城市地表径流面源污染分析研究——以武汉市典型下垫面为例

城市地表径流面源污染已经成为阻碍河湖水质达标的重要因素。选取道路、绿地和屋面3种下垫面,在武汉市开展地表径流面源污染特征研究。结果显示：降雨初期,道路下垫面COD可达115.3 mg/L,NH₃—N最高为4.12 mg/L,TP为0.55 mg/L,峰值都出现在降雨开始后的20 min。屋面径流污染物浓度与道路相似,绿地径流污染物浓度变化速率远低于道路和屋面,说明绿地对污染物浓度同样具有削峰的作用。汛期污染物浓度均值高于非汛期,是因为汛期具有小时内降雨量大的特点。南湖流域内地表径流污染高于墨水湖,主要是受建设强度和人口分布的影响。     

Thermal Pollution Mitigation in Cold Water Stream Watersheds Using Bioretention

This study examines the use of bioretention as a strategy to reduce the thermal impact associated with urban stormwater runoff in developing cold water stream watersheds. Temperature and flow data were collected during 10 controlled runs at a bioretention facility located in Blacksburg, Virginia. It was determined that bioretention has the ability to reduce the temperature of thermally charged stormwater runoff received from an asphalt surface. Significant reductions in peak and average temperatures (p < 0.001) were observed. However, this facility was unable to consistently reduce the temperature below the threshold for natural trout waters in Virginia. The ability of bioretention to reduce runoff volume and peak flow rate also serves to reduce the hydrothermal impact. An average thermal pollution reduction of nearly 37 MJ/m³ was calculated using an adopted threshold temperature of 20°C. Based on the results of this study, it was concluded that properly designed bioretention systems have the capability to reduce the thermal impact of urban stormwater runoff on cold water stream ecosystems.     

Effects of Land Use and Climate Change on Stream Temperature II: Threshold Exceedance Duration Projections for Freshwater Mussels

We developed a stochastic hourly stream temperature model (SHSTM) to estimate probability of exceeding given threshold temperature (T) for specified durations (24 and 96 h) to assess potential impacts on freshwater mussels in the upper Tar River, North Carolina. Simulated daily mean stream T from climate change (CC) and land‐use (LU) change simulations for 2021‐2030 and 2051‐2060 were used as input to the SHSTM. Stream T observations in 2010 revealed only two sites with T above 30°C for >24 h and Ts were never >31°C for more than 24 h at any site. The SHSTM suggests that the probability, P, that T will exceed 32°C for at least 96 h in a given year increased from P = 0, in the 20th Century, to P = 0.05 in 2021‐2030 and to P = 0.14 in 2051‐2060. The SHSTM indicated that CC had greater effects on P for 24 and 96 h durations than LU change. Increased P occurred primarily in higher order stream segments in the downstream reaches of the basin. The SHSTM indicated that hourly stream T responded to LU change on the daily scale and did not affect stream T for durations >24 h. The SHSTM indicated that known thermal thresholds for freshwater mussels could be exceeded within the next 50 years in many parts of the upper Tar River basin in North Carolina, which could have negative consequences on the recruitment of freshwater mussels.     

Multiscale Analysis of Hydrology in a Mountaintop Mine‐Impacted Watershed

In the Appalachian region of the eastern United States, mountaintop removal mining (MTM) is a dominant driver of land‐cover change, impacting 6.8% of the largely forested 4.86 million ha coal fields region. Recent catastrophic flooding and documented biological impairment downstream of MTM has drawn sharp criticism to this practice. Despite its extent, scale, and use since the 1970s, the impact of MTM on hydrology is poorly understood. Therefore, the goal of this study was a multiscale evaluation to establish the nature of hydrologic impacts associated with MTM. To quantify the extent of MTM, land‐cover change over the lifetime of this practice is estimated for a mesoscale watershed in southern West Virginia. To assess hydrologic impacts, we conducted long‐term trend analyses to evaluate for systematic changes in hydrology at the mesoscale, and conducted hydrometric and response time modeling to characterize storm‐scale responses of a MTM‐impacted headwater catchment. Results show a general trend in the conversion of forests to mines, and significant decreases in maximum streamflow and variability, and increases in base‐flow ratio attributed to valley fills and deep mine drainage. Decreases in variability are shown across spatial and temporal scales having important implications for water quantity and quality. However, considerable research is necessary to understand how MTM impacts hydrology. In an effort to inform future research, we identify existing knowledge gaps and limitations of our study.     

