Hydrologic Sensitivity Analysis – Contribution to the Assessment of Effectiveness of SUDS in Small Urban

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IAHR 2009

Hydrologic Sensitivity Analysis – Contribution to the Assessment of Effectiveness of SUDS in Small Urban

Catchments

S. Hellmers

E. Pasche, N. Manojlovic,, C. Brüning, N. Behzadnia

Vancouver, August 2009

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Agenda

• Introduction

• Theoretical Approach of modelling SUDS

• Implementation in a rainfall runoff model

• Testing in a case study

• Conclusions and Outlook

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1. Introduction

Flood Risk Management in Small Urban Catchments:

+

Pluvial Fluvial

=

Flooding in Small Urban Catchments of up to 50 – 70 km²

Need to cope with uncertainties derived by:

• Future Urban Development

• Climate Change Aspects

Focus on adaptive responses:

• Non-structural measures

• Flood Resilience Measures

• Flood Probability Reduction measures

 e.g. Sustainable Drainage Systems (SUDS)

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1. Introduction

Sustainable Drainage Systems (SUDS‘s) :

• Source Control Measures (e.g. green roofs)

• Detention structures (e.g. Ponds, Swales)

• Infiltration Techniques (e.g. Filter drains, Soakaways)

• Combined measures: (e.g. Swales with filter drains)

Objectives of the work:

 Quantifying the Hydrologic Effects of SUDS‘s in Small Urban Catchments at extreme storm events.

 Developing a new method to evaluate the effectiveness of SUDS on a catchment level

 Testing and verifying this new concept.

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Water level (h) in the swale

Soil moisture (sw) : Funktion of Q_drain:

2. Theoretical Approach

Cross section of a Swale -Filter- Drain system

swale overflow p

eff inflow

inflow

A

(t) (t) Q

ET perk(t)

(t) A P

(t) Q

t

h(t)     



) ,

d , f(h

(t)

Q

_Drain  _sat,_FL _pipe



_pipe

swale drain

a

A

) ( - Q

(t) ET perk(t)

inf(t) t

sw(t)

t



 



P_eff

L1 L2

Perk1 Filter layer

L3

L4

Swale

Theoretical approach:

Subdivision of the SUDS-unit into 4 layers

Colmation Layer

Base Layer

Groundwater recharge

FL

h

sat,

) ,

(d_pipe _pipe

(t) Q

_Drain

(t) Q

_Overflow

(t)

P

_eff

(t)

Q

_inflow

ET

_P

(t)

perk(t)

perk(t) Free water

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3. Implementation

Urban

Development areas with the attributes of SUDS

Reality

SUDS defined on properties One sub-catchment

Local SUDS on properties with defined

parameters by the planer

Model

Representation in the data model

Urban

development areas

Data Input of SUDS by the Planer (e.g.):

• total area of SUDS =

• Percentage of area connected to the SUDS

• Average depth of swale and filter drain

• Average permability of the soil layers

• Size and elevation of the drain pipe

Integrative approach to model SUDS on the catchment level

total SUDS,

A

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Aggregation of SUDS per Hydrotop

3. Implementation

Hydrotopes

Hydrotope SUDS

with area A_i

Data Processing in a Rainfall Runoff Model

Land use areas With SUDS attributes

=

Hydrogeological units (Pedology and hydrology)

+

SUDS are introduced as Hydrotopes

Intersection

total SUDS, 2

n

1 i

i

A

A 





Hydrotopes: hydrological similar response units with the specific pedology, hydrology and runoff characteristic

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4. Testing : Planning Scenario Swale

• Implementation in the rainfall runoff model Kalypso Hydrology

• Case Study area: Garforth, West Yorkshire in England

Swale 1002 Swale

1011

Swale 2010

Reference: Gill,2008

DEFRA Pilot Project Area:

Garforth

Swale location:

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4. Testing : Planning Scenario Swale

• Implementation in the rainfall runoff model Kalypso Hydrology

• Case Study area: Garforth, West Yorkshire in England

Swale 1002 Swale

1011

Swale 2010

Reference: Gill,2008

DEFRA Pilot Project Area:

Garforth

Land use area with

SUDS attributes:

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4. Testing : Planning Scenario Swale

Max. Flood Peaks:

Flow Monitor data : 0.36 m³/s Model Results : 0.33 m³/s Difference : 8%

Flood Volume:

Flow Monitor data : 2888 m³ Model Results : 2614 m³ Difference : 9%

Calibration Result of the Rainfall Runoff Model in Kalypso Hydrology

Model data results Flow monitor data

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4. Testing: Planning Scenario Swale

Simulation results of the model with and without the Planning Szenario Swale

Flood Peaks:

Without Swale: 96 l/s With Swale : 74 l/s

Flood Peak Reduction: 23 %

Flood peak without swale: 0.096 m³/s

Flood peak with swale: 0.074 m³/s

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4. Testing - Water Balance in the Swale - Unit

Balance Volume [m³]

Inflow swale + 482.1 Outflow Drain - 391.9 Perkolation - 0 Storage in

swale and Filter

- 86.2

Evapotrans- piration

- 4.4

Diff. - 0.4

Free water in Filter Layer

Base Layer saturated

Water depth swale

Q _drain

Inflow into swale:

•eff. precipitation +

•runoff from sealed areas [mm]

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5. Conclusions and Outlook

Conclusion:

• A physically sound concept with a high level of detail in describing the hydrological processes in SUDS has been implemented in a rainfall runoff model.

• The new method enables the planner to define the Input data in an easy way via attributes of land use.

• First testing confirms the method of the new approach and

demonstrate the effect of SUDS on the flood hydrograph on the catchment level.

Outlook:

• Extensions to further types of SUDS Systems: e.g. green roofs draining into swales.

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Acknowledgment:

The Pennine Water Group (University of Sheffield) provided the hydrological and pedological data for the Rainfall Runoff Model in the case study.

Thank you for your Attention!

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IAHR 2009