Ourania Tzoraki

Water and sediment transport modeling of a large temporary river basin in Greece

The objective of this research was to study the spatial distribution of runoff and sediment transport in a large Mediterranean watershed (Evrotas River Basin) consisting of temporary flow tributaries and high mountain areas and springs by focusing on the collection and use of a variety of data to constrain the model parameters and characterize hydrologic and geophysical processes at various scales. Both monthly and daily discharge data (2004-2011) and monthly sediment concentration data (2010-2011) from an extended monitoring network of 8 sites were used to calibrate and validate the Soil and Water Assessment Tool (SWAT) model. In addition flow desiccation maps showing wet and dry aquatic states obtained during a dry year were used to calibrate the simulation of low flows. Annual measurements of sediment accumulation in two reaches were used to further calibrate the sediment simulation. Model simulation of hydrology and sediment transport was in good agreement with field observations as indicated by a variety of statistical measures used to evaluate the goodness of fit. A water balance was constructed using a 12 year long (2000-2011) simulation. The average precipitation of the basin for this period was estimated to be 903 mm yr(-1). The actual evapotranspiration was 46.9% (424 mm yr(-1)), and the total water yield was 13.4% (121 mm yr(-1)). The remaining 33.4% (302 mm yr(-1)) was the amount of water that was lost through the deep groundwater of Taygetos and Parnonas Mountains to areas outside the watershed and for drinking water demands (6.3%). The results suggest that the catchment has on average significant water surplus to cover drinking water and irrigation demands. However, the situation is different during the dry years, where the majority of the reaches (85% of the river network are perennial and temporary) completely dry up as a result of the limited rainfall and the substantial water abstraction for irrigation purposes. There is a large variability in the sediment yield within the catchment with the highest annual sediment yield (3.5 t ha(-1)yr(-1)) to be generated from the western part of the watershed. The developed methodology facilitated the simulation of hydrology and sediment transport of the catchment providing consistent results and suggesting its usefulness as a tool for temporary rivers management.

Flood generation and classification of a semi-arid intermittent flow watershed: Evrotas river

Hourly water level measurements were used to investigate the flood characteristics of a semi-arid river in Greece, the Evrotas. Flood events are analysed with respect to flood magnitude and occurrence and the performance of Curve Number approach over a period of 2007–2011. A distributed model, Soil and Water Assessment Tool, is used to simulate the historic floods (1970–2010) from the available rainfall data, and the performance of the model assessed. A new flood classification method was suggested the Peaks-Duration Over Threshold method that defines three flood types: ‘usual’, ‘ecological’ and ‘hazardous’. We classify the basin according to the flood type for the most serious past simulated flood events. The proportion of hazardous floods in the main stream is estimated to be 5–7% with a lower figure in tributaries. Flood Status Frequency Graphs and radar plots are used to show the seasonality of simulated floods. In the Evrotas, the seasonality pattern of hazardous flood is in agreement with other studies in Greece and differs from other major European floods. The classification in terms of flood types in combination with flood type seasonality is identified as an important tool in flood management and restoration.

Hydrologic modelling of a complex hydrogeologic basin: Evrotas River Basin

Climate change is expected to affect mostly water resources in arid and semi-arid areas, imposing in this way significant constraints in satisfying water demands in these regions. Under these conditions, water resources management should focus in increasing the efficiency of water uses by minimizing water losses and improving on the water balance accounting of the watersheds. Evrotas River Basin is a typical case of a water resource that has been under intense human pressure due to extensive water abstractions. Pumping from numerous wells (approximately 3000 private wells) and surface water abstractions impose significant uncertainty in water balance estimation and a new approach was developed to constrain the system and improve on the water balance assessment. The ETD (Enhanced Trickle Down model), a physically-based watershed model was coupled to a karstic model and were used to simulate the hydrologic response of the watershed. Ten years of data were used to simulate the hydrologic regime of the watershed. Losses from the karst due to evapotranspiration and infiltration to the deeper aquifer were estimated to be 45% of its annual volume. Karst is recharged annually by a water volume of 306Mm³ and only 24% (75Mm³) recharges the river as karst baseflow. The annual rainfall volume (for the non-karstic area of the watershed) was estimated to be 629Mm³, the evapotranspiration was 655Mm³, stream discharge 152Mm³ and stream abstraction and irrigation were 77Mm³. On the average, the amount of irrigation (77Mm³) corresponded to 900 mm (per year for agricultural areas) which is almost twice the recommended irrigation levels. The modelling approach presented in this work can be used to constrain the uncertainty in the hydrologic budget of basins with complex hydrogeomorphology.

