Juan Pablo Rodríguez

A database and model to support proactive management of sediment-related sewer blockages.

Due to increasing customer and political pressures, and more stringent environmental regulations, sediment and other blockage issues are now a high priority when assessing sewer system operational performance. Blockages caused by sediment deposits reduce sewer system reliability and demand remedial action at considerable operational cost. Consequently, procedures are required for identifying which parts of the sewer system are in most need of proactive removal of sediments. This paper presents an exceptionally long (7.5 years) and spatially detailed (9658 grid squares--0.03 km² each--covering a population of nearly 7.5 million) data set obtained from a customer complaints database in Bogotá (Colombia). The sediment-related blockage data are modelled using homogeneous and non-homogeneous Poisson process models. In most of the analysed areas the inter-arrival time between blockages can be represented by the homogeneous process, but there are a considerable number of areas (up to 34%) for which there is strong evidence of non-stationarity. In most of these cases, the mean blockage rate increases over time, signifying a continual deterioration of the system despite repairs, this being particularly marked for pipe and gully pot related blockages. The physical properties of the system (mean pipe slope, diameter and pipe length) have a clear but weak influence on observed blockage rates. The Bogotá case study illustrates the potential value of customer complaints databases and formal analysis frameworks for proactive sewerage maintenance scheduling in large cities.

Sediment and pollutant load modelling using an integrated urban drainage modelling toolbox: an application of City Drain

Numerical and computational modelling of flow and pollutant dynamics in urban drainage systems is becoming more and more integral to planning and design. The main aim of integrated flow and pollutant models is to quantify the efficiency of different measures at reducing the amount of pollutants discharged into receiving water bodies and minimise the consequent negative water quality impact. The open source toolbox CITY DRAIN developed in the Matlab/Simulink environment, which was designed for integrated modelling of urban drainage systems, is used in this work. The goal in this study was to implement and test computational routines for representing sediment and pollutant loads in order to evaluate catchment surface pollution. Tested models estimate the accumulation, erosion and transport of pollutants--aggregately--on urban surfaces and in sewers. The toolbox now includes mathematical formulations for accumulation of pollutants during dry weather period and their wash-off during rainfall events. The experimental data acquired in a previous research project carried out by the Environmental Engineering Research Centre (CIIA) at the Universidad de los Andes in Bogotá (Colombia) was used for the calibration of the models. Different numerical approaches were tested for their ability to calibrate to the sediment transport conditions. Initial results indicate, when there is more than one peak during the rainfall event duration, wash-off processes probably can be better represented using a model based on the flow instead of the rainfall intensity. Additionally, it was observed that using more detailed models (compared with an instantaneous approach) for representing pollutant accumulation do not necessarily lead to better results.

Monitoring and modelling to support wastewater system management in developing mega-cities.

Urban drainage system models can be useful to assess and manage system performance and to plan its development. However, due to data and computational costs, sophisticated, high-resolution contemporary models of the sewer system may not be applicable. This constraint is particularly marked in developing country mega-cities where catchments can be large, data tend to be scarce, and there are many unknowns, for example regarding sources, losses and wrong connections. This paper presents work undertaken over the last 7 years to develop a suitable monitoring and modelling framework to support operation and development of the wastewater system of Bogotá (Colombia). Components of the framework covered here are: (a) the flow and water quality database, (b) a wastewater pollution load generator, and (c) a semi-distributed sewer network model, which aims at a complexity that matches the information available from the previous two components. Results from a catchment within Bogotá, area 150 km(2) and with 2.5 million inhabitants, show that the model outputs capture the scale and dynamics of the observed concentrations and loads at various points on the sewer system. However uncertainty is high because much of variability of observed dry weather flow profiles is apparently random. Against this variability, the effects of in-sewer processes were not identifiable except where backwaters caused particularly high retention times. Hence the work has resulted in an operational model with a scientifically justified, yet useful, level of complexity for Bogotá. More generally, the work demonstrates the value of monitoring and modelling programmes, including having modellers actively involved in monitoring specification and operations; and the insights into suitable level of model complexity that may be gained by uncertainty and sensitivity analysis.

Generating time-series of dry weather loads to sewers

Availability of appropriate methods for quantifying temporal and spatial variations of inflows to sewer systems is a prerequisite to effective sewer system modelling. To contribute to this goal, an empirical generator of sub-catchment wastewater outputs, for use as flow and water quality inputs to dynamic simulations of the larger sewerage system, is developed and evaluated. The deterministic part of the model is represented by means of Fourier series to generate diurnal profiles and a linear regression to generalise between sites, while a novel application of a multivariate error model with a lag-one autoregression term provides a stochastic component. Using a case study of Bogota (Colombia), the validities of model assumptions are analysed and model results are compared with available dry weather measurements. The transferability of the methodology to other drainage systems is partially assessed using Linz (Austria) as a case study. It is concluded that the stochastic generator is a useful tool for generating flow and water quality at gauged and ungauged sub-catchment outlets in Bogota and potentially other catchments.