Oregon Hydrologic Landscapes: A Classification Framework1

Wigington, Parker J., Jr., Scott G. Leibowitz, Randy L. Comeleo, and Joseph L. Ebersole, 2012. Oregon Hydrologic Landscapes: A Classification Framework. Journal of the American Water Resources Association (JAWRA) 1‐20. DOI: 10.1111/jawr.12009 Abstract: There is a growing need for hydrologic classification systems that can provide a basis for broad‐scale assessments of the hydrologic functions of landscapes and watersheds and their responses to stressors such as climate change. We developed a hydrologic landscape (HL) classification approach that describes factors of climate‐watershed systems that control the hydrologic characteristics of watersheds. Our assessment units are incremental watersheds (i.e., headwater watersheds or areas draining directly into stream reaches). Major components of the classification include indices of annual climate, climate seasonality, aquifer permeability, terrain, and soil permeability. To evaluate the usefulness of our approach, we identified 30 rivers with long‐term streamflow‐gauging records and without major diversions and impoundments. We used statistical clustering to group the streams based on the shapes of their annual hydrographs. Comparison of the streamflow clusters and HL distributions within river basin clusters shows that the Oregon HL approach has the ability to provide insights about the expected hydrologic behavior of HLs and larger river basins. The Oregon HL approach has potential to be a useful framework for comparing hydrologic attributes of streams and rivers in the Pacific Northwest.     

ADEQUACY OF SELECTED EVAPOTRANSPIRATION APPROXIMATIONS FOR HYDROLOGIC SIMULATION1

ABSTRACT: Evapotranspiration (ET) approximations, usually based on computed potential ET (PET) and diverse PET‐to‐ET conceptualizations, are routinely used in hydrologic analyses. This study presents an approach to incorporate measured (actual) ET data, increasingly available using micrometeorological methods, to define the adequacy of ET approximations for hydrologic simulation. The approach is demonstrated at a site where eddy correlation‐measured ET values were available. A baseline hydrologic model incorporating measured ET values was used to evaluate the sensitivity of simulated water levels, subsurface recharge, and surface runoff to error in four ET approximations. An annually invariant pattern of mean monthly vegetation coefficients was shown to be most effective, despite the substantial year‐to‐year variation in measured vegetation coefficients. The temporal variability of available water (precipitation minus ET) at the humid, subtropical site was largely controlled by the relatively high temporal variability of precipitation, benefiting the effectiveness of coarse ET approximations, a result that is likely to prevail at other humid sites.     

EQUIVALENCE BETWEEN TOPMODEL AND THE NRCS CURVE NUMBER METHOD IN PREDICTING VARIABLE RUNOFF SOURCE AREAS1

An equivalence is proposed between two rainfall‐runoff methods with a long history of use in the United States and Europe. In watersheds where variable source areas dominate runoff, the two methods can have comparable probability distribution functions of moisture deficit, and therefore predict similar saturated runoff source areas. A novel approach is introduced to determine the S parameter in the Natural Resources Conservation Service (NRCS) method. This approach constrains S by the physical soil and topography characteristics of the catchment and depth to water table. The NRCS curve number method is at the core of many rainfall‐runoff models in hydrology. As a simple lumped parameter method, it is often scrutinized because it is not obvious how to derive S from catchment hydromorphological characteristics. The novel approach provides a clear physical meaning for S, allowing better estimation of this parameter in humid shallow water table environments where the variable source area can be the dominant runoff mechanism.     

