Examensarbete

Utveckling av avrinningsmodell för gröna tak genom linjär och icke-linjär reservoar-modellerna

Gröna tak har visats lovande för framtidens dagvattenhantering i urbana områden och kan minska den årliga avrinningen med 50 % genom avdunstning, tillfällig magasinering och fördröjning. Därför är det väldigt viktigt att förstå gröna taks funktion och att kunna modellera avrinningen på ett vettigt sätt utan att blanda in för många svåruppskattade parametrar såsom konduktivitet och diffusivitet för jord och dylikt.

Det här examensprojektet syftar till att tillämpa avancerade hydrauliska verktyg för att simulera avrinningen från gröna tak genom att kalibrera endast två parametrar för icke-linjär reservoar metoden. Dessa parametrar skall senare jämföras mot data över tak för att studera eventuella samband och korrelationer.

Proposal for master thesis in Water and Environmental Engineering:

Who should apply?
Students studying their last year in Environmental or Civil Engineering programs are encouraged to apply. The applicants are expected to be knowledgeable about basic urban hydraulics and hydrology. Some knowledge of advanced hydraulics is recommended but not mandatory. Students should also be competent in using Microsoft Excel (or even Matlab) for the modelling work.

 

Aim
Reservoir models (linear and nonlinear) are known hydraulic tools that can be used for modelling rainfall-runoff in catchment areas. Earlier literature shows that these methods can also be applied on green roofs which result in reasonably decent output if calibrated well. The student(s) in this master thesis project will evaluate the application of linear and/or nonlinear reservoir models on existing data from green roof rainfall-runoff experiments.

Method
Data required for the project is supposed to be derived via an extensive literature study. Data acquisition through digitization of graphs in the published material will in most cases be inevitable to use. Along with application of reservoir models, calibration and parameter estimation, the students are also supposed to document the physical parameters associated with the structure of the studied green roofs (i.e. slope, drainage layer’s thickness, type of vegetation, soil layer, initial moisture content, etc.). This documentation will then be used for investigation of possible correlations between green roof characteristics and model parameters.

Background
Green roofs are classified as techniques within the framework of blue-green solutions for management of storm water in urban areas. These structures can, according to the existing research results, reduce annual runoff volume by about 50% as average through facilitated evapotranspiration, detention, as well as retention. Green roof seems to be a very promising solution for storm water handling problem of cities with regards to the climate change scenarios considering that about 40-50% of the impervious surfaces of residential areas in cities are roofs. Additionally, roof area is considered as a dead surface which can be used for effective storm water management without competing with other urban land applications.

However, the knowledge regarding the detailed function of green roof is not highly developed. Different models have been suggested for simulating rainfall-runoff relationship from green roofs which in most cases are computationally too complex to be handled, especially when it comes to estimation of parameters. Parameters such as soil conductivity, diffusivity are too sophisticated to be quantified for daily modeling purposes. Therefore there is a need to develop conceptual models that can simulate the behavior of green roofs in a more practical and less demanding manner.

Contact
Salar Haghighatafshar, Ph.D. student in Water and Environmental Engineering, LTH Salar.Haghighatafshar@chemeng.lth.se (Tel. nr. 046-222 8998)
Jes la Cour Jansen, Professor in Water and Environmental Engineering, LTH Jes.la_Cour_Jansen@vateknik.lth.se (Tel. nr. 046-222 8999)