Tingwu Lei

Modified CN Method for Small Watershed Infiltration Simulation

AbstractInfiltration is an essential process in watershed hydrology. The curve number (CN) method has been widely used to calculate watershed infiltration for a given rainfall input but does not consider steady infiltration. This study develops a modified CN (MCN) method that included a term for the steady infiltration amount (Fc). Observed rainfall–runoff data for 14 rainfall events from a typical small watershed on the Loess Plateau of China were used to derive the watershed final infiltration rate (fc). Watershed infiltration after runoff initiation was then calculated by both the MCN and CN methods using initial abstraction values that were either observed (Ia−obs) or calculated (Ia−0.2u2009u2009S) based on the calibrated fc. Three criteria [relative error (Er), model efficiency coefficient (E), and root mean square error (RMSE)] and visual assessments of graphed results were used to evaluate the methods’ simulation performances. The MCN method generally outperformed the CN method when using either of the ini...

Water use efficiency of a mixed cropping system of corn with grasses

A new cropping system of corn mixed with grasses was tried to make full and efficient use of water and to ease environmental problems such as soil erosion by water and wind in grain and forage feed production practices. Field experiments were conducted to investigate the water use efficiency under this mixture cropping system. Six treatments with two replicates were arranged as: bare field, corn only, rye only, alfalfa only, rye–corn mixture and alfalfa–corn mixture. Lysimeters were used to measure different components of water consumption in the crop fields for water use efficiency estimation. From the yields and water consumption of crops under different treatments, combined water use efficiency of corn and grasses were estimated. The results showed that WUEs in the mixed cropping fields of corn–grasses were much higher than those in the fields where only corn or grass were grown. Averaged WUE was 3.71 kg/m3 from the corn and rye mixture fields, 30% higher than that from the plots where only corn or rye were grown. Averaged WUE was 4.55 kg/m3 from the alfalfa and corn mixture fields, 60% higher than that from the fields where only corn or alfalfa were grown. Under the same conditions of irrigation, yields from the rye and corn mixture plots increased by 33%, as compared with those from fields where only corn or rye were grown. The yields from alfalfa and corn mixture fields were 61% higher than those from fields where only corn or alfalfa were grown. The experimental results also indicated that corn and alfalfa mixture cropping is better than a corn–rye mixture system.

Event-based Runoff and Sedimentation Processes from Two Watersheds of Different Land Uses on the Loess Plateau

Understanding of temporal runoff processes under different land use is of great importance for soil and water conservation practice on the Loess Plateau at watershed scales. There are two parallel Loess Plateau watersheds with the same terrain, rainfall condition, soil category and proportion, one under different erosion control measures (Qiaozi-East Watershed) and the other as control (Qiaozi-West Watershed). Terrain difference was analyzed by using GIS and the runoff process data were optimized with interpolation method by using Matlab. The result indicated that the soil and water conservation management reduced soil and water loss, the sediment reduction was better than runoff reduction. The relationships between runoff depth and erosion modulus were fitted with proportional equations at Qiaozi-East and Qiaozi-West watersheds. Soil and water conservation management changed the coefficients of the proportional equations but no format. Soil and water conservation management affected the dynamic processes of runoff, sediment content and sediment transport rate. The time of runoff initiation and peaking flow at Qiaozi-East watershed were later than that at Qiaozi-East watershed. The ratios of peak flow, runoff duration at Qiaozi-East watershed to that at Qiaozi-West watershed decreased gradually. To the end of the management, the sediment contents in runoff processes at Qiaozi-East watershed were low than that at Qiaozi-West watershed, and the differences in sediment content increased. The sediment transport rates of Qiaozi-West watershed were higher significantly than that of Qiaozi-East watershed. Soil and water conservation management of Qiaozi-East watershed decreased the sediment transport rate of runoff remarkably.

Water flow velocity over frozen and nonfrozen black soil slopes

College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi Province 712100, China Correspondence Tingwu Lei, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China. Email: leitingwu@cau.edu.cn

A spectral mixing algorithm for quantifying suspended sediment concentration in the Yellow River: a simulation based on a controlled laboratory experiment

ABSTRACT This study investigated the upper limit of suspended sediment concentration (SSC) with respect to the relationship between SSC and reflectance to develop an SSC remote-sensing model for the highly turbid Yellow River. An SSC quantification model was generated by using the spectral mixing index of sediments in water and sediment mixtures. In this study, laboratory experiments were made to measure the spectral curves of sediment-laden water with a high-resolution spectroradiometer. River-bed deposited sediments from two sites, one on the Yellow River at Huayuankou (HYK) and the other on the Wei River at Yangling (YL), and their sand, silt and clay particle groups were used for laboratory experiments to measure the spectral responses of sediment-laden water. The correlation analysis depicted stable correlation between SSC and reflectance at wavelengths ranging from 450 to 1000 nm, in which Spearman rank correlation coefficient (rs) for all sediments was above 0.7 while rs for the HYK natural sediment exceeded 0.9. Experimental results revealed the curves of the relationship between SSC and reflectance, up to 40 g l−1. A physical-based exponential model ( > 0.9) at each simulated Landsat band effectively interpreted the relationship between SSC and reflectance. The highest upper limit SSCs at 21 and 15 g l−1 in natural YL and HYK sediments, respectively, were observed in Landsat Band 4. A spectral mixing algorithm was used to build the model and estimate the SSC from reflectance at correlated wavelength bands. The spectral mixing algorithm can generate a uniform model that disregards the effects of sediment type by adopting the reflectance curve at the upper-limit SSC to represent the standard reflectance of sediment. This study is useful in understanding the spectral characteristic of high SSC in water and in applying remote-sensing techniques to monitor SSC in the Yellow River.

