Integrated Urban Hydrology is it so different from rural hydrology? what is the problem? available modeling approaches

Lars-Göran Gustafsson

Head of Innovation, DHI Sverige AB

Rural versus Urban hydrology – Any similarities?

A natural river stream versus a leaking pipe?

Observed daily discharge in Kungsbackaån

Rural versus Urban hydrology - similarities

Discharge in Kungsbackaån Inflow to treatment plant

Observed daily inflow to treatment plant

Seasonal variation for a year

Rural versus Urban hydrology - differences

Connected impervious areas

Indirect effect from precipitation

Faster response to rain!

Observed high resolution inflow (l/s) to treatment plant

a 24-hour zoom

The problem

• Yearly volume >50% of total wastewater volume

• Daily extremes >90% of total wastewater volume

• Growing problem (+100 % over 50 years in some areas)

• Overloaded wastewater treatment plants (WWTPs)

• Sewer overflow of untreated wastewater to receiving waters

• Overloaded sewer networks with flooding problems

• High energy consumption for pumping stations

Hydrological flow

components in

sewer systems

creates …

Connected surface Over leak Drain flow Infiltration/leakage

fluktuation

volume

Sources to hydrological flow components in sewer systems

Affected by: • Condition of sewer system • Type of system and layout • Topography • Geology • Meteorology

As for rural hydrology

Can a lumped conceptual modeling approach be useful?

MIKE URBAN RDI-module

Combined sewer system in a city center

Impervious areas

Infiltration to sewer system Sanitary flow

Yes! To define flow components

Combined sewer system located in discharge area along a river

Impervious areas

Infiltration to sewer system Sanitary flow

Yes! To define flow components

Old sanitary sewer system in bad condition

Impervious areas

Infiltration to sewer system Sanitary flow

Yes! To define flow components

Measures

implemented

… and for follow up after measures

Measures

implemented

Hydrological model calibration period

… and for follow up after measures

Hydrological model calibration period Simulation after measures implemented

Measures

implemented

Difference

interpreted as

effect of

measures

… and for follow up after measures

Effect of

measures

Observed and simulated cumulative volumes, Oct 2007 – June 2009

Measures

implemented

… and for follow up after measures

Disconnection of impervious areas from sanitary sewers

Relining of sewers and manholes

Construction of new drain schemes

Blue/green storm water management (swales, infiltration)

Predicting effects from alternative alleviation schemes?

drainflow

leakage

infiltration

runoff

rain

evaporation

infiltration

MIKEURBAN

MIKE SHE

MIKEURBAN

MIKE SHE

MIKE SHE

Predictions demand a physical and distributed model approach

MIKESHE + MIKEURBAN

Red areas are strong discharge areas with high need for drainage

… allows identification of discharge areas with high drain needs

Case from Vittskövle, Kristianstad

With urbanization

Sewer system

ARV

Vittskövleån

Natural conditions

Above ground

High

Medium

Low

Groundwater level

… allows description of natural conditions

… allows prediction of effects from measures

Før og efter etablering af dræn

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

lite

r/s

ek

Dræn-pumpe afbrudt

Områdesdræn

spildevandsledninger

ARV

Tilløb ARV inden tiltag Tilløb ARV efter tiltag Pumpeflow fra drænledninger

Case from Vittskövle, Kristianstad

… allows separation of pluvial floods and groundwater floods

Case from Vänersborg, close to Lake Vänern

Exploitation area Catchment area and topography

Lake Vänern bedrock/sand dunes

clay

High discharge from mountain plateau

Exploitation area

Lake Vänern

Enclosed area

… allows separation of pluvial and groundwater floods

Groundwater flood during wet season Pluvial flood from a 100-year cloudburst

Case from Vänersborg – Natural conditions

… allows separation of pluvial and groundwater floods

Groundwater flooding during wet season Pluvial flood from a 100-year cloudburst

Case from Vänersborg – Future with alleviation scheme

To conclude

Urban hydrology has many similarities with rural hydrology – but more complex!

Lumped/conceptual models are useful to: analyze sources for hydrological flow components distinguish between effects of measures and hydrological variations evaluate climate change effects

Physical/distributed models are needed for: predictions of physical changes analyses of spatial differences deeper analyses of physical behavior

9 March, 2017 © DHI #24

TACK !