Xuefeng Chu

An environmental assessment of an impacted, urbanized watershed: the Mona Lake Watershed, Michigan

The ecological health and integrity of watersheds throughout the world are being threatened by a variety of stressors. Often, restoration practices focus on single problems whereas comprehensive, multidisciplinary approaches are needed to address both the symptoms and underlying causes of impairment. A comprehensive assess- ment of a small, urbanized watershed in west Michigan, USA was conducted to evalu- ate the major stressors in the system. This assessment approach for the Mona Lake wa- tershed included analyses of land use/land cover change, water quality in both the major surface inflows and the receiving water body, and toxic inputs into a major in- flow. Because these issues are common to many watersheds, we developed a concep- tual model that spatially links these stressors and predicted impacts, allowing us to as- sess them in a comprehensive manner. Based on our results, we generated a set of re- commendations targeted for specific source or problem areas. This approach can be applied to other watersheds.

An improved method for watershed delineation and computation of surface depression storage.

Surface microtopography plays an important role in overland flow generation and soil erosion processes. Characterization of surface depressions and delineation of the entire watershed are critical to watershed modeling and management. In most hydrologic models, however, surface depression storage is estimated indirectly and inputted as a known value. In addition, it is often assumed that overland flow initiates after all surface depressions are fully filled. In reality, surface microtopography may control overland flow generation, surface runoff, soil erosion, and other hydrologic processes in a dynamic manner. The role of depressions that have various spatial scales and distribution characteristics is far beyond the functions of storing and detaining/retaining surface runoff. In this study, an improved surface delineation method was proposed to identify surface depressions and their relationships, precisely quantify the surface microtopography, and compute the maximum depression storage based on high-resolution DEM data obtained by using an instantaneous-profile laser scanner. Furthermore, a user-friendly, Windows-based software package was developed to facilitate the associated computations and visualization. The delineation method and the related software were tested using various scale DEM data. It is demonstrated that the new delineation approach is effective and efficient.

Delineation of Pothole-Dominated Wetlands and Modeling of Their Threshold Behaviors

AbstractTime-invariant contributing area and full hydrologic connectivity are commonly assumed in traditional watershed delineation and modeling. In reality, however, contributing area of a depression-dominated prairie basin varies and undergoes a progressive evolution process that is characterized by unique threshold behaviors associated with the depression filling–spilling–merging–splitting–depleting dynamics. The research reported in this paper aims to precisely delineate prairie potholes and the associated wetlands, effectively characterize their dynamic hydrotopographic properties, and further quantify the resultant threshold behaviors and spatiotemporal variability in hydrologic connectivity. Delineation and modeling for a wetland site in the Prairie Pothole Region (PPR) highlighted the crucial role of topographic characteristics in the formation, evolution, and connectivity of prairie potholes. Particularly, the modeling tests for real rainfall demonstrated the significant impacts of complex rainfa...

IPTM-CS: A windows-based integrated pesticide transport model for a canopy-soil system

A Windows-based integrated pesticide transport modeling system (IPTM-CS) has been developed for simulating three-phase (dissolved, adsorbed, and vapor phases) pesticide environmental fate in a canopy-soil system (or in the vadose zone alone). The modeling system integrates pre-processing of data (parameters estimation and input), model run, and post-processing of simulation results (summary tables, Excel spreadsheets, and graphs) in a user-friendly Windows interface. To facilitate parameter estimation, an extensive data supporting system that includes convenient parameter calculators and databases has also been developed and incorporated in the IPTM-CS. The data supporting system also provides links to a number of web-based databases maintained by government agencies and institutions. A time-continuous and space-discrete (TC-SD) method is employed to solve the transport problem and five different solution schemes of varying accuracy and features have been incorporated in the interfaced IPTM-CS. Finally, testing of the IPTM-CS at a field site in Chico, California is presented. Comparison of the simulated and observed diazinon concentrations is conducted for three selected depths (0.15, 0.25, and 0.5m) and the results are further evaluated by using three methods (linear regression, normalized objective function, and modeling efficiency). The quantitative evaluation indicates that the IPTM-CS yields fairly good simulations.

Simulation of Infiltration and Surface Runoff - A Windows-Based Hydrologic Modeling System HYDROL-INF

Simulation of infiltration and surface runoff, two closely-correlated processes during rainfall events (wet time periods), is critical to water quantity and quality studies for both surface and subsurface systems. Partitioning rainfall into these two primary water pathways is fundamental to any hydrologic modeling. In a continuous hydrologic model, it is also essential to simulate drainage and redistribution of soil water between two rainfall events (dry time period). A new algorithm is proposed to simulate infiltration into a layered soil profile of arbitrary initial water distributions under unsteady rainfall and the resultant surface runoff. Two distinct periods, preponding and post-ponding, are taken into account. The model tracks the movement of the wetting front along the soil profile, checks the ponding status, and handles the shift between ponding and non-ponding conditions. The model is further extended to complex rainfall patterns that include both wet time periods with unsteady rainfall and dry time periods without rainfall by incorporating a compartmental model that accounts for drainage and redistribution in the soil profile. Furthermore, a Windowsbased modeling system, HYDROL-INF, is developed, which integrates preprocessing of data, model run, and post-processing in a user-friendly Windows interface. To facilitate parameter estimation, a parameter database is developed and incorporated. Additionally, the HYDROL-INF system also includes some useful hydrologic tools/calculators that can be used in applied hydrologic investigations.

