Evaluation of accuracy of linear regression models in predicting urban stormwater discharge characteristics

Stormwater runoff has been identified as a source of pollution for the environment, especially for receiving waters. In order to quantify and manage the impacts of stormwater runoff on the environment, predictive models and mathematical models have been developed. Predictive tools such as regression models have been widely used to predict stormwater discharge characteristics. Storm event characteristics, such as antecedent dry days （ADD）, have been related to response variables, such as pollutant loads and concentrations. However it has been a controversial issue among many studies to consider ADD as an important variable in predicting stormwater discharge characteristics. In this study, we examined the accuracy of general linear regression models in predicting discharge characteristics of roadway runoff. A total of 17 storm events were monitored in two highway segments, located in Gwangju, Korea. Data from the monitoring were used to calibrate United States Environmental Protection Agency＇s Storm Water Management Model （SWMM）. The calibrated SWMM was simulated for 55 storm events, and the results of total suspended solid （TSS） discharge loads and event mean concentrations （EMC） were extracted. From these data, linear regression models were developed. R2 and p-values of the regression of ADD for both TSS loads and EMCs were investigated. Results showed that pollutant loads were better predicted than pollutant EMC in the multiple regression models. Regression may not provide the true effect of site-specific characteristics, due to uncertainty in the data.     

Origin of major ions in monthly rainfall events at the Bamenda Highlands, North West Cameroon

Rainwater characteristics can reveal emissions from various anthropogenic and natural sources into the atmosphere. The physico-chemical characteristics of 44 monthly rainfall events （collected between January and December 2012） from 4 weather stations （Bamenda, Ndop plain, Ndawara and Kumbo） in the Bamenda Highlands （BH） were investigated. The purpose was to determine the sources of chemical species, their seasonal inputs and suitability of the rainwater for drinking. The mean pH of 5 indicated the slightly acidic nature of the rainwater. Average total dissolved solids （TDS） were low （6.7 mg/L）, characteristic of unpolluted atmospheric moisture/air. Major ion concentrations （mg/L） were low and in the order K＋ 〉 Ca2＋ 〉 Mg2~ 〉 Na＋ for cations and NO3 〉〉 HCO3 〉 SO] 〉 CI- 〉 PO3- 〉 F- for anions. The average rainwater in the area was mixed Ca-Mg-SO4-CI water type. The CI-/Na＋ ratio （1.04） was comparable to that of seawater （1.16）, an indication that N a＋ and CI originated mainly from marine （Atlantic Ocean） aerosols. High enrichments of Ca2＋, Mg2＋ and SO2- to Na＋ ratios relative to seawater ratios （constituting 44% of the total ions） demonstrated their terrigenous origin, mainly from Saharan and Sahelian arid dusts. The K＋/Na＋ ratio （2.24）, which was similar to tropical vegetation ash （2.38）, and NO3 was essentially from biomass burning. Light （〈 100 mm） pre-monsoon and post-monsoon convective rains were enriched in major ions than the heavy （〉 100 mm） monsoon rains, indicating a high contribution of major ions during the low convective showers. Despite the acidic nature, the TDS and major ion concentrations classified the rainwater as potable based on the WHO guidelines.     

山地城市典型硬化下垫面暴雨径流初期冲刷研究

为了解山地城市典型硬化下垫面暴雨径流初期冲刷效应,对山城重庆的8场暴雨进行了径流全过程监测,并与平原城市作了对比分析.结果表明:TSS(总悬浮物)、COD和TP来自城市交通干道的贡献较混凝土屋面大,而TN、NH3-N两者相当;对于重金属,除Cd外,城市交通干道重金属的EMC(Event Mean Concentration)值均高于混凝土屋面.城市交通干道,初期40%的暴雨径流携带了53%±16%TSS,66%±10%COD,59%±2%TN,58%±2%NH3-N,51%±5%TP;而混凝土屋面,初期40%的暴雨径流携带了64%±20%TSS,66%±17%COD,55%±14%TN,52%±14%NH3-N,56%±3%TP,建议两类硬化下垫面至少以初期40%的暴雨径流作为控制量.与平原城市相比,山地城市交通干道初期40%的暴雨径流携带污染负荷TSS与COD的比例比平原城市分别高出16%和22%,初期冲刷效应更加明显.     

