Study of the hydrology in the Candelaro catchment using a semi-distributed model

1. Study of the hydrology in the Candelaro catchment using a semi-distributed model G. Santese, AM De Girolamo, A. Lo Porto Water Research Institute IRSA - CNR

2. Case study: the Candelaro River

3. Basin description • Catchment located in Puglia in the second largest Italian plain "Tavoliere di Puglia" • Province: Foggia • Municipalities: 24 • Total number of inhabitant: about 347.000 • Size: about 2300 km² • Larger tributaries: Triolo, Salsola, Vulgano and Celone • S.Vincenzo reservoir • Main economic activity: agriculture

4. Main problems • Area under high risk of desertification • Intensive irrigated horticulture • Frequent floods (causing deaths and big damages to properties and structures) • Natural flow not respected • Downstream wetlands (natural reserves, Ramsar sites, Gargano National Park) • Elongated time of water scarcity • Poor in-stream water quality

5. River characteristics In the upper part • Good natural status, • One dam in the Celone subbasin • Three designed dams and weirs in the Salsola, Vulgano and Triolo subbasins In the lower part and tributaries • Highly anthropic • Sections are modified • Lined channel • In the most downstream part • Complex hydraulic situation due to the presence of a lateral ditch

6. Annual precipitation: • 700 - 1000 mm in the western and eastern part • 400 - 700 mm in the middle part (lowland) Average annual runoff: 160 mm Land use: 14% forest / grazing, 2% urban, 84% agriculture Representatives crops: Winter wheat - corn - tomato - sugar beet - potato - lettuce - olive tree - grapevine

7. Main conflicting interests Water shortage for satisfaying all the uses vs overexploitation of groundwater for irrigation, bringing to a progressive impoverishment of the aquifer reservoirs and, in several zones, to a total absence of shallow groundwater; Rainfall rates decrease of about 30% during the last 40 years vs a radical change in the agricoltural practices from an extensive grain farming to a highly water demanding horticultural farming; Intensive horticultural farming vs surface and groundwater quality and quantitative

8. Water quantity and quality Surface water quantity: low flow often joined to municipal waste water discharge and/or uncontrolled discharges; quality: high levels of N-NO3, TOC, COD, N-Org, N-NH3 due to sewer pollution and agriculture massive use of manure, herbicide and fertilizers. However no anoxic and/or acidity phenomenon are observed. Groundwater quantity: extensive and sensible decrease of piezometric surface causing, in some case, the abandonment of wells. quality: high antropic pressure with compromised/bad hydro-chemical characteristics tied almost always to the elevated concentration of nitrates and salts, specially Cl and Na. Not suitable to drinkable use and, in much case, to irrigated use too.

12. Application of the SWAT model to the Celone subcatchment

13. EROSIONE (t/ha)

14. EROSIONE (t)

17. SEDIMENTI

18. SEDIMENTI (carico)

20. WATER BALANCE(mm) 150 mm 100 mm

21. SOME DATA ON WATER BALANCE IN THE PLAIN Surface w.wheat/tomato 11,000 ha Groundwater recharge 8,243,000 m3 Irrigation (from groundwater) 35,000,000 m3 Recharge / withdrawal % ratio 25 % Annual deficit 26,757,000 m3 Perfect agreement with measured data Groundwater depression 1 m / 4 years

22. 1990 1991 1992 1993 1994 1995 1996 Daily flow measures

23. Subdaily flow measures (2 hours)

27. Flashiness index

28. Preliminary results of the application of the SWAT model to the CANDELARO catchment

29. The Candelaro basin Inlet water discharge Flow Gauges: San Severo San Vincenzo

30. Sandy clay loam Clay loam Sandy clay loam Silty clay loam Sandy clay loam Clay Clay Clay loam Sandy clay loam Clay Clay loam Clay loam Loam Silty clay loam Sandy loam Sandy loam Clay loam Loam Clay loam Silty clay loam • Soil Map

31. Landuse

32. MULTIPLE HRUs Landuse/Soil THRESHOLDS: 5/15 [%] Number of Subbasins: 34 Number of HRU: 195 • HRU Distribution

33. Irrigation 204.5 Mm3/yr Rc = 0.29 WWTP discharge 22.1 Mm3/yr Rainfall 1031.9 Mm3/yr Modeled Water balance

34. Modeled Water balance

35. CONFRONTO TRA VALORI MISURATI E CALCOLATI

36. Simulated Water Flow

37. DREAMS Distributed model for Runoff, Evapotranspiration, and Antecedent soil Moisture simulation A semi-distributed hydrological model, suitable for continuous simulations, based upon the use of daily and hourly time steps. It includes a daily water budget and an “event scale” hourly rainfall-runoff module. The two modules may be used separately or in cascade for continuous simulation. The main advantages of this approach lay in the robust and physically based parameterization. (S. Manfreda, M. Fiorentino, and V. Iacobellis, Advances in Geosciences, 2, 31–39, 2005)

38. DREAMS In-coming and out-going fluxes in a single grid-cell. The cell represents the control volume of the water balance equation.

39. DREAMS • Canopy cover determines the amount of rainfall intercepted by vegetation before hitting the soil surface. ( f (LAI, NDVI)) • Throughfall (precipitation minus interception) is initially stored in surface depressions. • Net precipitation (throughfall minus depression storage) is then subdivided in infiltration into the soil and surface runoff (infiltration excess). • Soil water content is redistributed within river sub-basins according to the morphological structure of the basin. (Wetness Index) • Groundwater recharge is obtained as cell percolation through the vadose zone and is routed as a global linear reservoir (as a function of the hydraulic conductivity of soil, Eagleson, 1978). • Basin’s daily streamflow is found as the sum of runoff, including exfiltration from subsurface redistribution and groundwater flow produced by a conceptual reservoir. • When daily rainfall exceeds a threshold s the H-DREAM module (running at hourly scale) is activated and runoff is routed through the basin in order to obtain the flow hydrograph.

40. Wetness Index (Beven & Kirkby, 1979)

41. Wetness Index (Beven & Kirkby, 1979) Wi = ln(a/tanβ) Where Wi = wetness index a = drainage area per unit contour length tan β = is the local slope in the steepest descent direction

42. The End