Stormwater Network Research Articles

Investigating the Response of a Small Urbanized Watershed to Acute Toxicity Events via Analysis of High-frequency Environmental Data

This study, conducted over 10 weeks by an undergraduate student in an NSF REU (U.S. National Science Foundation Research Experiences for Undergraduates) program under mentorship of the co-authors, investigates responses of a small urban watershed, located in Blacksburg, Virginia, to acute toxicity events. High-frequency water and weather data were collected using monitoring equipment maintained by the Learning Enhanced Watershed Assessment System (LEWAS) lab, including a weather station, rain gauge, water quality sonde, and an Acoustic Doppler Current Profiler. The location and attributes of local stormwater catchments were surveyed and recorded using GIS software to determine the overall contributing area of the LEWAS lab watershed. This fieldwork resulted in the construction of an accurate stormwater network map, which in turn allowed the identification of sources of sedimentation and other pollution from runoff events. A case study presents the response of the watershed to a winter storm event that resulted in acute chloride toxicity from runoff containing road salts. KEYWORDS: Water; Stormwater, Urban Watersheds; Watershed Responses; Acute Toxicity; High-frequency Data; Data Analysis; Data Collection; Environmental Monitoring; Flow Measurements; Hydrologic Data.

Green-roof as a solution to solve stormwater management issues? Assessment on a long time period at the parcel scale

Abstract. Experimental green-roof rainfall–runoff observations have shown a positive impact on stormwater management at the building scale; with a decrease in the peak discharge and a decrease in runoff volume. This efficiency of green-roofs varies from one rainfall event to another depending on precipitation characteristics and substrate antecedent conditions. Due to this variability, currently, green-roofs are rarely officially used as a regulation tool to manage stormwater. Indeed, regulation rules governing the connection to the stormwater network are usually based on absolute threshold values that always have to be respected: maximum areal flow-rate or minimum retention volume for example. In this context, the aim of this study is to illustrate how a green-roof could represent an alternative to solve stormwater management issues, if the regulation rules were further based on statistics. For this purpose, a modelling scheme has been established at the parcel scale to simulate the hydrological response of several roof configurations: impervious, strictly regulated (in terms of areal flow-rate or retention volume), and covered by different types of green-roof matter. Simulations were carried out on a long precipitation time period (23 years) that included a large and heterogeneous set of hydrometeorological conditions. Results obtained for the different roof configurations were compared. Based on the return period of the rainfall event, the probability to respect some regulation rules (defined from real situations) was assessed. They illustrate that green-roofs reduce stormwater runoff compared to an impervious roof surface and can guarantee the respect of the regulation rules in most of the cases. Moreover, their implementation can appear more realistic than that of other infrastructures strictly complying with regulations and demanding significant storage capacity.

Nutrient Enrichment and Proliferation of Invasive Macrophytes in Urban Lakes

(CA) ABSTRACT Sewage generated in urban households is either untreated or partially treated, which finally let into water bodies through storm water network. Sustained inflow of sewage into water bodies though maintained the water levels in the system of interconnected lakes has contributed to the nutrient enrichment of surface as well as groundwater sources. Nutrient enrichment in urban water bodies has become one of the major environmental concerns in rapidly urbanizing towns and cities in India. In this context, the current study carries out comparative analysis of water quality and ecological health of twelve urban wetlands in Bangalore. Principal component analysis (PCA) and Cluster analysis (CA) were done to assess the ecological integrity of wetlands based on the data of 15 physico-chemical parameters. The loadings of the first and second principal components explain the pollution. CA grouped the wetlands into four distinct clusters: less polluted, moderately polluted, highly polluted and severely polluted based on the water quality parameters. This analyses brings out the importance of regular monitoring and the need to restore and sustainable management of wetlands. The sustained inflow of untreated and partially treated sewage, urban runoff, etc. are the drivers of wetlands quality deterioration.

Modeling Sewer Overflow of a City with a Large Floating Population

The sewer system of many historical or holy cities is not well associated with the present need. The managing of the sewer system of such cities is very difficult. Karbala, located in central Iraq, is one such city that experiences tremendous pressure on its sewer system due to large visiting population during special religious gathering. As the sewer system of Karbala city is not designed for such high population like many other historic or holy cities, the sewer overflows, inundate the roads, and degrade the environmental due to the polluted sewer during religious gatherings. The problem often becomes critical due to heavy rainfall as the gathering usually happens during monsoon. The modeling of the sewer water quantity with a varying population and rainfall is important for simulating the sewer overflow as well as to manage the sewer system. The modeling of the sewer water quality is also important to understand the possible environmental hazard due to the sewer overflow. In this present study, an attempt has been taken to simulate the spatiotemporal distribution of the sewer water quantity and quality with a varying population and rainfall for the prediction of sewer overflow and possible pollution susceptibility. The Stormwater Management Model (SWMM) will be used in the proposed study. The simulation will be carried out in the city center of the Karbala city where the stormwater network is not fully developed. It is expected that this study will help in the operational management of the sewerage system and mitigate the sewer flooding and related environmental problems.

