Weimin Bao

Real-Time Equivalent Conversion Correction on River Stage Forecasting with Manning’s Formula

Channel geometry can affect the performance of the autoregressive (AR) model on river stage correction. To evaluate the effect, three ideal models were established by using the one-dimensional (1D) hydrodynamic model with imagined sets of data in assumed channels (i.e., rectangle, V-type, and complex type). To evaluate the performance of the AR model on river stage and discharge correction in a real system with unavailable observed discharges, an equivalent conversion technique by using the Manning’s formula was proposed to convert stages into equivalent conversion discharges. The results from the ideal models and real systems in the Fuchun River show that the AR model performs better on river discharge correction than on river stage correction, which is also verified at Shaowu station in the Minjiang River with available observed discharges. It indicates that the correlation of discharges is better than that of river stages. To transform corrected discharges to corrected stages, a transformation techniqu...

Differences in oxygen-18 and deuterium content of throughfall and rainfall during different flood events in a small headwater watershed

Inter-storm stable isotopic values of rainfall and throughfall for three flooding events were measured during the period of July to August 2011 to estimate their differences in a first-order chestnut watershed, Meilin, within the Taihu Lake basin. Comparison of δ2H and δ18O was conducted from four aspects: (1) sampling methods, (2) calculation methods, (3) stable isotopes and (4) flood events. Arithmetic and weighted incremental values of throughfall were generally lighter than those of rainfall. Isotopic composition of both incremental rainfall and throughfall exhibits marked temporal variation, particularly during large storm events; the former shows a higher variation than the latter. Differences of averaged precipitation and throughfall between storms were small, but individual storm variations were larger. Isotopic differences using different calculation methods are not significant; however, the differences resulting from sampling methods are of greater importance.

Efficient Calibration Technique under Irregular Response Surface

AbstractConceptual rainfall-runoff models that aim at predicting streamflow from the knowledge of rainfall over a catchment are a basic tool for flood forecasting. The parameter calibration of a conceptual model usually involves the selection of an automatic optimization algorithm to search for the parameter values that minimize the distance between the simulated and observed data. However, practical experience with model calibration suggests that traditional optimization methods, such as the Newton-Raphson, conjugate gradient, and downhill simplex methods, are easily trapped in local minimums because the objective function surface is rough, caused by model structure errors and data errors. The across-ridge calibration method (ARC), an effective and efficient methodology for searching global optimization problem, is proposed in this paper. The method searches for all local optima in a fixed boundary, which makes it less susceptible to the irregularity of the response surface. The features and capabilities...

Experimental Study on Evaporation Pan Isotopic Variations

Lake participates in water cycle through inflow and outflow of surface water and groundwater, precipitation and evaporation. Stable isotope technique is a very useful tool for studying variation of lake water. This paper briefly introduced the isotopic theory of lake, and studied the isotopic variation of atmospheric water vapor delta A through indoor and outdoor evaporation pan experiments. The experimental results showed that delta A values estimated from isotopic mass balance method were suitable to study the short-term isotopic variation of lake at time interval of six days; the slope of pan evaporation line of outdoor experiment was lower than that of indoor experiment due to kinetic fractionation factor of outdoor experiment being higher than that of indoor experiment.

Isotopic Exchange of Soil Water in Water Cycle

Environmental isotopes can be effective used for tracing water cycle and addressing water resource problems. Isotopes as natural tracers can be used to trace the transportation process of water in water cycle and the variations of isotopic value can provide information about the transference of soil water. In this paper, the variations of stable isotopes in catchment hydrological process are introduced, the isotope hydrograph separation method is reviewed, and the fundamentals of isotopic behavior in soil water are mainly discussed. An experiment on isotopic exchange between precipitation and soil water in an artificial soil trough is carried out. The results indicate that the oxygen isotopic content of the flow in the outlets changes from about −8.5‰ to −6.5‰ along with the runoff generation while the isotopic compositions of rain water are unchangeable. Therefore, the isotope exchange degree between soil water and rain water is considerable and the mutual mixing may be an important way for isotopic variations in soil water. This study has great significance to reveal the rules of transformation between precipitation and soil water.