半干旱半湿润地区HSPF模型水文模拟及参数不确定性研究

本研究选取半干旱半湿润地区北京妫水河流域2005—2007年和2008年月径流数据为率定期和验证期,建立HSPF水文模型进行径流模拟,结合人工率定和PEST自动率定程序进行参数优选,并通过GLUE方法分析模型参数不确定性.通过Monte-Carlo随机采样得到30000组参数组合,分析参数与似然值散点图,把参数分为敏感参数(LZSN、AGWRC)、区间敏感参数(BASETP)和不敏感参数(AGWETP、INFILT、CEPSC、DEEPFR、UZSN、INTFW、IRC).针对比较敏感的参数LZSN、AGWRC和BASETP分析其相关性,发现LZSN和AGWRC相关性较强.模型存在大量"异参同效"现象,表明影响结果的是参数组合而不是单一参数.进一步计算90%置信度下的不确定性范围,发现不确定性范围与径流大小密切相关,径流愈大其不确定性范围愈大,反之亦然.本文对参数不确定的分析研究可为HSPF模型在区域尺度水文预测等提供参考和依据.     

降雨和土地利用对地表径流的影响-以北京北护城河周边区域为例

以北京北护城河周边区域为例,探讨了降雨和土地利用对地表径流的影响。选取了2011-2012 年4-11 月的15 场降雨,分别代表小雨、中雨、大雨、暴雨、大暴雨和特大暴雨这6 个雨量级。利用校准的雨洪管理模型（Storm Water Management Model, SWMM）分别模拟每次降雨事件下研究区7 个控制断面的地表径流深度。结果表明,地表径流深度随降雨量的增加显著线性增加。当降雨量在不同量级之间变化时,地表径流深度的变化幅度不尽相同。在不同的降雨事件中,降雨量和地表径流深度随时间的动态变化趋势可能有很大的差异,但地表径流深度在某一时刻的值的高低均决定于之前1~2 h 的降雨量,而地表径流深度的总体上升或下降趋势均决定于前期累积的降雨量。地表径流深度随渗透面积比例的增加显著下降,且变化曲线存在临界阈值（为15%~20%）。在暴雨、大暴雨和特大暴雨时,渗透面积比例对地表径流的影响更大。研究结果可为控制汛期城市地表径流量和洪峰流量、减少城市内涝提供土地利用和管理方面的理论依据和决策建议。     

3种生物滞留设计对城市地表径流溶解性氮的去除作用

城市地表径流溶解性氮(N)的有效控制具有挑战性.2015构建了3种不同设计的生物滞留设施:壤砂种植紫穗狼尾草(CB)、壤砂种植紫穗狼尾草设置饱和带(MB1)、壤砂种植紫穗狼尾草设置饱和带并添加10%木块(MB2).在模拟城市地表径流水文、水质变化条件下,研究3种生物滞留种植植物、设置饱和带以及添加碳源对城市地表径流溶解性N(NH_4~+-N、NO_3~--N)的去除作用.通过为期1年试验监测表明,在进水NH_4~+-N浓度平均值为(5.45±2.21)mg·L-1情况下,3种生物滞留对NH_4~+-N均具有显著的去除作用(去除率95%).基质吸附、硝化与植物吸收是生物滞留有效去除城市地表径流NH_4~+-N的主要途径.在进水NO_3~--N平均值为(5.88±2.32)mg·L-1情况下,CB、MB1和MB2出水NO_3~--N浓度的平均值分别为(4.04±2.64)、(0.84±1.18)和(0.26±0.48)mg·L-1,相应去除率分别为31.3%、85.7%和95.6%.生物滞留种植紫穗狼尾草、设置饱和带以及添加碳源均可显著降低出水NO_3~--N浓度,减少NO_3~--N淋溶输出,提高NO_3~--N去除率.植物吸收和微生物反硝化是生物滞留去除NO_3~--N的主要途径.进水NO_3~--N浓度、水量、间隔天数是影响生物滞留出水NO_3~--N浓度的主要因素.生物滞留种植紫穗狼尾草、设置饱和带并添加碳源,在水文、水质变化情况下,仍可有效去除城市地表径流溶解性N.     

太湖上游城市宜兴城区主干道路径流污染特征解析

通过监测2015年8月—2016年9月7场典型降雨事件,系统分析太湖上游城市宜兴城区3个不同功能区(环科园、新城区和老城区)主干道路径流污染特征.研究表明:宜兴市城区主干道路径流浊度、COD、TN、NH_3-N、TP浓度分别为(77.2±66.9)NTU、(97.2±79.7)、(3.0±1.9)、(0.93±0.59)和(0.35±0.36)mg·L~(-1).COD和TN超出地表水环境Ⅴ类标准,是该地区径流特征污染物.降雨过程中污染物浓度整体呈下降趋势,伴随有不同程度的波动,主要受地表残留污染物及降雨强度的影响.3个区域TN浓度差异不大,且主要以溶解态存在(60%);环科园、新城区TP浓度差异不大,且主要以颗粒态存在(70%);然而,受居民生活活动的影响,老城区TP主要以溶解态存在(60%).此外,受交通及道路坡度影响,新城区道路径流浊度和COD污染最为严重.不同降雨事件径流污染物浓度变化较大,主要受干期长度和降雨强度的影响.干期长度越长、降雨强度越小,污染物累积量及可冲刷量越大.因此,加强控制宜兴市道路初期径流、路面颗粒物、径流颗粒物和TN以及老城区TP,对保护径流主要受纳水体南溪水系及太湖水体具有重要意义.     