Stormwater quality improvement potential of an urbanised catchment using water sensitive retrofits into public parks

Urban stormwater management is undergoing a transition from centralised hydrologically efficient systems to collections of dispersed, multi-functional elements. In response to a better understanding of impervious surface areas, the adoption of water sensitive urban design is promising for new large urban developments. However, spatial and economic constraints prohibit its adoption in established urban areas. We explore the potential for improvement to stormwater quality if 10% of existing parks in an established urban catchment are reserved for stormwater filtration. Spatially explicit hydrologic modelling is used to model the effects of parks in an existing urban catchment in South Australia as networks of bioretention devices. The allocation of 10% of parks that cover less than 16% of the landscape for bioretention devices may result in a 62% reduction (7.8 tonnes per year) of nitrogen from stormwater. The sources and destinations of stormwater pollutants are mapped to explore the strength and weaknesses of park size and distribution within each sub-catchment. Large parks situated lower in the catchment along the main trunk, and distributed smaller parks higher along the secondary stormwater network are shown to be effectively located. The potential for increasing the utilitarian value of many public parks by demonstrating the capacity for significantly improving urban stormwater quality is illustrated in this exploratory model. Opportunities for targeted improvements to stormwater quality are examined in the discussion.

Using biofilm as a novel approach to assess stormwater treatment efficacy

Contaminants associated with stormwater are among the leading causes of water quality impairment in urban streams. Multiple device treatment systems are commonly installed with the aim of reducing contaminant loads within stormwater discharge. However, the in situ performance of such systems remains poorly understood. We investigated the efficacy of an advanced stormwater treatment system by monitoring biofilm associated metals and biofilm bacterial community composition at multiple locations through the treatment system (which included rain gardens, grassy swales, a stormwater filter and a wetland) and in the receiving stream above and below the stormwater discharge. Changes in bacterial community composition were assessed by Automated Ribosomal Intergenic Spacer Analysis (ARISA) and concentrations of biofilm associated metals monitored by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Significant differences in bacterial community composition were detected throughout the stormwater network. Bacterial communities gradually changed towards a community more similar to that within the receiving stream and the discharge of treated stormwater had little effect on the composition of bacterial communities in the receiving stream, suggesting the effective conditioning of water quality by the treatment system. Concentrations of some biofilm-associated metals declined following sequential treatment, for example copper (73% reduction), zinc (48% reduction) and lead (46% reduction). In contrast, levels of arsenic, cadmium, chromium and nickel were not reduced by the treatment system. We demonstrate that biofilm bacterial community composition is a sensitive indicator of environmental changes within freshwater ecosystems and an efficient indicator to monitor water quality in enclosed stormwater networks where traditional biological indicators are not available.

Treatment experiments for removal of hydrogen sulfide from saline groundwater in Kuwait

Laboratory and field experiments have been carried out to find an optimum method for the treatment of hydrogen sulfide-rich groundwater that often occurs at comparatively shallow depths (15–40 m from the surface) in the urban areas of Kuwait City and is pumped to the surface during dewatering of the construction sites. The treatment would be necessary to remove the gas from the pumped groundwater before its disposal, either on the surface or to the stormwater network, to avoid health and environmental hazards created by the release of the hydrogen sulfide gas, which is toxic, to the atmosphere or to the sea. Based on these experiments, it has been recommended that an economic and reliable hydrogen sulfide treatment facility for groundwater pumped at the study area should consist of sand filters, followed by aeration units for the removal of major part (60–70%) of hydrogen sulfide. Chlorination or activated carbon adsorption can be utilized as a polishing process to remove the residual hydrogen sulfide, depending on its concentration in the water after the aeration treatment and the rate of groundwater pumping.

