Sediment measurement in the Yellow River

This paper provides a general review of the development of sediment measurement networks on the Yellow River. Long term systematic data collection has provided information on the location of the main source area of sediment yield and on the quantity of sediment transported, deposited and diverted. Particular features of sediment laden flow at hyperconcentration are noted. A network of basic hydrometric stations together with a number of experimental stations were used to study the sediment problems. Systematic sedimentation surveys in reservoirs and in the Lower Yellow River have been used to study the fluvial processes. The aggradation and the rapidly changing pattern of the alluvial channel of the Lower Yellow River have exerted an important influence on the measuring techniques and the data processing. This paper discusses the main features of the sediment measuring techniques and a preliminary analysis of the reliability of the data. Mesure du transport solide du Fleuve Jaune RESUME Cet article expose l'organisation des observations du transport solide dans le Fleuve Jaune. D'après des observations à long terme, on a trouvé les zones d'origine du transport solide et les masses de sédiments transportés, déposés et échappant au lit principal et on a déterminé les caractéristiques de l'écoulement chargé en sédiments avec une très haute concentration en sables et limons. Pour étudier le problème des sédiments une approche efficace consiste à établir des stations hydrométriques de base auxquelles sont associés un certain nombre de stations expérimentales, et, à effectuer systématiquement des mesures topographiques dans les réservoirs et dans le Fleuve Jaune lui même pour en étudier les variations du lit. Le chenal sur le cours inférieur du Fleuve Jaune est facilement colmaté et il se modifie beaucoup et rapidement, les conditions de l'écoulement de l'eau et des sédiments sont très variables en fonction des saisons. Ceci a une très grande influence sur la technique des mesures et le traitement des données. Cet article discute les caractéristiques principales des mesures de sédiments et présente une analyse préliminaire de la validité des résultats. 275 276 Long Yuqian & Xiong Guishu THE HYDROMETRIC NETWORK The Yellow River is well known throughout the world for its exceedingly high sediment content. Historical records show that people living in the Yellow River basin have long made observations on sediment concentration. In the historic literature of the Eastern Han Dynasty (25-220 AD), descriptions of sediment content such as "the silt occupied six tenths of the volume in one barrel of water sampled" have been recorded. In the Song Dynasty, about 900 years ago, the breaching of the levee was explained by the backing up of the water surface elevation due to excessive accumulation of sediment in the river reaches downstream. It was, however, only 60 years ago that hydrometric stations based on modern scientific knowledge were established. After a rare flood which occurred in 1933, a number of hydrometric stations had been set up, however, prior to 1949, only 33 stations were collecting records. Not only was the number of stations far from adequate, but the records were also insufficient and inaccurate. Since the founding of New China, hydrological work has rapidly developed. At present, 456 hydrometric stations have been set up to make measurements all the year round. A network has been developed consisting of basic hydrometric stations supplemented by experimental stations. A great deal of valuable data have been collected, providing an important basis for the development and management of water resources as well as the development of our national economy. The Yellow River drains an area of 752 000 km, and the main stem is 5464 km in length (Fig. 1). Total annual runoff at the Fig. 1 The Yellow River drainage basin. Sanmenxia station amounts to 43.1 x 10 m, of which 58% comes from the upper portion of the basin above Hekouzhen. Large floods are mainly produced by rainstorms during July and August. The total annual sediment load averages 1.6 x 10 t and 90% of the total sediment comes from 40% of the total drainage area the middle section of the Yellow River which is overlain by loess. The Yellow River is characterized by a very high sediment load and Sediment measurement in the Yellow River 277 only a relatively limited volume of water. The hydrometric network has been developed mainly for water resource development and is not uniformly distributed. In the middle portion of the basin, a density of five to seven hydrometric stations and 40-60 raingauges per 10 000 km is found, while a density of only two to three stations and less than 10 raingauges per 10 000 km is found in the upper basin. Sediment is measured at most of the hydrometric stations. In the gullied hilly loess region of the Middle Yellow River drainage basin, the Chaba Gully experimental basin with an area of 187 km has been chosen for a study of storm runoff and sediment generation. Within the basin, nine hydrometric stations have been set up. Measurements of runoff have also been made on 14 experimental plots within a 0.18 km experimental area. Soil moisture, évapotranspiration, water balance and meteorological data have also been collected. All of these observations have provided valuable data for improving the understanding of the physical basis of soil erosion as well as surface runoff production within the study region. In order to study rates of reservoir deposition, systematic reservoir surveys have been undertaken in a number of large and medium-sized reservoirs several times per year. The inflow and outflow of water and sediment are measured at hydrometric stations. Special phenomena such as density currents, bank stability, groundwater in the vicinity of the reservoir, density of reservoir deposits and flow conditions in the vicinity of the dam have also been observed. These provide a better understanding of the physical laws of sediment movement and deposition in reservoirs. According to the seasonal variation of water and sediment inflow and the boundary conditions of the reservoir, various strategies have been developed for the planning, design, operation and management of reservoirs built on sediment-laden rivers. These have proved important in the development of water resources in the Yellow River. As an example, the general layout of the sediment survey undertaken in the Sanmenxia Reservoir is illustrated in Fig. 2. On the basis of the channel pattern, the Lower Yellow River may be divided into four sections, namely wandering, transition, meandering and estuary (Fig. 3). Eight hydrometric stations have been set up to measure the water and sediment discharge along the river course and 101 sections are surveyed repeatedly each year. Experimental stations have been established in order to study fluvial processes and the transport capacities within certain representative reaches. Hydrometric stations have also been set up at large canal headworks. Routine measurements are supplemented by reconnaissance investigations to determine the total quantity of water and sediment withdrawn for irrigation. Hydrological reconnaissance is an important supplement to the routine daily measurements made at fixed stations. It has been used extensively in the investigation of the distribution of rare storms, the peak discharge of rare floods, minimum flows, the detention effect of check dams, the use of irrigation water and erosion and sedimentation associated with structure failure. In summary, for a better understanding of sediment processes, 278 Long Yuqian & Xiong Guishu Legend 9 V t f V <""