MODELING SUSPENDED SEDIMENT TRANSPORT AND ASSESSING THE IMPACTS OF - - PowerPoint PPT Presentation

MODELING SUSPENDED SEDIMENT TRANSPORT AND ASSESSING THE IMPACTS OF CLIMATE CHANGE IN A KARSTIC MEDITERRANEAN WATERSHED

SOFIA NERANTZAKI TECHNICAL UNIVERSITY OF CRETE

Greek Speleological Society: Chania 1110 m below surface (1600 -490 m) Liontari sinkhole

Mediterranean features: Karstic Springs

Limitations: infrequency of intense rainfall, adverse field conditions

Data scarcity and flash floods

Koiliaris River Basin

• The permanent flow of the basin is supplied by the karstic springs of Stilos (mean

suspended sediment concentration: 4mg/L)

• Keramianos: a temporary tributary responsible for the flash flood events at the

hydrometric station H1 and for the majority of sediment mass transported at the basin exit

• Keramianos sub-basin: friable schist, invasive agricultural practices and
• vergrazing  the soil is erodible and easily transported

Dry Season First Flood H3 H2 H1

Koiliaris watershed

SedTrap – “CYBERSENSORS”

• Water stage and turbidity are recorded every five minutes.

Water stage is converted to flow with the use of a site specific rating curve.

• Flow proportionate sampling: interval between 20 and 80 m3/s is

divided into 6 volumetrically equal classes of 10 m3/s each; the pumping rate is augmented a class, every time the flow surpasses a class. Suspendent Sediment Node “Sediment Trap”. Consists of:

• 1x Control Unit “Libellium Waspmote”,
• 1x Radio Module (Zigbee),
• 1x Peristaltic Pump,
• 1x Stage Recorder
• 1x Turbidity Sensor.

Energy Independent.

+

Monitoring system

• Augmented version of the SWAT model: simulation of the contribution of the

extended karst to the spring discharge, accounting for the variability of the discharge recession due to two karst formations (Nikolaidis et al., 2013) Methodology

• The precipitation in the karstic area is directed to deep groundwater after

SWAT simulates surface hydrologic processes

• The deep groundwater flow from SWAT in the karstic area that could be

related to a specific spring is aggregated on a daily basis and becomes the input flow to a two part reservoir karst model Karst Model

Modified SWAT Model

• Input: Daily rainfall and temperature data 1973-2014, 5 meteorological stations
• Goodness of fit (daily records):
• NSE = 0.62 (> 0.5)
• PBIAS = 22.3% (< 25%)
• RSR = 0.62 (< 0.7)
• Annual average outflow of Koiliaris River Basin was estimated to be 621 mm/yr

(131 Mm3/yr)

Hydrology Simulation Two-part reservoir karst model

Suspended Sediment Concentration (SSC) Simulation

Concentration of mixed flow

Equations

• SSC simulation at (a) H1, (b) H3, (c) Stilos Springs
• 30% of the sediment yield of the extended karst sub-basins is driven into the

karst system through sinkholes

• During a flood event, the Keramianos tributary transports 95% of the sediment

mass  

1 1 1 in,1 in,1 1 1

d d V C a Q C Q C t      

   

2 2 1 in,1 in,1 2 1 1 2 2

d 1 d V C a Q C a Q C Q C t          

karst karst surface surf flow model karst surf flow

* * Q C Q C C Q Q   

• The input concentration Cin,1 is determined from the SWAT model, as a fraction of

the sediment yield from the HRUs which contribute to the karstic flow

SSC Modeling Results and Erosion

• (i) Keramianos (mean erosion rate):0.97 t/ha/yr.

(ii) Wet year: 1.6 t/ha/yr. (iii) Dry year: 0.55 t/ha/yr

• Keramianos mean sediment export is 3000 t/yr and

contributes 67% of the mean annual sediment export

• f the Koiliaris watershed (4500 t/yr).

On a wet year the sub-basin of Keramianos is responsible for the 63% of it and

• n a dry year Keramianos is responsible for the

70% of the total sediment export due to the high erodibility of its sub-basin.

Climate Scenarios

• Set of IPCC “A1B” climate change

scenarios: major decreases in surface flow (69.6%) and in the flow of the springs (76.5%) between the 2010-2049 and 2050-2090 time periods

• Sediment export is also decreasing

(54.5%)

Future Steps Input Uncertainty and Impact on Results

This section was implemented with the state scholarship IKY (SSF) funded by the Act "Strengthening the human research potential by implementing doctoral research" from funds of the OP "Human Resources Development, Education and Lifelong Learning" 2014-2020 co- financed by the European social Fund (ESF) and the Greek government

KARST SWAT

MONTE CARLO SIMULATION

Input Time Series - Stochastic Generation Quantification of Uncertainty for flow and sediment concentration

• utput

Cumulative distribution function of a random variable R showing the probability of any

• bserved value of R being less than or equal

to a given value r. Values generation from known probability distributions for precipitation and temperature. Deterministic simulation and the Monte-Carlo expected averages (and standard deviation) simulations for flow (the same stands for sediment concentration)

Thank you!