Soil loss modeling and Forest landscape management perspectives Sihem Jebari National Research Institute for Rural Engineering, Water and Forestry AGORA Project Hammamet 30 th Sept. 3 rd Oct. 2010
CONTENTS 1- Introduction (Landscape degradation) 2- Water erosion- Tunisia 3- Objectives 4- Study area 5- Methodology 6- Expected results 7- Conclusion and perspectives
Views across the semiarid agricultural landscape.
The historical background of the agricultural landscape management all over 3000 years contributed to give specific shapes of land occupation, and natural resources exploitation. active erosion processes Numid (1500 B.C.) Punic (1000 B.C.- 146 B.C.) Arab (700 A.C. 1500 A.C.) Roman (146 B.C. 600 A.C.) Ottoman (1500 A.C. 1880 A.C.) Colonial (1880 A.C. 1956 A.C.) Modern (1956 A.C. 2010 A.C.)
The Siliana and Mellegue woods were rich in pines, highly appreciated for boat building since it creates light ships. Wood was among the most valuable goods in the Mediterranean Sea trade circle. The Carthagian carpenters assembled and put afloat boats on an average of one vessel each 2 days.
Carthage 1 32 The nearest pine-forest to Carthage via Mejerda was that of Siliana, which underwent an even stronger pressure than the farther located Mellegue forest.
Water erosion -Tunisia Dorsal catchments offered since old times, good shelter, rich grazing, fertile soils, fabulous crop yield and commercial prosperity to its population Deforestation water erosion (wood trade + farming on sloping land) Rural and agricultural degradation landscape
Recent research has shown that the semiarid areas are very vulnerable to water erosion phenomenon Increases area of the arid belt (e.g., south of the Maghreb) Affects 20% of the total land area (yearly, 15000 ha are lost) Silts reservoirs (40 million m 3 /year)
Consequences of water erosion phenomena Declining of fertility Reservoir siltation Water pollution Unstable flows of rivers Spreading of badlands Desertification progress
OBJECTIVES The aim of this study is to contribute in suggesting sustainable strategies in managing natural resources. To determine the impact of the forest in preventing water erosion phenomenon and sediment yield To predict soil loss distribution at the scale of a catchments To suggest the most suitable area for forest settlement in order to limit landscape degradation.
Studied area The Dorsal mountains represent the last part of the Atlasic mountain ranges towards the east. Seven (7) % of the area are badly damaged by erosion and 70% of the area are moderately damaged. It plays an important role in the hydrology since it links the main wadis. It coincides with 400 mm/year isohyete. At present only 28% of the dorsal soil cover is left
Observed Network -28 experimental catchments along the Tunisian Dorsal range - Automatic rain gauge network was set up by the EU-funded Program HYDROMED (Research program on hill reservoirs in the semiarid Mediterranean periphery,1992 2002; SERST- IRD-DGACTA, 2000).
- Each catchment discharges into a small dam, where bathymetric measurements have been undertaken according to echo-sounding procedure. - Siltation data for the reservoirs are available from annually published hydrological reports (DCES/IRD, 1994-2002).
Methodology To analyse rainfall data (temporal distribution, max. Intensities, return period etc.) using Matlab software To define the most active erosion process in forest areas To prepare various USLE model thematic maps (ARC-view) - Discretizing the studied area into small regular grid cells with the GIS tool
- USLE/GIS approach + multi-criteria analysis Calibration soil loss rate
Universal Soil Loss Equation (USLE) The USLE equation is used to determine mean annual soil loss A (t/ha/yr) as a function of six erosion factors: A = R K L S C P where R is rainfall erosivity factor (m t/ha h), K (t ha/m t) is soil erodibility factor, L is length factor (m), S is slope factor (%), C is crop management factor (unit-less) and P a conservation practice factor (unit-less).
EXPECTED RESULTS -Establish relationship between forest area and soil erosion rate within the catchments - Determine the spatial distribution of soil loss rates within the studied areas - Compare between observed and generated soil loss distribution -Suggest a forest settlement in order to prevent landscape degradation and reservoir siltation
CONCLUSION AND PERSPECTIVES To better conserve and manage forest domains where water erosion is active Scientists & Rural engineers Suitable management scenarios at watershed scale
- Spatial soil loss rates can be used as a management tool for water and soil conservation strategy - Promote balanced land settlements over the anthropized catchments - Soil loss estimation should be tested for other experimental watersheds