Urban Flood Models in Athens
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Questions and Answers

What is one of the parameters used to define a subcatchment in combined sewer systems?

  • Land cover type
  • Water table depth
  • Width (m) (correct)
  • Soil type

Which type of pipes is newer in the drainage system described?

  • Circular pipes (correct)
  • Rectangular pipes
  • Egg-shaped pipes
  • Open ditches

What is the average slope range for the pipes mentioned in the content?

  • 2.0 to 5.0 %
  • 0.6 to 10.8 % (correct)
  • 0.6 to 1.5 %
  • 3.0 to 10.8 %

How was the width of the subcatchments calculated?

<p>Area divided by average maximum length (A)</p> Signup and view all the answers

Which model is used for dynamic rainfall-runoff simulation?

<p>EPA-SWMM5 (D)</p> Signup and view all the answers

What parameter range was determined using appropriate tools in ArcGIS?

<p>Slope of the subcatchments (D)</p> Signup and view all the answers

What depth range do egg-shaped pipes fall within in the drainage system?

<p>0.9 to 2.4 m (D)</p> Signup and view all the answers

Which parameter indicates the percentage of the land that does not absorb water?

<p>Percent impervious (B)</p> Signup and view all the answers

What is the primary advantage of using 1D-2D coupled models over 1D-1D models?

<p>They provide more accurate simulations of flood extent. (C)</p> Signup and view all the answers

Which tools are used in the 1D-2D modeling approach for urban flooding?

<p>MIKE URBAN and MIKE FLOOD (D)</p> Signup and view all the answers

In the 1D-1D modeling approach, which system is combined with the sewer system?

<p>1D surface models (C)</p> Signup and view all the answers

What is one limitation of using the 1D-1D model for urban drainage?

<p>It cannot model flood inundation accurately. (C)</p> Signup and view all the answers

Which area was targeted for the assessment of urban flooding in this study?

<p>Ano Patisia, Kypseli in Athens (B)</p> Signup and view all the answers

What is the basis for the 1D-2D coupled models?

<p>1D-SWE and 2D-SWE (D)</p> Signup and view all the answers

What challenge is faced due to the ungauged nature of the site?

<p>Inability to measure flow in the pipes. (C)</p> Signup and view all the answers

Which system's interactions are important when modeling urban drainage networks?

<p>Sewer and surface systems (A)</p> Signup and view all the answers

What method was selected for hydrologic calculations in each subcatchment?

<p>Kinematic Wave Method (A)</p> Signup and view all the answers

For which return periods were the volumes calculated using the 1D-2D model?

<p>10 and 25 years (C)</p> Signup and view all the answers

Which loss model was chosen in the study?

<p>Horton’s Equation (B)</p> Signup and view all the answers

What engine does the 1D-1D model use for hydraulic computations?

<p>SWMM (A)</p> Signup and view all the answers

What was simulated with the orifice equation in the 1D-2D model?

<p>Overflow from manholes (D)</p> Signup and view all the answers

What was the maximum depth of water in the surface network according to the 1D-1D model simulations?

<p>0.10 m (A)</p> Signup and view all the answers

What is the primary reason for differences in flow between the two models?

<p>Different simulation engines utilized (B)</p> Signup and view all the answers

Which of the following describes the grid cell configuration used in the 2D model?

<p>5x5 m square cells (D)</p> Signup and view all the answers

What is the range of Manning's N for impervious areas?

<p>0.013 to 0.014 (C)</p> Signup and view all the answers

What does Dstore represent in relation to impervious areas?

<p>Depth of depression storage (A)</p> Signup and view all the answers

What is the range for the percentage of impervious area represented by %Imperv?

<p>45 to 90 (A)</p> Signup and view all the answers

What key advantage does MIKE URBAN have over SWMM5?

<p>GIS integration capabilities (B)</p> Signup and view all the answers

What is the value range for the Curve Number (CN)?

<p>77 to 94 (D)</p> Signup and view all the answers

The width of subcatchments can range from which values?

<p>7.93 to 162.77 m (B)</p> Signup and view all the answers

What does the term '1D-1D model' refer to in MIKE URBAN?

<p>One-dimensional flow in one-dimensional space (B)</p> Signup and view all the answers

What is the significance of the IDF curve in the context of MIKE URBAN simulations?

<p>It is used to determine rainfall intensity over time. (B)</p> Signup and view all the answers

What is the main purpose of comparing the 1D-1D urban flood model with the 1D-2D model?