Uncertainty Analysis of the Tracer-Based Hydrograph Separation Method

Tracer-based hydrograph separation relying on the mass balance equations of water and isotopic compositions is very appealing and widely used in basin hydrology, due to its simplicity. However, much uncertainty of this method is presented in practical applications, which is mainly affected by model assumptions. In this paper, theoretical analysis is conducted to test the reality of some fundamental assumptions involved in isotopic hydrograph separation method. The results indicate that soil water plays an important role in stormflow generation, and the previous assumption that contributions from soil water are negligible in hydrograph separation seems to be unrealistic. It shows that the bigger the contribution rate of soil water is, or the greater the difference of the isotopic compositions of soil water and base flow is, and thus the bigger the estimated error of the proportion of pre-event water is. Finally, some feasible suggestions are put forward to improve the application of the isotopic hydrograph separation method.

Discussion of Present Isotopic Hydrograph Separation (IHS) Method

Runoff sources and dominant flow paths are still poorly understood in most catchments. Consequently, isotope hydrograph separation methods are widely used to improve our understanding about runoff generation. Isotope hydrograph separation (IHS) is based on the mass balance equation of water flux and isotope tracer concentration. The isotope analysis machine (for example, mass spectrum) available can only get the δ-value of the isotope tracer. An analysis is presented for quantifying the error in two- and three- component tracer-based hydrograph separation. This analysis compared the error between ratio balance method and mass balance method in computing mixed fractions to determine which method is more accurate. In the ratio balance method, the ratio of isotope tracer in used in concentration mass balance equation; comparatively, in the mass balance method, the concentration of isotope tracer is used in the same equation. Many studies about two- and three-component tracer-based hydrograph separation are used to illustrate the application of the analysis. Because of the abundance of rare isotopes are so negligible, the difference between two methods is small in the isotopic hydrograph separation studies. In scientific research, it is not appropriate to substitute ratio for concentration in the isotope tracer concentration mass balance equation. Therefore, we recommend the use of mass balance method in the application of isotope hydrograph separation research to improve the degree of accuracy.

Study on the Variation of Hydrogen and Oxygen Isotopes in Soil Water

Understanding the movement of soil water is important for water resource management and for analyzing pollutant transport in the vadose zone. The information about transfer and transformation in soil water could be provided by isotope tracing technology. The stable isotopic composition of soil water may be affected by many factors, e.g. precipitation, surface evaporation and movement of soil water. In this paper, basic principle of isotope transformation, main influence factor and the variation process of stable isotope concentration are studied. An experiment of isotope exchange in soil columns is carried out, and the exchange and mixing processes between input water and soil water are analyzed. The results show that the isotope concentration variation of mixed water in soil columns may reach more than 20% compared to the initial input water while the mass proportion of soil water and input water is about 3:10, which indicate that the isotope exchange degree is considerable. Therefore, the mixing action between precipitation and soil water may be an important way for the isotopic variation of soil water in the basins.

Application of Stable Isotope Method in Water Mass Balance of Qinghai Lake

Inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope mass balance method. It provides a way for integrating the spatial and temporal complexities of the flow field around a lake. In this paper, the method is successfully applied to Qinghai Lake in China. Qinghai Lake located in the northeastern part of the 4,500-metre-high Qinghai-Tibet plateau, is the largest inland lake of China, therefore, it is significant to establish water balance of the lake. According to the stable isotopic value and relevant hydro meteorological data, the mean annual evaporation and groundwater inflow rate calculated for the Qinghai Lake using the isotope mass balance method are 40.9 and 6.40 hundred million stere, respectively, which compare well to measure values, of 40.5 and 6.03 hundred million stere. The results demonstrate that it is feasible for stable isotope mass balance method to estimate inflow and outflow of Qinghai Lake.