Study of the Runoff Depth and Its Processes of Eucalyptus Plantations Natural Watersheds

The runoff and runoff process of Eucalyptus plantations natural watersheds were studied to provide guidance for scientific evaluation of water conservation capacities of Eucalyptus plantations, compared with the Pinus massoniana forest natural watersheds. The runoff volume of Eucalyptus plantations and P. massoniana forest natural watersheds were continuously monitored using the small watershed runoff monitoring method and the automatic data collection devices from August, 2013 to December, 2015, and effects of heavy rainfall and continuous rainfall on the runoff process were studied. Results show that the annual runoff coefficient of Eucalyptus plantations natural watershed were 0.046, and 55.8% lower than P. massoniana forest (0.104), with the difference being significant (P<0.01). The runoff duration, time lags, maximum runoff of rainfall, and runoff depth amounts caused by a heavy rainfall process (amounting to 65.5 mm) between the two kinds of forest watershed were significant different, those of Eucalyptus plantations were 8.5 h, 25 min and 2.69 mm, respectively, while those of P. massoniana forest were 18.4 h, 55 min and 5.52 mm, respectively. Eucalyptus plantations natural watershed produced only 4-days runoff, and runoff depth amounted to 3.8 mm with a 7 days continuous precipitation process of rainfall with 125.0 mm, while P. massoniana forest produced continuously 13-days runoff, and the runoff depth was 10.1 mm. In conclusion, water conservation capacity of Eucalyptus plantations is obviously lower than P. massoniana forest.