Fractal Analysis of Surface Microtopography and its Application in Understanding Hydrologic Processes

Fractal analysis provides a useful way to characterize the spatial complexity of surface microtopography. In this study, six random roughness soil surfaces and two field plot surfaces were created. Anisotropic properties of these surfaces were examined by using the directional semivariogram method and a modified anisotropy index (a). Multifractal analysis was performed to identify the dissimilar changing patterns of fractal dimension (D) and crossover length (l) for these surfaces at different scales. It has been found that D and l at smaller scales describe topographic surfaces in more detail, while the overall topographic features of the surfaces can be captured by D and l at larger scales. Surface slope removal has a considerable effect on the fractal calculation using the semivariogram method. This study also demonstrates that fractal parameters D and l have clear and meaningful relationships with some hydrotopographic parameters, such as random roughness (RR), maximum depression storage (MDS), and number of connected areas (NCA). More importantly, fractal and anisotropic analyses enable better understanding of the overland flow generation process. A surface with a small D value has the potential to retain more water in its depressions, which in turn redistributes surface runoff water, enhances infiltration in depressions, and delays surface runoff initiation. The dominant roughness exists along the directions of smaller D values. Along those directions, surface runoff is prone to be hindered or blocked by ridges, while better hydrologic connections occur along other directions.

Modeling Metal and Sediment Transport in a Stream-Wetland System

It has been a challenge to couple a stream channel system with adjacent wetlands and to simulate their interactions and the dynamic processes associated with water flow, sediment movement, and contaminant transport. In this study, a physically based model was developed for simulating metal and sediment transport in a coupled stream-wetland system that consisted of the water column, the underlying active bed, and the adjacent wetland subsystems. The model simulated the dynamic interactions and mass exchanges (water, sediment, and metal) between subsystems and accounted for a set of processes related to the two-phase (dissolved and adsorbed phases) metal and sediment transport, including advection, dispersion/diffusion, sorption, settling, resuspension, and sedimentation. The integrated metal-sediment transport model was solved by using a semidiscrete method. Model simulations of cadmium fate and transport were tested against field data from Little Black Creek (LBC) in western Michigan, which was heavily im...

Sensitivity Analysis for an Infiltration-Runoff Model with Parameter Uncertainty

Evaluation of the uncertainty effect of input parameters on model outputs is presented. HYDROL-INF, an infiltration-runoff model for layered soils, is used for simulating infiltration and surface runoff. The predictive uncertainty related to the modeling is evaluated. Specifically, a three-step procedure is implemented for sensitivity analysis of the model. The first step involves application of the local sensitivity analysis to gain a qualitative ranking of the whole set of input parameters for different model outputs with a relatively low computational cost. In the second step, the first-order second moment (FOSM) method is used to obtain the most sensitive parameters to the output from the parameters identified by the local sensitivity analysis. Third, the robust and computationally efficient Fourier amplitude sensitivity test (FAST) is conducted to overcome the nonlinearity problem for estimating the uncertainty of the model. Furthermore, the proposed methodology is applied to a three-layer soil syste...

Multicriteria Evaluation Approach for Assessing Parametric Uncertainty during Extreme Peak and Low Flow Conditions over Snow Glaciated and Inland Catchments

AbstractThis paper examines model uncertainties associated with streamflow by characterizing it into extreme high (peak) flows and low flows in two different catchments, viz. a snowmelt-induced hilly catchment (Satluj) and an inland catchment (Tungabhadra). The streamflow was initially simulated and calibrated using the soil and water assessment tool (SWAT) model and SWAT CUP (calibration and uncertainty program) based sequential uncertainty fitting approach (SUFI2) by analyzing 14 different hydrological parameters. The multiple criteria evaluation was based on the multiple linear regression equations and noncommensurable measures of information derived from river flow series by means of a number of sequential time-series processing tasks, including separation of the river flow series into extreme peak flows and low-flow hydrograph periods. A reliable set of rules for model calibration was applied to all linear-regression-based objective functions. The authors found that extreme peak flow conditions were ...

Microrelief-Controlled Overland Flow Generation: Laboratory and Field Experiments

Surface microrelief affects overland flow generation and the related hydrologic processes. However, such influences vary depending on other factors such as rainfall characteristics, soil properties, and initial soil moisture conditions. Thus, in-depth research is needed to better understand and evaluate the combined effects of these factors on overland flow dynamics. The objective of this experimental study was to examine how surface microrelief, in conjunction with the factors of rainfall, soil, and initial moisture conditions, impacts overland flow generation and runoff processes in both laboratory and field settings. A series of overland flow experiments were conducted for rough and smooth surfaces that represented distinct microtopographic characteristics and the experimental data were analyzed and compared. Across different soil types and initial moisture conditions, both laboratory and field experiments demonstrated that a rough soil surface experienced a delayed initiation of runoff and featured a stepwise threshold flow pattern due to the microrelief-controlled puddle filling-spilling-merging dynamics. It was found from the field experiments that a smooth plot surface was more responsive to rainfall variations especially during an initial rainfall event. However, enhanced capability of overland flow generation and faster puddle connectivity of a rough field plot occurred during the subsequent rain events.