Over the years since its construction, TH has steadily accumulated nutrients such
as phosphorus P and nitrogen N, particularly in the sediments, causing the lake to
become eutrophic with high algae contents and wild fluctuations of dissolved oxygen (DO) level over the diurnal cycle (Mansor et al. 2004; Teh et al. 2008). As
part of ESD, a rehabilitation effort was initiated to clean up TH to a state suitable for recreational purposes. Monitoring and modelling of lake is conducted for
understanding the dynamics of eutrophication, and for planning and implementing
effective mitigation measures (Charumas 2004; Yacobi and Schlichter 2004). The
E2Algae or TUNA model was therefore developed to analyse the DO-algae dynamics in the lake. Simulations were performed to investigate proposed rehabilitation
options such as mechanical aeration and dredging of sediments. Simulation results
indicate that mechanical aeration will not solve the eutrophication problem in TH
(Fig. 3). Mechanical aeration during daytime proved to be futile, as the lake is already
DO supersaturated during daytime. Data collected and model simulations performed
indicate that the main culprit is the high phosphorus and high algae concentrations
(chlorophyll a of 330 µg L
−1 ) in the lake, both of which will not be removed nor
reduced by aerators. It may be concluded that mechanical aeration will not help much
in the case of TH. Aerators may help to increase DO levels in aquaculture ponds due
to the presence of high BOD.
A subsequent attempt was made beginning August 2010 to use mudball and effective microorganism (EM) to improve the water quality in TH, with undocumented
success (Asha et al. 2010). The comparison of the data before (2004) and after (2011)