Attenuation capacity of a coastal aquifer under managed recharge by reclaimed wastewater

Managed Aquifer Recharge (MAR) is becoming an increasingly attractive water management option, especially in semiarid areas. Nevertheless, field studies on the fate and transport of priority substances, heavy metals and pharmaceutical products within the recharged aquifer are rare. Based on the above, the objective of this project is to study the hydrological conditions of the coastal aquifer of Ezousa (Cyprus) and its ability to attenuate pollutants. The Ezousa riverbed is a locally important aquifer used for a MAR project where treated effluent from the Paphos Waste Water Treatment Plant is recharged into the aquifer through a number of artificial ponds along the riverbed. Additionally, groundwater is pumped for irrigation purposes from wells located nearby. The hydrological conditions of the area are unique due to the construction of the Kannaviou dam in 2005 that reduced natural recharge of the Ezousa aquifer significantly, inducing the saltwater intrusion phenomenon. A three-dimensional finite element model of the area was constructed using the FEFLOW software to simulate the groundwater flow conditions and transport of Phosphorous and cooper in the subsurface from the recharge process. The model was calibrated using hydraulic head and chemical data for the time period of 2002-2011. The groundwater model was coupled with a geochemical model PHREEQC attempting to evaluate nitrate and Copper processes. Inverse modeling calculation was used to determine sets of moles transfers of phases that are attributed to the water composition change in groundwater between the mixture of natural groundwater and reclaimed wastewater and the final water composition.

Hydrograph analysis of Inountas River Basin (Lakonia, Greece)

Three approaches have been used to analyze the hydrograph of Inountas River basin in two reaches. Flow in each reach was estimated by combining the water level records with monthly field flow measurements. Base-flow separation has been accomplished by using the SWAT (Soil and Water Assessment Tool) baseflow filter program. The fraction of water yield contributed by baseflow was estimated between 0.76-0.62 for Kladas reach and 0.79-0.70 for Vassaras reach respectively. Flow duration curve for each reach was constructed from daily flow data. The flow-probability relationship, Q50 for Vassaras reach had a value of 0.164 and for Kladas 0.198. The ratio Q90/Q50 for Vassaras reach was 0.689 indicating that 68.9% of Vassaras stream flow was contributed from groundwater storage. The calculated recession factors were for Kladas reach 0.024 (10/04/2010- 04/06/2010) and for Vassaras reach 0.009 (20/03/2010-27/05/2010) and 0.005 (09/07/2010-11/10/2010).

Delineating hydrological response units in a mountainous catchment and its evaluation on water mass balance and model performance

Semi-distributed physically-based models are well established and widely used for hydrological modeling due to their ability to capture the spatial variability of the watershed among land use, soil types and topographic characteristics; and to characterize distributed inputs in different areas within the watershed. They offer a more realistic watershed representation, allowing for better predictions of the behavior of a hydrologic system, based on novel climatic inputs. Watershed subdivision and the question of an optimum discretization level is an important issue in distributed hydrological modeling as it affects the setup of hydrologic models and has the potential to affect model output. Soil and Water Assessment Tool (SWAT), a semi-distributed physically-based hydrologic model, divides the watershed into smaller subwatersheds which are further subdivided into HRUs consisting of homogeneous land use, soil, slope and management characteristics. The number and size of HRUs is calculated based on user-specified land use, soil and slope thresholds. This study investigates the impact of the slope threshold in the HRU definition on flow predictions and hydrologic mass balance, applied on three subwatersheds of the Evrotas River Basin (1348km2), a mountainous catchment in Peloponnesus, Greece. The catchment is delineated using a 90m DEM and then divided into 150 subwatersheds. The model was calibrated, and simulations were performed on three subwatersheds using a range of 5%- 30% slope thresholds for the HRU definition while land use and soil thresholds remained the same. Results showed that the coarser delineation (13 HRUs) produced a very accurate hydrologic mass balance and satisfactory flow predictions (RSR, PBIAS, NSE) while, finer delineations (21 HRUs) produces inaccurate hydrologic mass balance (54.49% lower surface runoff) but more accurate flow predictions (RSR, PBIAS, NSE).

