motivation of farmers to establish soil conservation measures on sloping land. This
field study reveals that information and training on soil-water interdependencies, as
well as the disclosure of important information among stakeholders, are
prerequisites for appropriate flood responses at the institutional and practical
level. Furthermore, decision-makers need to understand how local residents go
about developing their own causal explanations of flood events, rather than developing mitigation strategies based solely on expert findings and narrow hierarchical
structures and economic constraints (Schad et al. 2012). Although structural
measures, such as dams or overspills, are crucial in preventing floods and
diminishing their adverse impacts, they alone are not effective future flood mitigation strategies. Rather, structural measures should be carefully combined with nonstructural measures such as community based zoning in flood-prone areas and the
development of land use plans, those that build on both expert and local knowledge
(Schad et al. 2012).
3.4 The Impact of Reservoir Management on Nutrient
Redistribution to Irrigated Lowlands
4
Erosion and landslides on steep slopes are a common problem in intensively farmed
Southeast Asian mountainous headwater systems, and create tremendous sediment
fluxes. Globally, 197 Tg of particulate organic C and 30 Tg of particulate nitrogen
(N) is transported through rivers on a yearly basis, from which the Asian river
network contributes up to 50 % (Beusen et al. 2005). The effect of upland intensification on downstream areas is complex, due to: (1) matter reallocation as a result of
non-linear and scale-dependent biophysical processes. Flux estimations of sediment
associated nutrients have a high spatio-temporal variability at the catchment scale,
as they integrate various biochemical and biophysical processes (King and Harmel
2003; Gao 2008), (2) land use intensification and socio-economic policies, as well
as linear features (e.g., roads, footpaths and canals), stimulating erosion processes
and conveying sediments in tropical mountainous regions throughout Southeast
Asia (Ziegler et al. 2000, 2004), and (3) reservoirs and irrigation channels being
constructed throughout the area in order to support rice intensification during the
dry season. These anthropogenic changes alter the natural water regimes in mountainous areas significantly, and can be expected to contribute to the reallocation of
C and N, as they capture and transport the overland flow from intensified upland
areas. Reservoirs acting as a sediment trap are a known phenomenon, and after the
construction of reservoirs in Hoa Binh and Thac Ba in northern Vietnam, sediment
delivery to the Red River delta was found to decrease by between 56 % and 74 %. It
was also estimated that an additional 20 % decrease would occur if two more
reservoirs were to be constructed (Le et al. 2007). As a result, reservoir
4 Written by Petra Schmitter.
126
H.L. Fro ¨hlich et al.
field study reveals that information and training on soil-water interdependencies, as
well as the disclosure of important information among stakeholders, are
prerequisites for appropriate flood responses at the institutional and practical
level. Furthermore, decision-makers need to understand how local residents go
about developing their own causal explanations of flood events, rather than developing mitigation strategies based solely on expert findings and narrow hierarchical
structures and economic constraints (Schad et al. 2012). Although structural
measures, such as dams or overspills, are crucial in preventing floods and
diminishing their adverse impacts, they alone are not effective future flood mitigation strategies. Rather, structural measures should be carefully combined with nonstructural measures such as community based zoning in flood-prone areas and the
development of land use plans, those that build on both expert and local knowledge
(Schad et al. 2012).
3.4 The Impact of Reservoir Management on Nutrient
Redistribution to Irrigated Lowlands
4
Erosion and landslides on steep slopes are a common problem in intensively farmed
Southeast Asian mountainous headwater systems, and create tremendous sediment
fluxes. Globally, 197 Tg of particulate organic C and 30 Tg of particulate nitrogen
(N) is transported through rivers on a yearly basis, from which the Asian river
network contributes up to 50 % (Beusen et al. 2005). The effect of upland intensification on downstream areas is complex, due to: (1) matter reallocation as a result of
non-linear and scale-dependent biophysical processes. Flux estimations of sediment
associated nutrients have a high spatio-temporal variability at the catchment scale,
as they integrate various biochemical and biophysical processes (King and Harmel
2003; Gao 2008), (2) land use intensification and socio-economic policies, as well
as linear features (e.g., roads, footpaths and canals), stimulating erosion processes
and conveying sediments in tropical mountainous regions throughout Southeast
Asia (Ziegler et al. 2000, 2004), and (3) reservoirs and irrigation channels being
constructed throughout the area in order to support rice intensification during the
dry season. These anthropogenic changes alter the natural water regimes in mountainous areas significantly, and can be expected to contribute to the reallocation of
C and N, as they capture and transport the overland flow from intensified upland
areas. Reservoirs acting as a sediment trap are a known phenomenon, and after the
construction of reservoirs in Hoa Binh and Thac Ba in northern Vietnam, sediment
delivery to the Red River delta was found to decrease by between 56 % and 74 %. It
was also estimated that an additional 20 % decrease would occur if two more
reservoirs were to be constructed (Le et al. 2007). As a result, reservoir
4 Written by Petra Schmitter.
126
H.L. Fro ¨hlich et al.