MONTHLY RUNOFF PREDICTIONS BASED ON RAINFALL FORECASTS IN A SMALL OKLAHOMA WATERSHED1

ABSTRACT: Conditions under which monthly rainfall forecasts translate into monthly runoff predictions that could support water resources planning and management activities were investigated on a small watershed in central Oklahoma. Runoff response to rainfall forecasts was simulated using the hydrologic model SWAT. Eighteen scenarios were examined that represented combinations of wet, average, and dry antecedent rainfall conditions, with wet, normal, and dry forecasted rainfall. Results suggest that for the climatic and physiographic conditions under consideration, rainfall forecasts could offer potential application opportunities in surface water resources but only under certain conditions. Pronounced wet and dry antecedent rainfall conditions were shown to have greater impact on runoff than forecasts, particularly in the first month of a forecast period. Large forecast impacts on runoff occurred under wet antecedent conditions, when the fraction of forecasted rainfall contributing to runoff was greatest. Under dry antecedent conditions, most of the forecasted rainfall was absorbed in the soil profile, with little immediate runoff response. Persistent three‐month forecasts produced stronger impacts on runoff than one‐month forecasts due to cumulative effects in the hydrologic system. Runoff response to antecedent conditions and forecasts suggest a highly asymmetric utility function for rainfall forecasts, with greatest decision‐support potential for persistent wet forecasts under wet antecedent conditions when the forecast signal is least dampened by soil‐storage effects. Under average and dry antecedent conditions, rainfall forecasts showed little potential value for practical applications in surface water resources assessments.     

Controlling non-point-source pollution by rural resource recycling. Nitrogen runoff in Tai Lake valley, China, as an example

Agricultural non-point-source (NPS) pollution is regarded as the dominant contributor to water quality degradation and eutrophication in China. Nitrogen (N) is a primary source of pollution in fresh water bodies. In this work a linear programming model was developed to simulate the effectiveness of different nitrogen runoff control policies, using Pinghu City in Tai Lake valley as an example. Four policy scenarios were tested: a tax at a rate equivalent to 50% of the cost of nitrogen fertilizer (S1); a ban on summer fertilizer applications to make the most use of fertilizer applied in the spring (S2); mandatory substitution of regular fertilizers by controlled-release fertilizers (S3); and a subsidy of US$300 ha⁻¹ (RMB￥150 mu⁻¹) for using compost (S4). The results indicate that all four policies would effectively reduce nitrogen runoff—by 9.8, 26.8, 14.4, and 80.0%, respectively. A subsidy for recycling domestic animal manure and utilizing compost had the most significant effect on the reduction of nitrogen runoff without reducing household income. This research suggests that measures to control agricultural NPS pollution should be combined with a policy to promote recycling of bio-resources and that financial support for NPS pollution control combined with bio-resource recycling should be regarded as one aspect of public investment in regional sustainable development.     

水系分形特征对流域径流特性的影响——以赣江中上游流域为例

以赣江流域中上游的8个水文站点所控制的流域为研究对象，以水系分形维数为指标来描述流域水系特征，以Hurst指数为指标来描述流域径流序列复杂性，研究两者之间的关系，并分析流域水系特征、水系变迁对流域旱涝灾害的影响。研究表明，流域水系分维数越高，水系越复杂，其径流深序列Hurst指数则越高，其径流过程则越简单，反之亦然。径流序列的复杂程度在一定程度上可以反映出洪涝干旱灾害发生的可能性，径流越复杂，则洪涝干旱灾害发生可能性越高。因此，一般来说水系分维越高，水系越复杂，则洪涝干旱灾害发生的可能性也就越低。各流域水系分维与径流深序列的关系，可以在一定程度上说明水系变迁对洪涝干旱灾害的影响：在气温、降水、地形、植被等要素变化不大的情况下，水系、河网消亡将增加洪涝灾害和干旱灾害发生的可能性。