permaculture literature (Holzer 2010, 2011) as
well as recommended practices from regenerative
agriculture (popular literature, Gras 2012).
A ‘permaculture design’ including a series of
water reservoirs (Holzer 2011, p. 43; design,
p. 56; detailed section, p. 57) was created by an
architect and was subsequently implemented
with modifications. The intention was to reduce
stormwater soil erosion as well as to store harvested rainwater for groundwater recharge and to
create wildlife habitats. Bearing in mind the
context of continuing controversies over large
dams in particular (HLPE9 2015; Roy et al.
2011), the hope was to become more sustainable
in terms of independency from costly water
supplies piped from large artificial reservoirs in
Spain, e.g. the nearby Andévalo reservoir.
A series of four reservoirs were built (Fig. 1).
This was achieved either by simply digging a pit
with an excavator (reservoirs 1B, 2 and 3; Fig. 1)
and by combined pit digging and damming with
an earthen dike, taking into account existing
contour lines to keep water flow, geomorphology
and visual appearance as natural as possible
(reservoir 1A, Fig. 1). Typically, damming is
performed at a narrow section of a valley by first
excavating a core trench along the width of the
valley. The core trench cuts into the hills on both
sides and several meters below the future ground
of the reservoir to become an aquifuge. As an
impermeable barrier, the aquifuge should minimise seepage whilst impounding run-off water
from upstream catchments. According to Holzer
(2011), this ‘impermeable core’ should ideally be
connected to the existing natural layer of clay or
loam. The dam is subsequently built upwards by
filling the trench with the same locally sourced
material (clay/loam) which is compacted step-bystep either by a bulldozer or any compacting
machine (e.g., trench roller, drum roller or
vibratory rammer depending on the scale of the
building site). Building material must be neither
too dry nor too wet to ensure cohesiveness,
plasticity and compressive resistance of the soil
material (Röhlen and Ziegert 2014). Embankments on both sides of the dam may use soil
comprising 20–30% of clay according to Studer
and Liniger (2013) or any other soil material but
not humus according to Holzer (2011); dam
slopes should be no steeper than 1:2 (ibid., 69),
spillways for stormwater run-off must be installed on natural ground away from the dam (ibid.,
70) and the dam itself should be covered with a
high diversity of shallow rooting plants to prevent wind and water erosion of the structure;
deep rooting plants must be prevented from
growing their roots into the aquifuge to avoid
seepage. Trees like willows and alders may
support the structure if planted at the downstream
bottom of the dam, as described for a variety of
pond and lake constructions in Europe (Holzer
2011). Reservoirs 1A and 1B are interconnected
and allow any overflow from 1A to be stored in
1B, although interconnection disrupts the prereservoir natural drainage to the ephemeral south
of reservoir 1A (Fig. 1).
1.5 Specific Challenge and Research
Questions
Following the completion of reservoir 1A by the
end of 2010 and remaining reservoirs 1B, 2 and 3
by the end of 2013, all reservoirs do catch water
after rainfall events or rainfall on already saturated soil, but so far the reservoirs have only
filled up to a fraction of their total capacity.
Reservoirs 1B and 3 have failed to retain water
beyond a few months and never retained water
throughout the year. Although reservoirs 1A and
2 are constantly supplied with some water, this is
only partly due to rainfall and mainly related to
irrigation system maintenance. The required filters against particulate matter need to be flushed
regularly by reversing flow direction. This rinsing water is then pumped into the respective
reservoir for disposal several times a day (farm
manager personal communication). The present
research is aimed at indicating the root causes of
potential performance limits of these reservoirs,
in view of a considerable financial investment for
land use conversion and reservoir construction.
Usefulness of Surface Water Retention Reservoirs …
61
well as recommended practices from regenerative
agriculture (popular literature, Gras 2012).
A ‘permaculture design’ including a series of
water reservoirs (Holzer 2011, p. 43; design,
p. 56; detailed section, p. 57) was created by an
architect and was subsequently implemented
with modifications. The intention was to reduce
stormwater soil erosion as well as to store harvested rainwater for groundwater recharge and to
create wildlife habitats. Bearing in mind the
context of continuing controversies over large
dams in particular (HLPE9 2015; Roy et al.
2011), the hope was to become more sustainable
in terms of independency from costly water
supplies piped from large artificial reservoirs in
Spain, e.g. the nearby Andévalo reservoir.
A series of four reservoirs were built (Fig. 1).
This was achieved either by simply digging a pit
with an excavator (reservoirs 1B, 2 and 3; Fig. 1)
and by combined pit digging and damming with
an earthen dike, taking into account existing
contour lines to keep water flow, geomorphology
and visual appearance as natural as possible
(reservoir 1A, Fig. 1). Typically, damming is
performed at a narrow section of a valley by first
excavating a core trench along the width of the
valley. The core trench cuts into the hills on both
sides and several meters below the future ground
of the reservoir to become an aquifuge. As an
impermeable barrier, the aquifuge should minimise seepage whilst impounding run-off water
from upstream catchments. According to Holzer
(2011), this ‘impermeable core’ should ideally be
connected to the existing natural layer of clay or
loam. The dam is subsequently built upwards by
filling the trench with the same locally sourced
material (clay/loam) which is compacted step-bystep either by a bulldozer or any compacting
machine (e.g., trench roller, drum roller or
vibratory rammer depending on the scale of the
building site). Building material must be neither
too dry nor too wet to ensure cohesiveness,
plasticity and compressive resistance of the soil
material (Röhlen and Ziegert 2014). Embankments on both sides of the dam may use soil
comprising 20–30% of clay according to Studer
and Liniger (2013) or any other soil material but
not humus according to Holzer (2011); dam
slopes should be no steeper than 1:2 (ibid., 69),
spillways for stormwater run-off must be installed on natural ground away from the dam (ibid.,
70) and the dam itself should be covered with a
high diversity of shallow rooting plants to prevent wind and water erosion of the structure;
deep rooting plants must be prevented from
growing their roots into the aquifuge to avoid
seepage. Trees like willows and alders may
support the structure if planted at the downstream
bottom of the dam, as described for a variety of
pond and lake constructions in Europe (Holzer
2011). Reservoirs 1A and 1B are interconnected
and allow any overflow from 1A to be stored in
1B, although interconnection disrupts the prereservoir natural drainage to the ephemeral south
of reservoir 1A (Fig. 1).
1.5 Specific Challenge and Research
Questions
Following the completion of reservoir 1A by the
end of 2010 and remaining reservoirs 1B, 2 and 3
by the end of 2013, all reservoirs do catch water
after rainfall events or rainfall on already saturated soil, but so far the reservoirs have only
filled up to a fraction of their total capacity.
Reservoirs 1B and 3 have failed to retain water
beyond a few months and never retained water
throughout the year. Although reservoirs 1A and
2 are constantly supplied with some water, this is
only partly due to rainfall and mainly related to
irrigation system maintenance. The required filters against particulate matter need to be flushed
regularly by reversing flow direction. This rinsing water is then pumped into the respective
reservoir for disposal several times a day (farm
manager personal communication). The present
research is aimed at indicating the root causes of
potential performance limits of these reservoirs,
in view of a considerable financial investment for
land use conversion and reservoir construction.
Usefulness of Surface Water Retention Reservoirs …
61