SALINIZATION RISK ASSESSMENT IN IRRIGATED ALLUVIUM AREAS OF SEMI-ARID REGIONS
S
UZANA M.G.L. MONTENEGRO
Departamento de Engenharia Civil- UFPE, Cidade Universitária, Recife, PE.
Presented by ALCIDES N. SIAL
Soil and groundwater salinization occurs mainly in arid and semi-arid regions. It may arise due to climate conditions, but is more prevalent where irrigation practices alter the natural salt balance. Irrigation can promote salinization by raising the water table of the underlying aquifer, carrying salts upwards either from saline groundwater or from soil profile. Salts, unlike water, remain in the soil as soil evaporation and plant transpiration take place. Salts accumulated in the soil can also be moved downwards through irrigation or groundwater fluctuations, and eventually penetrate the aquifer, thereby reinforcing the salinity problem.
Control of salinisation is a key factor for sustainable irrigated agriculture, in which maximum crop yield is desirable at the same time as natural resources are preserved. Irrigation management proposals, aiming salinity control, depend upon assessment of salinity levels. Mathematical models provide the means for predicting the behavior of physical systems, and thus may be applied to design and management studies considering different scenarios of water use and quality.
Heterogeneity of the soil hydraulic properties and their associated measurement errors constitute the major sources of uncertainties in modeling the movement of water and solutes (salts) in field soils. Consideration of these uncertainties in a stochastic modeling framework leads to the possibility of quantifying the uncertainty in the model's output variables, which are in turn basic information for salinity risk assessment and proposal of management strategies.
Existing methodologies and mathematical models have been combined and adapted to develop an useful tool for salinity risk assessment in shallow groundwater systems, accounting for spatial variability and measurement errors associated with the soil hydraulic properties.
A case study is presented, based on a small- scale irrigation project in the Northeast of Brazil. The importance of this system is related to its general characteristics which make it a paradigm for a large number of similar ones in the region. Groundwater quality and quantity in the system have been monitored for the last four years. Evidences of degradation by salinization can already be noticed. Stochastic analysis is performed to show examples of the impact of different scenarios of irrigation water quantity and quality on plant yield. (May 19, 2000)
Publication Dates
-
Publication in this collection
05 Jan 2001 -
Date of issue
Dec 2000