<p>To demonstrate the importance of model structure (C)</p> Signup and view all the answers

Which model was found to be faster in the simulations?

<p>1D-1D model (C)</p> Signup and view all the answers

What is a limitation of the 1D-1D model in flood simulations?

<p>It cannot simulate flood extent and inundation accurately (D)</p> Signup and view all the answers

What was one of the objectives of the sensitivity analysis in the 1D-2D model?

<p>To experiment with different building representation methods (D)</p> Signup and view all the answers

Which factor was considered for simulation regarding rainfall in the study?

<p>Return periods of 10 and 25 years (D)</p> Signup and view all the answers

What kind of model was used in the comparison for simulating urban flooding?

<p>1D-1D and 1D-2D models (B)</p> Signup and view all the answers

Who provided the software and free licenses for the MIKE models used in the study?

<p>DHI (A)</p> Signup and view all the answers

What is one element that could affect the simulation accuracy in 1D-2D modeling?

<p>Approaches for building representation (C)</p> Signup and view all the answers

What is the primary focus of the proceedings from the symposium held in Reykjavik?

<p>Modeling urban floods and drainage (B)</p> Signup and view all the answers

Which modeling package is associated with flood risk assessment in the provided content?

<p>MIKE URBAN (B)</p> Signup and view all the answers

Which publication provides a user guide for MIKE FLOOD 1D-2D Modelling?

<p>DHI (2016c) (B)</p> Signup and view all the answers

What methodology was described by Tsakiris (2013) in the context of urban flood management?

<p>Flood risk assessment (B)</p> Signup and view all the answers

What does the acronym SWMM stand for in relation to urban stormwater management?

<p>Storm Water Management Model (D)</p> Signup and view all the answers

Which study evaluated inundation risks in urban drainage systems?

<p>Zhu et al. (2016) (D)</p> Signup and view all the answers

What is the purpose of the desktop review mentioned in the content?

<p>To review 2D hydraulic modeling packages (B)</p> Signup and view all the answers

What type of environment is specifically addressed by Pistrika et al. (2014) in their study?

<p>Built environments (B)</p> Signup and view all the answers

Flashcards

1D-1D model

A model that couples sewer and surface systems using SWMM, treating both as one-dimensional systems.

1D-2D model

A model that couples sewer and surface systems using MIKE URBAN and MIKE FLOOD. It uses 2D modelling for surface water and 1D for sewer water.

Urban Flooding

Flooding in urban areas due to combined sewer and surface water systems, often caused by heavy rain.

MIKE URBAN-MIKE FLOOD

A software package used to create a 1D-2D model, simulating both sewer and surface flows.

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SWMM

Storm Water Management Model used for 1D-1D urban drainage modelling.

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Ano Patisia, Kypseli

Small urban catchment in Athens, Greece used for testing urban flooding models.

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2D-SWE

Two-dimensional model for surface water.

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1D-SWE

One-dimentional model for water flow in sewer pipe networks

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Subcatchment parameters

Key characteristics of a subcatchment area in a combined sewer system, used in SWMM software for rainfall-runoff simulation.

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SWMM software

A hydraulic model used to simulate rainfall-runoff processes in drainage systems.

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Area of subcatchment

Size of the area that drains rainfall into a combined sewer. Measured in hectares.

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Width of a subcatchment

Calculated as the area divided by the average maximum length.

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Slope of pipes

The gradient of the sewer pipes, influencing water flow. Ranges from 0.6 to 10.8% in the system

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Impervious Percentage

The proportion of the subcatchment surface that doesn't absorb water (e.g., roads, roofs).

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Manning's n

A coefficient that describes the roughness of the pipe surface. Affects water flow resistance.

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Depression storage

Water retained in depressions (low spots) on the ground before flowing into the sewer.

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N-Imperv

Manning's N value for impervious surfaces like roads and pavements.

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N-Perv

Manning's N value for pervious surfaces like grass and soil.

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Dstore-Imperv

The depth of depression storage (water held in puddles) on impervious surfaces.

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Dstore-Perv

The depth of depression storage on pervious surfaces.

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CN

Curve Number, a value representing the runoff potential of a watershed.

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MIKE URBAN

A software used to simulate water flow in urban sewer and surface systems, using 1D modelling for sewers and 2D for surface water.

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MIKE FLOOD

A software used to simulate surface water flow in 2D, complementing MIKE URBAN for a complete urban drainage model.

