Laboratory examination of linearity in rainfall–runoff relationships

ABSTRACT

Certain rainfall–runoff models, e.g. the unit hydrograph, assume linear relationships between the variables. These are proportionality of runoff discharges to (net) rainfall depth and linear summations of discharges resulting from (net) rainfalls during different time intervals or over different sectors of a watershed. This study examines the validity of these assumptions by use of an extensive two-dimensional laboratory experimentation. The results indicate that proportionality would be found under high rainfall intensity through a long duration. Spatial summations would more likely yield correct discharges in cases where rainfall duration is equal to, or is longer than, the time of concentration. Temporal summations may yield correct discharges when rainfall duration is longer than one half of the time of concentration. Here, the time of concentration is determined at the beginning of gradual approach of the discharge towards the equilibrium state.     

A study to explain the emission of nitric oxide from a marsh soil

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10^–12 kgN m^–2 s^–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.     

软土深层搅拌桩的水泥土抗腐蚀性室内试验

结合深港西部通道填海区深层搅拌桩在滨海地下水环境中施工的需要,对水泥土在自来水、地下水、海水及Na2SO4溶液环境下的抗腐蚀性进行了室内研究,研究表明以纯水泥为固化剂的水泥土在腐蚀性地下水环境中的抗腐蚀性能较差,增加矿渣、粉煤灰的含量,能增强水泥土抗腐蚀性;分析了固化剂中矿渣、粉煤灰掺入量对水泥土抗压强度及抗腐蚀性的影响规律,即固化剂掺入比不变的情况下,用矿渣、粉煤灰替代部分水泥能大幅度提高水泥土的抗压强度,同时改善其抗腐蚀性;得出了抗腐蚀性能良好的水泥土配方,即矿渣、粉煤灰的质量占固化剂的40%～60%,可供同类工程借鉴.     

Acceleration of buoyancy-driven fractures and magmatic dikes beneath the free surface

By performing buoyancy-driven fracture experiments in brittle gelatin we observe that the ascent velocity of a fracture containing a finite volume of fluid increases when approaching the free surface. We theoretically describe this free-surface effect and quantify it by introducing an effective depth-dependent fracture toughness and developing an ascent model on the basis of linear fracture mechanics. We develop a successful inversion approach and resolve the actual and critical fracture length and the ascent velocity far away from the free surface from the observation of the fracture tip migration alone. Other parameters, as the fluid volume included in the fracture and the in situ fracture toughness, can be derived. Applying the model and inversion to the 1998 eruption at Piton de la Fournaise, Reunion Island, reveals estimates of the length and critical length of the feeding magma batch, the magma batch volume and the in situ fracture toughness. It further indicates that the ascent velocity of the magma batch was probably much smaller at greater depths and that the batch might have been initiated several months or years before the eruption.     

Effect of loading rate on the volume change behavior of unsaturated residual soil

Residual soils occur in most countries of the world but those that occur in greater area and depth are usually found in the tropical humid areas. This research examines the effects of loading rate of applied or net mean stress on the volume change behavior of an unsaturated granitic residual soil. Three loading rates were adopted: fast, slow and extra slow loading rate. It was observed that the loading rate of applied or net mean stress has a pronounced effect on the void ratio and degree of saturation but has an insignificant effect on the water content of residual soils subjected to constant matric suction.     

震源物理实验室“八五”技术改造

由国家地震局地球物理研究所承担的“ＭＴＳ－１００Ｔ伺服试验机改造”课题,对震源物理实验室进行了实验系统改造。该文简要介绍了该课题所完成的主要工作及其应用情况,包括：ＭＴＳ－１００Ｔ伺服试验机控制系统、１６通道高速数据采集系统、激光散斑图干涉仪。     

The use of laboratory experiments for the study of conservative solute transport in heterogeneous porous media

 Laboratory experiments on heterogeneous porous media (otherwise known as intermediate scale experiments, or ISEs) have been increasingly relied upon by hydrogeologists for the study of saturated and unsaturated groundwater systems. Among the many ongoing applications of ISEs is the study of fluid flow and the transport of conservative solutes in correlated permeability fields. Recent advances in ISE design have provided the capability of creating correlated permeability fields in the laboratory. This capability is important in the application of ISEs for the assessment of recent stochastic theories. In addition, pressure-transducer technology and visualization methods have provided the potential for ISEs to be used in characterizing the spatial distributions of both hydraulic head and local water velocity within correlated permeability fields. Finally, various methods are available for characterizing temporal variations in the spatial distribution (and, thereby, the spatial moments) of solute concentrations within ISEs. It is concluded, therefore, that recent developments in experimental techniques have provided an opportunity to use ISEs as important tools in the continuing study of fluid flow and the transport of conservative solutes in heterogeneous, saturated porous media. Received, December 1996 · Revised, July 1997 · Accepted, August 1997     

BRDF室内实验处理系统及应用(英文)

与野外ＢＲＤＦ实验相比，室内实验更容易控制，具有无风、无云、光源固定和可全方位重复观测等优点，获取的反射率数据和测量的植被结构数据的精度要较野外测量的高，可用于ＢＲＤＦ模型验证及反演试验。     

上海老港垃圾卫生填埋场隔离墙材料特性室内试验研究

为了控制垃圾渗滤液的侧向渗透,在城市垃圾卫生填埋场四周需设置垂直隔离墙。隔离墙采用现场开挖深槽,然后在槽内灌注水泥一膨润土一砂混合浆液的方法构筑。通过室内配比试验的方法,测定不同配比试件的无侧限抗压强度、渗透系数等参数,为隔离墙的施工提供合理的配比。