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STUDY OF THE STORM DRAIN SEWER OF THE URBAN CATCHMENT OF LA RIERETA, SAN BOI DE LLOBREGAT, SPAIN. TEAM 3: 1 . Aline Veról 2. José Rivero 3. Pedro Ramos 4. Ramiro Pighini. 07.2012. Introduction.
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STUDY OF THE STORM DRAIN SEWER OF THE URBAN CATCHMENT OF LA RIERETA, SAN BOI DE LLOBREGAT, SPAIN TEAM 3: 1. AlineVeról 2. José Rivero 3. Pedro Ramos 4. Ramiro Pighini 07.2012
Introduction The traditional canalization approach for flood control has been complemented or replaced by new concepts that consider a systemic approach, with distributed interventions over the catchment intending to recreate flow patterns prior to the urbanization. LID measures have been proposed to fulfill this aim. The spatio-temporal variability of the phenomenon gives particular characteristics to each catchment. In this context, a systemic evaluation of flood control projects is needed, providing adequate spatial coverage without superimposing effects in time. Mathematical modeling emerges as a useful tool to represent the integrated behavior of urban drainage and landscape.
Objective The general objective of this project is to perform an analysis on the model of the storm drain sewer of “La Riereta”, an urban catchment located in Spain, and propose a sewer rehabilitation process. To carry out this process, a hydrological and hydraulic model will be developed using the EPA Storm Water Management Model (EPA SWMM 5.0).
LID – Low Impact Development LID: Aset of procedures that try to understand and reproduce hydrological behavior prior to urbanization. The main principles of this approach may be briefly described by the following points: • Minimise runoff, acting on impervious rates reduction and maintaining green areas; • Preserve concentration times of pre-development, by increasing flow paths and surface roughness; • Use of retention reservoir for peak discharge control and improve water quality; • Use of additional detention reservoirs to prevent flooding, if necessary.
Examplesof LID measures Bio retention Infiltration trenches
Examplesof LID measures Vegetated roof covers Permeable pavements
Examplesof LID measures Rain Barrels
Methodology • To develop the proposed case study, the group followed the methodology suggested by the organizers and detailed below: • Basin discretisation; • Determination of the input data (for sub-catchments, conducts and manholes); • Calibration and validation of the model using three different rain events and hydrographs registered at the outlet of the urban basin; • Determination of the design rainfall for TR 10; • Simulation of the drainage network diagnosis; • Analysis of the catchment to evaluate and propose the use of LID measures; • Simulation of the drainage network considering the implementation of the proposed LID measures; • Analysis and discussion of results.
Case Study The present case study is an urban catchment located in SantBoi de Llobregat, a town near Barcelona, Spain. This catchment has a surface area of approximately 17 ha and it presents high indexes of impermeability. Its slope varies from high to medium values. Roof drainage discharges directly to the streets through downspouts. Additionally, a group of inlets distributed in the streets ensure the collection of the generated runoff after the occurrence of rainfall. The drainage system of “La Riereta” is a combined sewer network and it is mainly composed by circular cross-section pipes with different diameters and made by concrete.
Results - Rainfall Three different rainfall events, with their corresponding flows – measured at the catchment outfall – were assigned for each group. Each of these events is identified by the name of the saint of the day in which the registration started.
Results - Calibration/Validation The chosen rainfall events for calibration of the model were: Susana and Efrén.
Results - Calibration/Validation Santa Cecilia rainfall event was used to validate the model
Results - Diagnosis of drainage network Once the model was calibrated and validated, the team modelled the diagnosis of the drainage network for a design rainfall. A design rainfall of 10 years of recurrence time is used not only in the city of Barcelona, but also in some municipalities around it, like SantBoi de Llobregat. In this case, the design rainfall should be obtained from the IDF curve Barcelona-Fabra, based on precipitation series registered between the years of 1927-1993. This IDF curves are described by the following expressions: Where: I: (mm/h) T: (years) D: (minutes)
Design rainfall obtained for TR 10 mm/hr. min.
Results - Diagnosis of drainage network • LID measures: Porous pavements, Bio retention cells and Rain barrels
Conclusions • The calibration of the model showed a reasonable result, but the validation showed an exaggerated over estimation in the total volume. • Considering the design rainfall, the nodes N4, N7 and N10 surcharged. • The main purpose of this work was to treat this flooding problem using the LID concept. • The use of LID, such as permeable pavements, rain barrels and bio retention cells, showed a good result on the main drainage line, where the actions in the catchment context are more sensible. The nodes that were flooded in the borders of the catchment were less sensible to LID measures because the surfaces related to these nodes were small and the distributed measures could not be as effective as they were in the catchment context.
Conclusions • Another problem was that in the borders of the catchment there may occur, in reality, a diversion to the neighbouring catchments. As it has not been considered in the modelling, possibly the discharge in these nodes may be overestimated. • This problem may also be the explanation for the calibration/validation results. • In a real situation, a good result could be achieved by the use of LID combined with other flooding control measures. As an example, detention catchments or drainage net rehabilitation could be jointly considered.