Prediction of water and wastewater networks rehabilitation based current age and material distribution

Ageing drinking water, stormwater and sewer pipe networks imply an increased degree of rehabilitation. The need for rehabilitation can be predicted using lifetime distribution functions together with current network age and material distribution. In Sweden, current age and material distribution is neither documented on a national level, nor for many water utilities on a local level. In this study, current network age and material distribution was provided through a questionnaire sent to Swedish water and wastewater utilities and the data provided were extrapolated to cover the whole of Sweden. The data were then combined with lifetime distribution functions to provide predictions. One limitation is that for newer materials the lifetime is still uncertain. Predictions were made for different scenarios to reflect local differences and the medium scenario shows that while the Swedish rehabilitation rate is stable, investments in monetary terms need to double in the next 60 years. The rehabilitation rate is also dependent on the extent to which the network is expanded. This method can be used to calculate national investment needs, and the results can also provide a basis for estimates for Swedish utilities with data scarcity.

Rebirthing genetic algorithm for storm sewer network design

Application of standard binary coded genetic algorithms for the solution of problems with continuous design variables requires discretization of the continuous decision variables. Coarse discretization of the design variables could adversely affect the final solution, while finer discretization would increasingly enlarge the scale of the problem, leading to higher computation cost. A rebirthing procedure is used in this paper as a remedy for the problem just outlined. The method is based on the idea of limiting the originally wide search space to a smaller one once a locally converged solution is obtained. The smaller search space is designed to contain the locally optimum solution at its center. The resulting search space is refined and a completely new search is conducted to find a better solution. The procedure is continued until no refinement is necessary or no improvement could be made by further refinement. The method is applied to a benchmark problem of a storm water network design, and the results are compared with those of the existing method. The method is shown to be very effective, efficient and insensitive to the population size of the genetic search and the search space size of the optimization problem.

Pollutant concentrations and fluxes in both stormwater and wastewater at the outlet of two urban watersheds in Nantes (France)

A two-year study of pollutants in both the stormwater and wastewater of urban watersheds has been conducted in Nantes (France). The present paper discusses the characteristics of pollutants transported by stormwater and wastewater collection networks in two urban watersheds. A physicochemical characterisation of the effluents was performed, along with an estimation of pollutant fluxes discharged into the Gohards River. Suspended solids (SS), trace metals, polycyclic aromatic hydrocarbons (PAHs) and pesticides were studied. SS, Zn, Cu and glyphosate were the main pollutants in stormwater and wastewater. In the watersheds examined, the pyrolitic origin of PAHs (mainly from traffic) was determined through ratios, with fluoranthene and pyrene being predominant. Despite a reduction in the use of pesticides in Nantes Metropolitan area, herbicides containing glyphosate were still detected in stormwater. It should be noted that this herbicide is widely used by homeowners, a fact that may explain its occurrence in stormwater.

Underdrain Configuration to Enhance Bioretention Exfiltration to Reduce Pollutant Loads

The bioretention drainage configuration of raising the outlet to create an internal water storage (IWS) layer in the media was originally intended to promote denitrifying conditions. The goal was to reduce nitrate and total nitrogen concentrations in nutrient-sensitive watersheds. Two field studies in the Piedmont region of North Carolina, where the in situ soils typically have high clay content, showed this design feature had potential to enhance exfiltration and reduce drainage from bioretention. Two bioretention cells in Rocky Mount, North Carolina, were monitored for two year-long periods to measure the impact of varying IWS zone depths over sandier underlying soils. Nearly 99% of runoff entering the bioretention cell with sand underlying soil (sand cell) was never directly discharged to the storm water network. However, the hydraulic retention time (contact time) of runoff in the media was less than 3 h, and except for total suspended solids (TSS), minimal pollutant removal was achieved. The other bi...

Bioretention Hydrologic Performance in an Urban Stormwater Network

Although many studies have evaluated the hydrologic effects of bioretention at the site-level, few have investigated the role bioretention plays when distributed throughout a watershed. This study aims to assess bioretention’s effects on an urbanized watershed in Blacksburg, Virginia by using two modeled scenarios: one where runoff from many land uses was routed through the practice, and another in which only runoff from large impervious areas was routed. Peak flows, volumes, and lag times from these models were compared to the watershed’s current and predeveloped conditions. Both scenarios provided reductions in peak flows with respect to existing conditions for modeled storm events, sometimes to levels below the predeveloped condition. Neither case was able to reduce volumes to predevelopment levels; the option to treat impervious areas had a negligible effect on runoff volume. Both cases were able to extend lag times from the existing development condition. On the basis of these results, bioretention a...

