Numerical Study Of Saltwater Intrusion In Modaomen Of Pearl Estuary

Modaomen Estuary, one of eight major mouths, is the main estuary of the Xijiang River of the Pearl River. In the recent 10 years, the salt water intrusion in Modaomen Estuary becomes severe because of the increasing of the water demand, the decreasing of the runoff, and river bed changes and the sea level rising, which influences water supply to Macao and Zhuhai cities.Based on the statistical analysis of the salinity data with the lunar cycle during the dry season from 2003 to 2008, the salt water intrusion factor K is introduced to response the relationship between 15d-averaged discharge of the runoff Q1 5dand 15d-averaged salinity S 15d. When K<0.2, it represents saltwater less intrusion, and the salinity most of the time matches the standard of drinking water; when K>0.5, it represents saltwater seriously intrusion, and the salinity can not match the standard of drinking water; when 0.23/s for K=0.2 and 0.5.Three-dimensional hydrodynamic models for Pearl River Mouth and Modaomen Estuary were setup using EFDC Code. Computational results show good agreements with the observed data, including tide level, velocity and salinity during the wet and dry seasons. The coupling model of Pearl River and Modaomen Estuary by the domain decomposition techniques using Delft3D model is used to compare with the EFDC computational results. The computational results show that Modarmen EFDC model has good performance of the hydrodynamic conditions and salinity intrusion.The calculating result under different runoff conditions shows, when Q1 5d= 1000m³/s, K=3.87, and S 15d is more than 1000mg/L; when (Q|-)_15d= 1480m³/s, K=0.69, and there are 6d the daily average chlorinity is more than 1000mg/L; when (Q|-)_15d= 3450m³/s, K=0.005, the salinity matches the standard of drinking water. when (Q|-)_15d= 2540 and 1930m³/s, K=0.22 and 0.45, which are close to 0.2 and 0.5 according to the response curve.