Impact of rainfall temporal resolution on urban water quality modelling performance and uncertainties

A key control on the response of an urban drainage model is how well the observed rainfall records represent the real rainfall variability. Particularly in urban catchments with fast response flow regimes, the selection of temporal resolution in rainfall data collection is critical. Furthermore, the impact of the rainfall variability on the model response is amplified for water quality estimates, as uncertainty in rainfall intensity affects both the rainfall-runoff and pollutant wash-off sub-models, thus compounding uncertainties. A modelling study was designed to investigate the impact of altering rainfall temporal resolution on the magnitude and behaviour of uncertainties associated with the hydrological modelling compared with water quality modelling. The case study was an 85-ha combined sewer sub-catchment in Bogotá (Colombia). Water quality estimates showed greater sensitivity to the inter-event variability in rainfall hyetograph characteristics than to changes in the rainfall input temporal resolution. Overall, uncertainties from the water quality model were two- to five-fold those of the hydrological model. However, owing to the intrinsic scarcity of observations in urban water quality modelling, total model output uncertainties, especially from the water quality model, were too large to make recommendations for particular model structures or parameter values with respect to rainfall temporal resolution.

On the preventive management of sediment-related sewer blockages: a combined maintenance and routing optimization approach

In this work we tackle the problem of planning and scheduling preventive maintenance (PM) of sediment-related sewer blockages in a set of geographically distributed sites that are subject to non-deterministic failures. To solve the problem, we extend a combined maintenance and routing (CMR) optimization approach which is a procedure based on two components: (a) first a maintenance model is used to determine the optimal time to perform PM operations for each site and second (b) a mixed integer program-based split procedure is proposed to route a set of crews (e.g., sewer cleaners, vehicles equipped with winches or rods and dump trucks) in order to perform PM operations at a near-optimal minimum expected cost. We applied the proposed CMR optimization approach to two (out of five) operative zones in the city of Bogotá (Colombia), where more than 100 maintenance operations per zone must be scheduled on a weekly basis. Comparing the CMR against the current maintenance plan, we obtained more than 50% of cost savings in 90% of the sites.

Determination of Microstructure-Based Constitutive Models Using Temperature Rise Distribution in Plane Strain Machining

Predicting flow stress at high strain-rates is a desirable practice for material behavior characterization. Sub-grain size has shown a huge influence in cutting forces and the workpiece surface finish determination during orthogonal cutting process. Hence, a prediction of flow stress as a function of thermomechanical conditions and sub-grain size is of great important which is studied in this work for OFHC copper. The principal thermomechanical conditions being strain, strain-rate and the accompanying temperature rise are characterized in Plane Strain Machining (PSM) and the resulting microstructure, sub-grain size, is quantified. Material maximum flow stress (a constitutive model) as a function of thermomechanical conditions and sub-grain size is predicted considering a saturated state in microstructure using optimization algorithms for reaching the validated temperature rise based on modified Hahn’s model. Evaluated models suggest a major influence of strain-rate and dislocation in temperature rise estimation and flow stress prediction leading to consideration of mechanical failure phenomenon involved in machining-based manufacturing processes.

A Prioritization Tool for SUDS Planning in Large Cities by Coupling an Urban Drainage Model with Mixed Integer Linear Programming

Decision making regarding Sustainable Urban Drainage Systems (SUDS) sitting is an analytical complex process, as it involves the evaluation of a high number of environmental, physical and technical considerations. Additionally, as the resources are always limited (e.g. budget and land availability), the prioritization of sub-catchments for SUDS placement would help decision makers to determine where is most beneficial to locate these infrastructures. This study proposes a methodology that couples an urban drainage model and Mixed Integer Linear Programming (MILP) to determine where is more beneficial to locate SUDS to reduce both runoff volumes and combined sewer overflows (CSOs). To achieve this goal, the City Drain model is used to model the runoff generation and the flows among sub-catchments. Three indexes are proposed to quantify the reduction on both CSO and runoff volumes, and a lexicographic multi-objective model is used to find the prioritized sub-catchments within a city. The methodology was applied to sub-catchments of Bogota (Colombia), comprising an area of 38 km2. Preliminary results showed that the prioritized sub-catchments were highly dependent on land availability and the optimal solution did not necessarily involve the selection of the sub-catchments that yield most runoff. This study demonstrates the importance and usefulness of the prioritization tool for SUDS planning, which can be used by other large cities like Bogota.

Análisis de uniones adhesivas con base de poliuretano sometidas a cargas cuasiestáticas y cíclicas

Adhesively bonded joints using polyurethane base adhesive are very common in the marine, automobile and construction industry. All these types of applications evidence the necessity to know the response of these joints under static and fatigue conditions. The aim of this work is to experimentally analyze this type of joints, under static and cyclic loads, considering geometric joints variations, substrate surface pre treatments and time of exposition in highly moisture environments.