Impact of carwash discharge on stormwater quality (Toulouse, France)

The contribution of discharge from carwashes to pollutant levels in stormwater was evaluated. Five carwashes and two outlets in the city of Toulouse (France) were selected. Water samples were collected from December 2006 to December 2007. Concentrations and loadings of classical water quality parameters (conductivity, pH, turbidity, chemical oxygen demand, nitrogen, phosphorus, ammonium, nitrate, suspended solid and volatile suspended solid) and five groups of organic compounds (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, lauryl alkyl benzene sulphonates, methyl tert-butyl ether and total hydrocarbons) were determined. The results suggest that the wastewater derived from carwashes was negligible compared to the volume and flow rates within the stormwater network. However, high concentrations of polycyclic aromatic hydrocarbons, phosphorus and lauryl alkyl benzene sulphonates in liquid waste from carwashes, and the impact of these pollutants on stormwater quality could not be neglected.

Locating illicit connections in storm water sewers using fiber-optic distributed temperature sensing

A newly developed technique using distributed temperature sensing (DTS) has been developed to find illicit household sewage connections to storm water systems in the Netherlands. DTS allows for the accurate measurement of temperature along a fiber-optic cable, with high spatial (2 m) and temporal (30 s) resolution. We inserted a fiber-optic cable of 1300 m in two storm water drains. At certain locations, significant temperature differences with an intermittent character were measured, indicating inflow of water that was not storm water. In all cases, we found that foul water from households or companies entered the storm water system through an illicit sewage connection. The method of using temperature differences for illicit connection detection in storm water networks is discussed. The technique of using fiber-optic cables for distributed temperature sensing is explained in detail. The DTS method is a reliable, inexpensive and practically feasible method to detect illicit connections to storm water systems, which does not require access to private property.

Rebirthing particle swarm optimization algorithm: application to storm water network design

Stochastic search methods, such as the particle swarm optimization (PSO) algorithm, are primarily directed by two main features — exploration and exploitation. Exploration is the ability of the algorithm to broadly search through the solution space for new quality solutions, whereas exploitation is responsible for refining the search in the neighborhood of the good solutions found previously. Proper balance between these features is sought, to obtain good performance of these algorithms. An explorative mechanism is introduced in this paper to improve the performance of the PSO algorithm. The method is based on introducing artificial exploration into the algorithm by randomly repositioning the particles approaching stationary status. A velocity measure is used to distinguish between flying and stationary particles. This can be sought as a sudden death followed by a rebirth of these particles. Two options are tested for the rebirthing mechanism, which are (i) clearing and (ii) keeping the memory of rebirthing particles. The global best particle is exempted from rebirthing process so that the most useful of the swarm’s past experiences is not lost. The method is applied to a benchmark storm water network design problem and the results are presented and compared with those of the original algorithm and other methods. The proposed method, though simple, is shown to be very effective in avoiding local optima, leading to an improved version of the algorithm at no extra computational effort.

Partially constrained ant colony optimization algorithm for the solution of constrained optimization problems: Application to storm water network design

This paper exploits the unique feature of the Ant Colony Optimization Algorithm (ACOA), namely incremental solution building mechanism, to develop partially constraint ACO algorithms for the solution of optimization problems with explicit constraints. The method is based on the provision of a tabu list for each ant at each decision point of the problem so that some constraints of the problem are satisfied. The application of the method to the problem of storm water network design is formulated and presented. The network nodes are considered as the decision points and the nodal elevations of the network are used as the decision variables of the optimization problem. Two partially constrained ACO algorithms are formulated and applied to a benchmark example of storm water network design and the results are compared with those of the original unconstrained algorithm and existing methods. In the first algorithm the positive slope constraints are satisfied explicitly and the rest are satisfied by using the penalty method while in the second one the satisfaction of constraints regarding the maximum ratio of flow depth to the diameter are also achieved explicitly via the tabu list. The method is shown to be very effective and efficient in locating the optimal solutions and in terms of the convergence characteristics of the resulting ACO algorithms. The proposed algorithms are also shown to be relatively insensitive to the initial colony used compared to the original algorithm. Furthermore, the method proves itself capable of finding an optimal or near-optimal solution, independent of the discretisation level and the size of the colony used.

