water quality dynamics in semiarid regions with temporary

Palermo - 2004 Water Quality Protection and ManagementProf. Dr.-Ing. habil. Herwig LehmannUniversity of Hannover

Jochen Froebrich

Water quality dynamics in semiarid regions with temporary streams

Water quality dynamics in semiarid regions with temporary streams

Jochen Froebrich

Water quality protection and management group,University Hannover, Germany

specialized in water management problemsfor semi-arid regions (MENA, Central Asia)

Co-ordinator of tempQsim

Domain leader water availability, AQUASTRESS

availability of safe water resources by combined water quality and quantity management

introduction

•to introduce the project tempQsim

•typical water quality dynamics intemporary streams

•outline of future mitigation options

•conclusions for modelling strategies

structure

Rational

In many water stressed regions world wide: • water use from reservoirs at risk due to

eutrophication and toxic algae blooms

• reservoir capacity losses by sedimentation

adapted quality mangement needs knowledgeon pollution pathways and adapted management tools

EU-WFD & EU-WIMC adresses improvement of water quality in the framework of IWRM

tempQsim in brief

water quality dynamics

Intermittent streams:are dry part of the year, but contain flow when the groundwater is high enough as well as during and after a storm event.

Ephemeral streams:contain water during and immediately after a storm event but are dry the rest of the year.

tempQsim in brief

temporary watersforms a major part of the catchments

about 40% of all catchments in Greece(after Nikolaidis et al. 2004), much higher with consideration of dry tributaries

despite this fact, very vew knowledge on water quality dyanmics, ecosystem functioning and available modelling tools

about 100% in the southern part of Sardinia

large number of ramblas in Spain

tempQsim in brief

objectives:

I N S T IT U T D E R E C H ER C H E P O U RL E D E VE L O P P E M E N T

•to test a number of catchment models in study sites with temporary waters

•to develop detailed conceptual models for each study sites (sediment and water phase)

•to improve modelling tools for its applicability in semi-arid basins

tempQsimtemptempQQsimsim

Dry Months (rf / pet < 0.3)

dry_monthsValue

0

1

2

3

4

5

6

7

8

9

10

11

12

Degebe

El Albujon

Véne

Mulargia

Tagliamento Iskar

Krathis

(Irvine, 2004)

Dry Months (rf / pet < 0.3)

dry_monthsValue

0

1

2

3

4

5

6

7

8

9

10

11

12

Degebe

El Albujon

Véne

Mulargia

Tagliamento Iskar

Krathis

(Irvine, 2004)

Vallecebre

tempQsim in brief


Seasonal sequence

time

wat

er le

vel

sediment

transport

evaporationinfiltration

resuspensiontransport

micriobiological transformations

accumulation

first flush effectfirst flood event


00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00

20

40

60

80

100

120

140

160

180

22. October 2003

Wat

er le

vel,

cm

Water level

0

20

40

60

80

100

120

140

160

PN

PN, m

g/l N

0

2

4

6

8

10

12

14

PP

PP, m

g/l P

first flush effects

Mulargia, SITE B

Diliberto, Botti, 2004

22.10.2003 21.11.2003 28.01.2004 29.02.2004 17.04.2004 05.05.2004

20

40

60

80

100

120

140

160

180

Date

Wat

er le

vel,

cm

Water level

0

20

40

60

80

100

120

140

PN

, mg/

l N

PN

0

2

4

6

8

10

12

14

PP

, mg/

l P

PP

imortance of first flood events

Mulargia, SITE B

Diliberto, Botti, 2004



OUTLET

karstic areas agricultural areas urban areas

springs urbandrainage system

RIVER

ACCUMULATION REACHES

WWTP

naturaldrainage system

ACCUMULATION RATESduring drying period1 kg-TP/day - 6 kg-TN/dayin the pools3 kg-TP/day - 8.5 kg-TN/day

