Environmental Engineering Reference
In-Depth Information
Box 22.1
Application of Source-Pathway-Receptor model to groundwater-induced flooding in the R´o
Salado Basin
Groundwater-induced waterlogging
Source
The primary source of this type of flood risk is groundwater in areas where the phreatic surface is
within 50-70 cm of the land surface.
Due to the relatively high infiltration capacity of the sandy soils that are prevalent in Region A
(Fig. 22.1b and Fig. 22.2) and the weak horizontal dynamics of the groundwater system, it may be
argued that the propensity for rainwater to infiltrate vertically and accumulate in the soils and so
increase the groundwater level constitutes a secondary source of this source of flood risk.
Pathway
This risk exists predominantly throughout the Northwest area of the basin (Region A), where a
delicate balance between rainfall and evapotranspiration - coupled with the geomorphological
characteristics of the area - maintains groundwater heads very close to the land surface.
Receptor
The main receptor of this flood hazard is agricultural activity, which is adversely affected through:
.
salinization of soils due to the rise of groundwater with a high salt content;
.
physical limitations on the growth of crops during the initial stage after sowing;
.
difficulty of accessing the land for harvesting.
Groundwater-induced surface flooding
Source
The primary source of this type of flood risk is water that exfiltrates in an area where the groundwater
table is at or above the land surface. This type of flooding also leads to ponding of rainwater during
precipitation events.
Pathway
This risk also exists throughout the Northwest area of the basin (Region A), where no surface water
drainage network has yet developed. Groundwater-induced surface flooding is common along inter-
dunal depressions. It appears first on the upstream side of parabolic dunes within the interdunal
depressions. Initially, the flooding so caused is not harmful. However, when the flood depth increases
sufficiently that water overtops the crests of the parabolic dunes, surface water cascades downstream
along the interdunal depressions, creating substantial volumes of surface runoff and forming a
significant pathway for this flooding mechanism.
Receptor
The receptors of this process are also the agricultural activities in the Northwest region. Losses occur
throughdisruptionof livestockactivities (unlikewaterlogging) andfarminfrastructure (suchas fences).
The occurrence of surface water flooding also implies crop damage. However, this is a relatively
small loss as cropping is not a major activity in these low-lying areas within the region.
Flooding mechanisms in the R´o Salado basin
yet adjusted to the current runoff regime. In fact,
the drainage system is formed by under-fit chan-
nels superimposed on relief formed by aeolian
(wind-blown)
Fluvial flooding occurs frequently in the R´o
Salado Basin because the drainage system has not
landforms
that
constrain the
