Hydrology Monitoring Programme
After the heavy rain and consequent flooding incident at Lai Chi Wo in May 2014, a HKU’s cross-departmental working group has been formed with the scholars from Civil Engineering, Biological Sciences, Geography and Social Sciences (the project team). A study on the hydrology and the physical environment in the Lai Chi Wo drainage basin was proposed. A numerical hydrological model for Lai Chi Wo’s water management will be developed for tackling flooding and potential seasonal drought. The objectives of the study are:
- To study the severities (namely, return periods) of different rainfall intensities for different durations
- To apply a hydrological model to the Lai Chi Wo drainage basin
- To explore the relationship between rainfall and streamflow
- To evaluate the water resources in the catchment
Rain gauges, weather station and water level sensors have been installed in Lai Chi Wo to collect the necessary data. Several surveys were conducted to measure streamflow velocity and cross section area.
Lai Chi Wo catchment boundary, elevation data, and locations of rain gauges and water level sensors
A hydrological model, TOPMODEL, was used to simulate streamflow processes in the area and the model parameters were calibrated according to actual streamflow records. Calibration of TOPMODEL parameters is an essential process, which ensures that the simulation streamflow closely predicts observed flows. Due to lack of historical observations, only one storm event that occured between the 20th and 21st of May, 2015, was chosen to calibrate parameters.
The calibrated parameters were used to simulate long period streamflow (1985-2013) at a 5-min time step. The highest annual peak discharge simulated for the LCW catchment was 6.83 m3/s on the 19th July 1997. The peak discharge for 2, 3, 5, 10, 20, 50, 100 and 200 years return period were estimated by the Gumbel distribution method.
Flood frequency distribution for Lai Chi Wo (1985-2013)
Flood event occured on May 2014 was simulated using TOPMODEL. Simulated peak discharge is 2.99 m3/s which is the eleventh highest discharge. The return period of this event is about 3.5 years.
A hydrological model, TOPMODEL was used to simulate streamflow processes in the area and the model parameters were calibrated according to actual streamflow records. Calibration of TOPMODEL parameters is an essential process, which ensures that the simulation streamflow closely predicts observed flows.
The observed rainfall and streamflow in the LCW catchment occurred on 6-7 June 2016 and the range of the uncertainty bounds of 5% and 95% confidence intervals of the TOPMODEL simulations using GLUE method
The calibrated parameters were used to simulate long period streamflow (1985-2014) at a 5-min time step. The highest annual peak discharge simulated for the LCW catchment was 46.25 m3/s occurred on 25 July 2012 and the return period is 42.9 years. The peak discharge for 2, 3, 5, 10, 20, 50, 100 and 200 years return period were estimated by the Gumbel distribution method.
The relationship between the frequencies and discharges of the floods in the LCW catchment
Flood event occurred on May 2014 was simulated using TOPMODEL. Simulated peak discharge is 28.0 m3/s, and the related water level is about 2.20 m. This peak discharge is the fifth largest discharge for the period from 1985 to 2016. The return period of this event is about 7 years.
Simulated hydrograph for storm event occurred between 10th and 13th May, 2014
With the initial data collected from Lai Chi Wo, HKU has been granted government fund to conduct a bigger scale research to study the impact of suspended sediment, turbidity and streamflow conditions on river biodiversity in the Lai Chi Wo catchment. The specific goals are: (1) to understand the links among suspended sediment, water turbidity and river biodiversity, (2) to comprehend the relationship between flow conditions (high flow during the wet season and low flow during the dry season) and river biodiversity, and (3) to examine the influence of agricultural activities on suspended sediment and turbidity at LCW. [Read more]
Xu, Q., Chen, J., Peart, M.R., Ng, C., Hau, B.C.H. & Law, W.W.Y. (2018). Exploration of severities of rainfall and runoff extremes in ungauged catchments: A case study of Lai Chi Wo in Hong Kong, China. Science of the Total Environment. 634, 640–649.
The paper presents a systematic simulation method that is able to project the severities of flood extremes in Lai Chi Wo. A numerical hydrological model was calibrated using rainfall and stream flow data collected on-site at Lai Chi Wo. The findings could inform the possibility and frequency of flood extremes for better farm and village planning work in order to reduce risks to farmers and villagers. This systematic method would also be applicable to other ungauged catchments in the world having similar flood conditions.