DENITRIFICATION RATES25 µg-N-NO3/dayOM in sediments1 – 6 %

Marie George Tournoud, Jean-Louis Perrin, 2004

Dry period


OUTLET


springs urban²drainage system

RIVER


1st FLOOD

3 % runoff coefficient

36 % runoff coefficient3-6 hours duration


OUTLET


springs urbandrainage system

RIVER


2nd FLOOD

3 % runoff coefficientat the outlet

duration: less than 1 daypeak flow: 0.5 – 10 m3/s

velocity: 0.6 – 1.1 m/s⇒ 45 to 50 mn time transfert

high initial losses




Relatively smallcompared to 2nd

flood,significant increase for NH4 , particulate nutrients

Significant30% of annual TSS,10% of total Discharge

Urban stormwater, remobilisation of mass, no discharge at the outlet

Significant for Ptot compared to other floods

KrathisMulargiaVeneAlbujon

major contribution of 1st flood to total load &runoff


Significant for all particulate nutrients, increase in NH4NO2, DON & DOP

Only for an exceptional spring flood

The 2nd flood produces the first discharge that reaches the catchment outlet

Indication of high NO3-Nrelease

KrathisMulargiaVeneAlbujon

major contribution of 2nd or later flood

Conclusions

Storms are dominant drivers causing pollution remobilisation and transport

• erosion and washing pollutants from land surfaceare important pathways in sloping areas

• instream resuspension of waste wateroriginated organic matters and nutrients

Conclusions

Accumulation during dry period

contribute to resuspension of waste water originated organic matters and nutrients

Accumulation of sewage water discharge

Accumulation on land side manure, animal faecals, plant residues,nutrient enriched topsoil

Spatial and temporal variability of loads and fluxes

•most important constraint for existing modelling tools

•attractive starting points for practical measures

Conclusions

simulation of purification processes, short time consideration of pollution variability

identification of potential events

settling pondspre-dams

simulation of impact, evaluation of investment efficiency

significance ofpollution pointsources

sewage water treatment

simulation of measure efficiency

identification oferosion hot spots

erosion control

consideration of actual practice and response of the watershed

long term reactionlanduse change

model requirementsrelevant aspects to be considered

Option

simulation of purification processes, short time consideration of pollution variability

identification of potential events

settling pondspre-dams

simulation of impact, evaluation of investment efficiency

significance ofpollution pointsources

sewage water treatment

simulation of measure efficiency

identification oferosion hot spots

erosion control

consideration of actual practice and response of the watershed

long term reactionlanduse change

model requirementsrelevant aspects to be considered

Option

Conclusions

Hydrology:•spatial rainfall distribution •interruption of flow due to transmission losses•sufficiently short time steps during flood events

Water quality: missing capabilities •Linkage of erosive nutrient leaching to rainfall distribution and run-off generation

•mass accumulation between significant floods

Conclusions

PescasPescas HSPFHSPFSWATSWAT Athys-PolTopmodel

Athys-PolTopmodel

europeanscale

large basins, long term simulation

Specialized land phase modelsmore detailedhydrology

distributed hydrological model

Interface: provision of time series for run-off/pollution from land phase

CascadeCascadePescasPescas stream network/pool module

stream network/pool module

european scale adapted routing detailed pool ecologyGW-interaction

Specialized network models:

processingsubdaily

information

processingsubdaily

information

spatial variability in run-off generation,

sediment delivery ratio

spatial variability in run-off generation,

sediment delivery ratio

Additional procedures:

the tempQsim tools

Conclusions


variable

technical soil conservationmeasures

rural development policyand land use management

operation of diversion structures, weirs,

flooding of sedimentation areas

operation of diversion structures, weirs,

flooding of sedimentation areas

Increased availability of safe water resources in main rivers and reservoirs

adapted consideration of highly hydrology and poullution dynamic

tempQsimtemptempQQsimsim

improved modelling tools

identification of controlable flow

intervals for diverting higher polluted flows

localisation of highest pollution sources, prioritise of actions

Improvedriver water quality

water quality dynamics in semiarid regions with temporary

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