Simulation of daily discharge using the distributed model SWAT as a catchment management tool-Limnatis River case study

The Soil and Water Assessment Tool (SWAT) was evaluated while modeling daily stream flow in Limnatis basin, Cyprus over a period of seven years. Stream flow data from 2006-2008 were used as a warm up period, the period 2008- 2010 was used to calibrate the model and stream flow, data from 2008-2012 were used for the validation. The model could adequately predict daily stream flow trends with Nash-Sutcliffe values of 0.68. Overall the results of the simulation indicate that SWAT model can be an effective tool for the modeling of stream flow in intermittent rivers like Limnatis, and could contribute valuable information for successful catchment management.

Assessing the efficiency of a coastal Managed Aquifer Recharge (MAR) system in Cyprus

Managed Aquifer Recharge (MAR) is becoming an attractive water management option, with more than 223 sites operating in European countries. The quality of the produced water, available for drinking or irrigation processes is strongly depended on the aquifers hydrogeochemical characteristics and on the MAR system design and operation. The objective of this project is the assessment of the operation efficiency of a MAR system in Cyprus. The coupling of alternative methodologies is used such as water quality monitoring, micro-scale sediment sorption experiments, simulation of groundwater flow and phosphate and copper transport in the subsurface using the FEFLOW model and evaluation of the observed change in the chemical composition of water due to mixing using the geochemical model PHREEQC. The above methodology is tested in the Ezousa MAR project in Cyprus, where treated effluent from the Paphos Waste Water Treatment Plant, is recharged into the aquifer through five sets of artificial ponds along the riverbed. Additionally, groundwater is pumped for irrigation purposes from wells located nearby. A slight attenuation of nutrients is observed, whereas copper in groundwater is overcoming the EPA standards. The FEFLOW simulations reveal no effective mixing in some intermediate infiltration ponds, which is validated by the inverse modeling simulation of the PHREEQC model. Based on the results, better control of the infiltration capacity of some of the ponds and increased travel times are some suggestions that could improve the efficiency of the system.

Resilience of Touristic Island Beaches Under Sea Level Rise: A Methodological Framework

ABSTRACT This contribution addresses the need for a simple model for managers to employ when planning strategies for the management of touristic beaches under sea level rise. A methodological framework was developed and tested in two Aegean archipelago islands (Lesvos and Rhodes, Greece). The scheme can represent the status of touristic island beaches, based on easily obtained variables/indicators and projections of beach erosion/retreat under different scenarios of mean sea level rise (MSLR) and extreme events. Information on beach geomorphological characteristics, environmental setting, water quality, management, and services (such as those used in the “Blue Flag” classification) was collated/collected and beach erosion/retreat due to CV & C was estimated through suitable ensembles of cross-shore (1-D) morphodynamic models. A Strength-Weaknesses-Opportunities-Threats (SWOT) framework was employed to assist in the selection of indicators and multicriteria analysis used to optimize indicator weights and rank beaches according to their sustainability under sea level rise. Implementation of the framework at the two islands has shown that: the majority of Lesvos and Rhodes beaches (82% of a total of 217 beaches and 58% of a total of 97 beaches, respectively) can be classified as beaches with no, or minimal, human interference, suggesting that under environmentally sound coastal management further touristic development might be afforded; there could be very significant effects of the sea level rise on the carrying and buffering capacities of the most developed (“Blue Flag”) beaches, with some expected even under conservative projections to be completely eroded by 2100, unless technical adaptation measures are taken; and using the proposed framework, touristic beaches can be rapidly ranked in terms of their resilience to sea level rise and their development potential, allowing prioritization of effective management responses.

Nutrient dynamics management based on GIS modeling tools

Nutrient sources and fate are investigated in the Evrotas, a temporary river in Greece. We assess field monitoring and modelling tools for the estimation of nutrient fate and transport through various diffuse pathways. The ‘total daily maximum load’ approach is used to estimate the nutrient flux status by flow class and measures are recommended and applied for each flow status. Using this approach in Evrotas basin, it was estimated that almost 60% of the river network fails to meet nitrogen criteria and 50% phosphate criteria. We recommend that existing well-documented remediation measures such as reforestation of the riparian area should be implemented to achieve load reduction in close conjunction with social needs.