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Kinematic Wave Method

A simplified method to calculate flow in a subcatchment, considering only area, imperviousness, and slope.

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Horton's Equation

A method for calculating infiltration losses in a subcatchment.

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Orifice Equation

A formula used for calculating flow between the sewer and surface systems, specifically for overflows from manholes.

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Combined Sewer System

A system where wastewater and stormwater flow in the same sewer pipes.

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Return Period

The average time interval between occurrences of a specific event (e.g., heavy rainfall) of a certain magnitude.

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Storm Duration

The total time period that a storm event lasts.

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Model Comparison

The study compared two models, SWMM (1D-1D) and MIKE URBAN-MIKE FLOOD (1D-2D), for simulating urban floods.

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Why Choose 1D-2D?

The study chose 1D-2D because it provides more accurate flood extent and inundation simulation compared to 1D-1D.

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Athens' Catchment

The study focused on simulating floods in a small urban catchment (Zone D) in Athens to test model accuracy.

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Sensitivity Analysis

This involved examining the impact of changing different model inputs on flood simulation results.

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Building Representation

The study experimented with different ways to model buildings in the 1D-2D model to see how it impacts flood simulation.

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Flood depth-damage function

A relationship that describes the impact of different flood depths on infrastructure and buildings.

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Study Notes

Urban Flood Models

  • Comparing 1D-1D and 1D-2D models for urban flooding assessment is the study's focus
  • The study uses a small urban catchment in Athens, Greece (Ano Patisia, Kypseli) as a case study
  • 1D-1D approach combines sewer and surface systems using SWMM, a model simulating flow in both systems as a set of links and nodes (1D Shallow Water Equations - 1D-SWE)
  • 1D-2D approach couples surface and sewer systems using MIKE URBAN and MIKE FLOOD, solving 2D-SWE for the surface system and 1D-SWE for the sewer system
  • Results highlight the importance of considering sewer and surface interaction in urban drainage models
  • 1D-2D models are better for simulating flood extent and inundation, overcoming limitations of 1D-1D models

Case Study Details

  • The study area (Ano Patisia, Kypseli) is a highly urbanized and impervious area with an area of 89 hectares.
  • Catchment comprises 112 nodes and 79 combined sewer pipes with a total length of about 5 km.
  • Drainage system includes both circular (newest) and egg-shaped (older) pipes.
  • Pipe slopes range from 0.6% to 10.8% (average 3%)

Modelling Methods

  • SWMM (Storm Water Management Model): Dynamic Wave (DW) model for hydraulic calculations, Curve Number (CN) method for infiltration.
  • Key SWMM parameters: subcatchment area, width, slope, imperviousness percentage, Manning's 'n', and depression storage
  • MIKE URBAN-MIKE FLOOD: MIKE URBAN uses 1D-SWE (MOUSE/MIKE11) for pipe flow, SWMM functionality, GIS integration, 2D simulation capability via coupling with MIKE FLOOD. MIKE FLOOD uses structured grid (2D-SWE), coupled with MIKE URBAN to simulate combined drainage system interactions. An orifice equation is used to model flow exchange between 1D and 2D models.
  • Kinematic Wave method and Horton's equation are selected for hydrologic and loss calculations.
  • Simulation parameters: Intensity-Duration-Frequency (IDF) curves, 1-hour duration rainfall events for 10 and 25-year return periods

Results and Discussion

  • 1D-1D and 1D-2D models produce similar runoff volumes, but differences exist in sewer flows.
  • The 1D-1D model is potentially faster compared to the 1D-2D model
  • 1D-2D model accurately predicts flood extent and inundation.
  • 1D-2D model simulations calculate water depth and flow velocity at locations
  • 1D-1D model overestimates surface water flow, especially when sewer capacity is exceeded; it doesn't model overflow from manholes accurately, as this is often an artifact of the way the model calculates water surface profiles in open channels.

Conclusions and Recommendations

  • 1D-2D models are better for predicting flood extents and inundation compared to 1D-1D models, despite being slower to run
  • Further research suggests incorporating rainfall-runoff monitoring, sensitivity analysis for 1D-2D models, and improved representation of structures like buildings.

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Description

Explore the comparison between 1D-1D and 1D-2D models for urban flood assessment, focusing on a case study in Ano Patisia, Athens. Understand how these models integrate sewer and surface systems to analyze flooding dynamics and inundation extent in a highly urbanized area.

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