CNR-IRSA activities related to INHABIT

The hydrology of riparian zones

In order to study the role of riparian zones in the removal of nitrogen it is crucial knowing the dynamic of groundwater at both general and local level. The measurements of the hydraulic head and hydraulic conductivity are essential to determine the velocity and the direction of the groundwater flow in the different horizons. Furthermore, it is important to know the width and location of the more permeable soil layers in order to identify the more relevant processes involved in the nutrient turn over.In the aquifers the water pressed by the gravity, moves along flow lines that, in the superficial portion,  follow the profile of the soil surface. The measure of the hydraulic head in piezometers located at different depth in the study areas, permit to trace the equipotential lines (lines of constant head) and obtain a  flow net of a specific riparian area.

Figure Example of equipotential lines measured in the riparian zone of the Fontanin spring (NO) (Cross section); The arrows indicate the direction of the groundwater flux.

The hydraulic conductivity (Ksat), i.e., the soil ability in coveying water, is a key parameter in order to study the water transport and the nutrient retention in riparian areas. There are several methods to measure the Ksat and, when the soil profile is very simple and uniform with distinct horizons, it is possible to use the conductivity values available in the literature. Alternatively a reasonably estimate of the hydraulic conductivity is obtained by the “slug test” or “emptying or filling test” making use of  the piezometers installed in the study area. The slug test consists in producing an immediate variation of the water level inside a piezometer or a well in order to measure the recovery of the original level as a function of the time. Several mathematical methods allow to calculate the Ksat using the data from the slug test. The choice of the method depends both on the aquifer features (e.g. confined, semi-confined or free) and on the piezometer position within the aquifer. When the piezometer are partially introduced in the aquifer but they do not reach the base it is possible to use the Bower&Rice  method (Fetter, 2001).