Spectroscopic Distribution of Dissolved Organic Matter in a Dam Reservoir Impacted by Turbid Storm Runoff

Spectroscopic characteristics of dissolved organic matter (DOM) in a large dam reservoir were determined using ultraviolet absorbance and fluorescence spectroscopy to investigate spatial distribution of DOM composition after turbid storm runoff. Water samples were collected along a longitudinal axis of the reservoir at three to four depths after a severe storm runoff. Vertical profiles of turbidity data showed that a turbid water layer was located at a middle depth of the entire reservoir. The spectroscopic characteristics of DOM samples in the turbid water layer were similar to those of terrestrial DOM, as demonstrated by the higher specific UV absorbance (SUVA) and the lower fluorescence emission intensity ratio (F ₄₅₀/F ₅₀₀) compared to other surrounding DOM samples in the reservoir. Synchronous fluorescence spectroscopy revealed that higher content of humic-like DOM composition was contained in the turbid water. Fluorescence excitation–emission matrix (EEM) showed that lower content of protein-like aromatic amino acids was present in the turbid water DOM. The highest protein-like fluorescence was typically observed at a bottom layer of each sampling location. The bottom water DOM exhibited extremely high protein-like florescence near the dam site. The particular observation was attributed to the low water temperature and the isolation of the local bottom water due to the upper location of the withdrawal outlet near the dam. Our results suggest that the distribution of DOM composition in a dam reservoir is strongly influenced by the outflow operation, such as selective withdrawal, as well as terrestrial-origin DOM inputs from storm runoff.     

An Analysis of Patterns and Trends in United States Stormwater Utility Systems

Several factors, such as municipality location and population, are thought to influence trends among stormwater utilities (SWUs); however, no analysis of the relationship between these factors and SWU characteristics has been performed. This article corroborates hypothesized relationships and identifies trends and patterns in the establishment, funding mechanism, and magnitude of SWUs by analyzing location, population density, home value, and year of establishment for a comprehensive national SWU database with data for 1,490 SWUs. The equivalent residential unit (ERU), a SWU that charges based on impervious area, was the most prevalent funding mechanism in all National Oceanic and Atmospheric Administration Climate Regions of the United States except the West and West‐North‐Central. The ERU was also found in larger cities with high population densities, whereas the Flat Fee, a SWU that charges a single rate for all properties, was found in smaller towns. Higher home values were correlated with higher monthly fees for 28% of the municipalities analyzed. The residential equivalence factor, a SWU that charges based on runoff produced, was popular in municipalities with higher home values, whereas the Flat Fee was popular in municipalities with lower home values. The number of SWUs established increased with Phase I municipal separate stormwater and sewer system (MS4) permit and Phase II small MS4 permit deadlines. Summary tables provide guidance to aid municipalities considering a SWU.     

Impacts of Changes in Precipitation Amount and Distribution on Water Resources Studied Using a Model Rainwater Harvesting System

Water supply reliability is expected to be affected by both precipitation amount and distribution changes under recent and future climate change. We compare historical (1951‐2010) changes in annual‐mean and annual‐maximum daily precipitation in the global set of station observations from Global Historical Climatology Network and climate models from the Inter‐Sectoral Impact Model Intercomparison Project (ISI‐MIP), and develop the study to 2011‐2099 for model projections under high radiative forcing scenario (RCP8.5). We develop a simple rainwater harvesting system (RWHS) model and drive it with observational and modeled precipitation. We study the changes in mean and maximum precipitation along with changes in the reliability of the model RWHS as tools to assess the impact of changes in precipitation amount and distribution on reliability of precipitation‐fed water supplies. Results show faster increase in observed maximum precipitation (10.14% per K global warming) than mean precipitation (7.64% per K), and increased reliability of the model RWHS driven by observed precipitation by an average of 0.2% per decade. The ISI‐MIP models show even faster increase in maximum precipitation compared to mean precipitation. However, they imply decreases in mean reliability, for an average 0.15% per decade. Compared to observations, climate models underestimate the increasing trends in mean and maximum precipitation and show the opposite direction of change in reliability of a model water supply system.