Estimation of suspended sediment concentrations from remotely sensed spectral reflectance: a field calibration for the Yellow River

The dynamic sediment distribution in large rivers with dams constructed has often been the focus of considerable attention because of their potential adverse environmental impacts. Sedimentation modeling and environmental assessment of man-made projects are often hindered by the lack of sediment measurements with spatial details. This study aimed to investigate the method used to estimate the suspended sediment concentrations (SSCs) from on-site spectral measurements. The study investigated the spectral signature of river water from the natural channel and Sanmenxia Reservoir on the Yellow River. A field spectral survey was conducted through on-site spectral measurements by using a spectroradimeter and SSC estimation by sampling. Reectance at 750 nm to 950 nm, with all correlation coefficient (r) between SSC and reectance > 0:7, seemed to be the appropriate range for SSC estimation. Simulated Landsat Enhanced Thematic Mapper Plus Band 4 (760 nm to 900 nm) was used to build the single band model for estimating SSC. The results confirmed that the exponential model based on the relationship between SSC and reectance (R2 = 0:92, root mean square error [RMSE]= 0:241 g=l) was better than the linear model between reectance and logarithm-transformed SSC (R2 = 0:90, RMSE = 0:310 g=l). We also applied the Spectral Mixing Algorithm (SMA) from the tank experiment to the on-site spectral measurements. The result showed that the SMA models performed as well as the single band exponential model (R2 = 0:86, RMSE = 0:280 g=l). However, the valid range for application was improved from 1:99 g=l to 347 g=l. This study could provide critical instructional assistance for estimating SSC directly from remote sensing data.

Study on the Model for Volume Estimation of Landslides by Using 3-D Laser Scanner in Wenchuan Earthquake Area

Abstract. Wenchuan earthquake produced massive loosen landslides, which have become the main source of earthquake added soil erosion, to threaten the ecological system recovery and the production and livelihood security of the localities. The landslides in Wenchuan Town, Sichuan Province were measured by using 3-D laser scanner. The model of relationship between their horizontal projected areas and volumes were suggested in this study. The accuracy of the scanning was 20.0A—20.0 cm at the place 200 m from the scanner. The geometry shape of landslide segmented was approximated as tetrahedron. The measurements of five typical landslides were used to calibrate a model to link landslide horizontal projected area to the volume. The model was verified by using Cyclone 6.0 software. This estimation model supplies an important basis for earthquake-added soil erosion forecast and volume estimation of earthquake area landslide by using remote-sensing image.

Accurate measurement of landslide volume and morphology in Wenchuan earthquake area with 3D laser scanner

Abstract: The moment magnitude (M) 8.0 earthquake in Wenchuan, Sichuan province, on May 12th, 2008 produced massive landslides made of rock and mud mixture, responsible for serious earthquake-added soil erosion on the impacts of rainfall and runoff. Morphological information of the landslides is needed for estimating the earthquake-added soil erosion. Accurate measurement and calculation of landslide volumes are of great importantances. Typical landslides in Wenchuan County were chosen to estimate their volumes by using 3-D laser scanner of high accuracy. Typical landslides were chosen to measure the relative landslide surface elevation. A method is suggested for the landslide geometry model and for estimating the volume and the morphology of the landslides, based on the measure data. The study established the method and procedures for measuring the volume of landslides with 3-D laser scanner, to supply a sound basis for estimating earthquake-added soil erosion.

Estimation of suspended sediment concentrations in the Yellow River by network monitoring records and satellite data

The sediment concentration in river flow is very important in monitoring of water quality, operation of the hydraulic facilities, and management of water resources. Commonly used sampling method is time consuming, labor intensive, and providing only point data at gauging station. This study is presenting a remote sensing approach to quantify suspended sediment concentration (SSC) of the high turbid flow in the Yellow River in China, where the high sediment transportation from severe soil erosion is a big environmental concern. The approach was based on public accessible satellite images and surface networking monitoring data. With the longest time series records, the Landsat EMT+ images were chosen to establish the remote sensing approach. Daily sediment records from 2 hydrological stations from 1999 to 2008 in the middle part Yellow River were associated with available satellite imaginary. The water reflectance was retrieved from the Landsat images by using an effective easy-to-use atmospheric correction method. Correlation among water reflectance at band 1 to 4, particle size of suspended sediment and SSC are analyzed to establish the SSC indices. According to the significance of relation between SSC and the water reflectance at different bands of Landsat data, regression models between SSC and water reflectance was developed. The model was calibrated by the daily sediment records from surface observation.

Scale and Land Use Effects on Simple Relationships Between Flow Velocity and Discharge Rate from Watersheds on the Loess Plateau, China

An empirical power function model of V = kQm has been used worldwide to describe the relationship between flow velocity (V, m s-1) and discharge rate for rills and open channel flows. This study used observed data from four experimental watersheds (Figure 1) on the Loess Plateau to determine the effect of watershed size and land use management on the parameters of both the power function and an alternative logarithmic function model of V = elnQ + d. The power function model better represented the flow velocity-discharge rate relationship in the unique context of the Loess Plateau conditions. The constant parameters in both model types were impacted by watershed size and land use management. The constants k and d, which represent flow velocity for unit discharge, were negatively correlated with watershed size, and were increased by soil loss prevention practices involving land use management. The exponential constants m and e, which determine the rate of change in flow velocity, were shown to be independent of the watershed scale and land use management. The study indicated that the power function model was able to express the hydraulic relationship at outlet channels of watersheds on the Loess Plateau but needed to be calibrated with locally observed data to optimize model performance.