Optimization of Frequency Distribution of Storm-Water Discharges for Coastal Ecosystem Restoration

Many coastal ecosystems have been adversely impacted by increased storm-water drainage due to expanding urbanization. The ecosystem of the St. Lucie Estuary SLE, located on the east coast of south Florida, has been greatly influenced by development of an intricate network of storm-water drainage canals in the tributary watershed. A suite of models dealing with watershed hydrology, reservoir optimization, and estuary salinity and ecology are applied for optimal sizing and operation of storm-water reservoirs. The multipurpose storm-water control facilities provide for hydrologic restoration to predrained or natural hydrologic conditions for recovery of salinity- sensitive biota in the SLE, as well as supplemental irrigation water and pollution control through connected storm-water treatment areas. The optimization is challenging since the ecological goal is for mean monthly storm-water discharges to the SLE to coincide with the desired natural frequency distribution, rather than simply attempting to control individual extreme events. The OPTI6 optimization model applies a genetic algorithm, coupled with a daily simulation model of the storm-water drainage network, to optimize the sizing and fuzzy operating rules of reservoirs for controlling storm-water discharges to the SLE. Results indicate that the desired frequency distribution is closely matched and the level of service for the supplemental irrigation demand is met under reduced storage requirements.

Hydrograph-based storm sewer design optimization by genetic algorithm

A model is developed for the optimal design of storm water networks. The model uses a genetic algorithm (GA) as the search engine and the TRANSPORT module of the US Environmental Protection Agency storm water management model version 4.4H (SWMM4.4H) as the hydraulic simulator. Two different schemes are used to formulate the problem with varying degrees of success in reaching a near-optimal solution. In the first scheme, the nodal elevations and pipe diameters are selected as the decision variables of the problem which were determined by the GA to produce the trial solutions. In the second scheme, only nodal elevations are optimized by the GA, and determination of pipe diameters is left to the TRANSPORT SWMM module. Simulation of the trial solutions in both methods is carried out by the TRANSPORT module of SWMM4.4H. The proposed model is applied to some benchmark examples, and the results are presented and compared with the existing results in the literature.Key words: genetic algorithm, optimal design, sewer network, SWMM.

Improving the efficiency of ant algorithms using adaptive refinement: Application to storm water network design

The ant algorithm is a new evolutionary optimization method proposed for the solution of discrete combinatorial optimization problems. Many engineering optimization problems involve decision variables of continuous nature. Application of the ant algorithm to the optimization of these continuous problems requires discretization of the continuous search space, thereby reducing the underlying continuous problem to a discrete optimization problem. The level of discretization of the continuous search space, however, could present some problems. Generally, coarse discretization of the continuous design variables could adversely affect the quality of the final solution while finer discretization would enlarge the scale of the problem leading to higher computation cost and, occasionally, to low quality solutions. An adaptive refinement procedure is introduced in this paper as a remedy for the problem just outlined. The method is based on the idea of limiting the originally wide search space to a smaller one once a locally converged solution is obtained. The smaller search space is designed to contain the locally optimum solution at its center. The resulting search space is discretized and a completely new search is conducted to find a better solution. The procedure is continued until no improvement can be made by further refinement. The method is applied to a benchmark problem in storm water network design discipline and the results are compared with those of existing methods. The method is shown to be very effective and efficient regarding the optimality of the solution, and the convergence characteristics of the resulting ant algorithm. Furthermore, the method proves itself capable of finding an optimal, or near-optimal solution, independent of the discretization level and the size of the colony used.

The hydraulic capacity of deteriorating sewer systems

Sewer and wastewater systems suffer from insufficient capacity, construction flaws and pipe deterioration. Consequences are structural failures, local floods, surface erosion and pollution of receiving waters bodies. European cities spend in the order of five billion Euro per year for wastewater network rehabilitation. This amount is estimated to increase due to network ageing. The project CARE-S (Computer Aided RE-habilitation of Sewer Networks) deals with sewer and storm water networks. The final project goal is to develop integrated software, which provides the most cost-efficient system of maintenance, repair and rehabilitation of sewer networks. Decisions on investments in rehabilitation often have to be made with uncertain information about the structural condition and the hydraulic performance of a sewer system. Because of this, decision-making involves considerable risks. This paper presents the results of research focused on the study of hydraulic effects caused by failures due to temporal decline of sewer systems. Hydraulic simulations are usually carried out by running commercial models that apply, as input, default values of parameters that strongly influence results. Using CCTV inspections information as dataset to catalogue principal types of failures affecting pipes, a 3D model was used to evaluate their hydraulic consequences. The translation of failures effects in parameters values producing the same hydraulic conditions caused by failures was carried out through the comparison of laboratory experiences and 3D simulations results. Those parameters could be the input of 1D commercial models instead of the default values commonly inserted.