MONITORING SEDIMENT TRANSPORTDURING FLOODS IN TUSCANY

Francalanci Simona 1, Paris Enio 2, Solari Luca 2, Minatti Lorenzo 1, Giorgio Valentino Federici 2

1 CERAFRI – Center of Research and Advanced Education for Hydrogeological Risk Prevention, Via XI Febbraio 2, 55040 Retignano di Stazzema (LU), Italy.2 Department of Civil and Environmental Engineering, University of Florence, Via S.Marta 3, 50139 Firenze (FI), Italy.

Severe coastal erosion is affecting the Region of Tuscany (Central Italy) since the middle of last century. In order to plan and design the mitigation measures, the Regional Administration has funded a project aimed to assess both the quantity and quality of sediment delivery to the sea.

Since 2006 four sediment transport monitoring stations have been installed in the north-western part of Tuscany

Monitored stations

N..

of

events

Drainage area

at the station

[km2]

Totalbasin area

[km2]

D50 at the station

[mm]

Versilia 12 96 106 29.0

Magra 6 524 1698 49.5

Serchio 16 1355 1565 33.0

Arno 9 4083 8186 30.8

TUSCANY

Italy

THE MONITORING STATIONS

AIMS: - develop flow-sediment rating curves for the monitoring stations;- Investigate similarity laws of sediment transport in the Tuscany river basins.

Florence Rosano

F. ArnoF. Arno

Tirr

eno

Sea

A = 4083 Km 2

gauging station

ARNO RIVER MONITORING STATION

Sample verticals

Arno gauging station

Rosano bridge

SERCHIO RIVER MONITORING STATION

VERSILIA RIVER MONITORING STATION

MAGRA RIVER MONITORING STATION

FIELD PHASE Instruments are controlled from bridge

by a mobile crane and by a cable-and-reel system

THE METHODOLOGY TO DEVELOP

THE SEDIMENT RATING CURVE

Rating curve: a combined approach (*)Field phase

Bed material sampling - Hydrometric data - samples of sediment transport during s flood events

Modeling phaseCompute flow and sediment discharge

from field measurements – Modeling flood events and sediment transport dynamics - Development of sediment rating curves

Laboratory phaseGrain size distribution of bed material - bedload samples

and concentration of the suspended sediments

(*)

RATING CURVEComparisons of experimental data with existing sediment transport equations (Parker, 1990; Powell

Reid & Laronne, 2001; Wilcock & Crowe, 2003; Smith & Mc-Lean, 1977; Van Rijn, 1984) have been carried out.

In terms of total load the equation of Ackers & White (1973) in the modified version by White & Day (1982) has proved to be reliable.

Trasporto solido totale

0.0100

0.1000

1.0000

10.0000

100.0000

1000.0000

100 1000Portata liquida (m3/s)

Porta

ta so

lida

(Kg/

s)

MISURE

Ackers eWhite mod.

Trasporto solido totale

0.0100

0.1000

1.0000

10.0000

100.0000

1000.0000

100 1000Portata liquida (m3/s)

Porta

ta so

lida

(Kg/

s)

MISURE

Ackers eWhite mod.

Serchio River- sediment rating curve

measureddata

Q [m3/s]

Q s [

Kg/

s]

COMPARISON OF RATING CURVESconsidering the whole set of data

the plot of the total sediment load Qs [Kg/s] vs. liquid discharge Q [m3/s] seems to suggest a similar behaviour between rating curves

 

SEDIMENT RATING CURVE IN TERMS OF DIMENSIONLESS VARIABLES

CONCLUSIONS

Despite the large difference in the drainage areas (from 96 km2 to 4083 km2) and bed sediment sizes (D50 from 29 mm to 50 mm), results show the rating curves (total sediment discharge vs. flow discharge) made dimensionless with appropriate scaling factors overlap, thus suggesting the existence of common scaling laws.

The common scaling laws can be used to extend the flow –sediment relationships from monitored to non-monitored rivers.

Prediction of total sediment transport in the Tuscany basins by using a “unique” (or regional) sediment rating curve is under investigation

Thank you for your attention!