Analysis of Runoff into Reservoir Change Pattern and Causes in Fenhe Reservoir

Based on the 58 years monthly flow data (from 1956 to 2013) editing by Jingle hydrological station of Fen River and Shangjinyou station, data resources are used to analyze the annual and inter-annual changes from spatial and temporal scale by statistical methods, mainly annual spatial and temporal distribution, trend of inter-annual changes, cycle and mutation changes. The reasons of runoff into reservoir changes are deeply analyzed by annual precipitation data of catchments above Fenhe Reservoir 1956 to 2013 and the land and water reservation methods which are implemented recently. It shows that there is a significant decrease of the inter-annual run-off with main and second cycle periods, 23a and 13a respectively. Furthermore, it exists mutation point between 1970 and 1971 through runoff series. As for further analysis of the causes of Fenhe Reservoir runoff changes, it illustrates that the change of precipitation is the main reason the facilitate runoff changes. Also, the land and water reservation methods which are implemented in upstream of Fenhe Reservoir increase water storage capacity of soil, showing it non-ignorable effect to runoff changes.

Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Loess Plateau Gully Region, China

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion.Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data(1981–2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation(SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997,respectively. Compared with that in the baseline period(1981–1996), annual runoff and annual sediment yield in the change period(1997–2012)decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff(137.9%) and annual sediment yield(135%) and were more important than precipitation. Biological measures(forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures(terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau.

Changes in runoff and eco-flow in the Dongjiang River of the Pearl River Basin, China

The Dongjiang River, one of the tributaries of the Pearl River, serves as the critical water source for Guangdong Province and the District of Hong Kong in China. In this study, the change trend and change points of flow at three main gaging stations in the Dongjiang River were analyzed using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. Flow regime changes in the Dongjiang River were quantified by using both the Indicators of Hydrologic Alteration （IHA） parameters and eco-statistics, such as ecosurplus and eeodeficit. It was found that the change trend for annual median flow in the Dongjiang River increased over the past 60years, with the major change occurring sometime between 1970 and 1974. IHA analyses showed that the magnitude of monthly flow decreased during the flood period, but increased greatly during the dry period. The median date of the one-day minimum flow moved ahead, and the duration of low pulse for the Dongjiang River was reduced significantly because of reservoir construction and operations. The IHA-based Dundee Hydrological Regime Alteration Method analysis indicated that all three stations have experienced a moderate risk of impact since 1974. The eco-statistical analyses showed that the majority of the flows appeared to be ecosurplus at all three locations after 1974, while flows with less than 30%, or higher exceedance probability, had ecodeficit in the summer flood period due to heavy reservoir operations.