Environmental Engineering Reference
In-Depth Information
Box 4.2 Repairing landscape processes: ponding water in rangelands
Around the world, there are rangelands that have been
damaged by grazing so that wind and water erosion
have removed vast areas of topsoil to expose hard
clay subsoils (Figure 4.4a). These landscapes are
typically fl at and barren, and are called scalds, hard-
pans, clay pans or blowouts. Such scalds have very
low water infi ltration rates so that during and after
rainfall events most of the water runs off and is lost
from the landscape. Repairing water retention proc-
esses (infi ltration and run-on) in these scalded land-
scapes presents restorationists with signifi cant
challenges (Whisenant 1990), primarily because water
runs off the land so rapidly that erosion continues to
occur and very little vegetation establishes even if
grazing ceases.
However, a team of restorationists in semi-arid
south-eastern Australia has taken on this challenge,
and has designed and implemented a restoration tech-
nology known as water ponding (Thompson 2008).
Their goal was to bring scalds back to productivity.
Their analysis of scalded landscapes suggested that
the main problem was water retention. Using laser-
levelling and machinery, they built low earthen banks
along contours to form 'ponds' (Figure 4.4b). These
ponds function to retain water for a much longer
period after rainfall events. They found that water
ponding was very effective when scalded soils had
swell-shrink properties, which caused them to swell
slightly when wet but then shrink as they dried out.
This process forms a network of cracks, which facili-
tates improved water infi ltration in subsequent rainfall
events. The cracks also trap seeds and other organic
debris. Vegetation then establishes, triggering growth
pulses that improve soil properties as the concentra-
tion of organic matter in the soil increases. Water-
ponding technology was less effective on scalds
having soils with weak swell-shrink properties.
This team has constructed more than 50 000 water
ponds on scalded areas in the Marra Creek district of
New South Wales, Australia (Thompson 2008), and
water-ponding technologies are now being applied, for
example, to scalded rangelands in a number of African
and Middle Eastern countries, and in China and the
United States.
less expensive than dealing with major damage later
on. For example, treating an eroded slope with small
rills - that is, shallow channels (less than 0.3 m deep)
carrying runoff down slope after rainfall event - is far
easier and less costly than repairing deep, wide gullies
(Box 4.3 ).
Landscape-scale restoration success can be meas-
ured by general
indicators
, such as the aesthetics of
vegetation along a rehabilitated roadside, and by spe-
cifi c indicators, such as the absence of heavy metal
pollutants leaking from a reformed mine spoil. Whether
general or specifi c, we recommend using simple indica-
tors that serve as surrogates for diffi cult to measure
landscape processes. For example, directly measuring
the rate and amount of water running off a landscape
is technical and costly, but restorationists can quickly
estimate the amount of perennial vegetation cover
(Plate 4.1), which provides surface protection and
obstruction to fl ows of water and wind turbulences.
When ground cover is measured on a disturbed site
(Figure 4.6a) and compared to values from a reference
site (Figure 4.6b), this easily estimated cover value pro-
vides restorationists with a useful indicator of how well
a restored landscape is progressing over time towards
developing a cover that reduces the rate and amount
of runoff, hence improving the amount of water
retained and stored in the landscape.
Selecting which indicators to measure is diffi cult
given the large number of ecosystem indicators
described in scientifi c papers and topics (e.g. Costanza
et al
. 1992 ; Munoz - Erickson
et al
. 2007 ). Given that
our main interest in this chapter is on the functionality
of biophysical processes in landscapes, we list 25 indi-
cators assessed by the Landscape Function Analysis
monitoring procedure that can provide restorationists
with useful information about landscape processes
(Table 4.1). This list is based on our experiences with
restoration projects in a wide range of landscapes
around the globe (e.g. Tongway & Ludwig 1997, 2002,
2007). For convenience, we group these 25 indicators
into four groups: landscape organization, soil surface
condition, ephemeral drainage-line stability and vege-
tation structure. These four groups of
indicators
are
fully described in Tongway and Ludwig (2011, chs.
13-16). Landscape Function Analysis documents
explaining how to assess or score indicators are avail-
able as PDF fi les online at http://members.iinet.net.
au/∼lfa_procedures/, along with spreadsheets that are
