Elsevier

Ecological Engineering

Volume 74, January 2015, Pages 458-462
Ecological Engineering

Short communication
Soil bioengineering application for flood hazard minimization in the foothills of Siwaliks, Nepal

https://doi.org/10.1016/j.ecoleng.2014.11.020Get rights and content

Highlights

  • Banks of an ephemeral stream were almost fully stabilized.

  • Ipomoea fistulosa plants were found very effective for the flood control mechanism.

  • Vegetation based solutions are found to be more effective than the mechanical methods of stream bank stabilization.

Abstract

This study focused on soil bioengineering for stream bank stabilization. Both vegetative check dams and wire net check dams along with vegetation were used during May–June 2009. After three growing seasons, the banks of the ephemeral stream were almost fully stabilized. The effects of river edge cuttings were highly reduced, and flow channels of the river were also narrowed. Vegetation based solutions are found to be more effective than the mechanical methods of stream bank stabilization. Vegetation application on flood-damaged bare ground was also found to be very successful. Furthermore, some plants species showed almost equal growth performances on both flood-affected and unaffected bare ground.

Introduction

Soil bioengineering techniques (SBT) have been carried out for centuries to control erosion problems on slopes and along riverbanks in different parts of the world (Schlueter, 1986, GEO, 2000, Fatahi et al., 2010, Bariteau et al., 2013). Sound engineering practices are employed in conjunction with integrated ecological principles, using living vegetation and other non living plant materials to stabilize slopes (hill-slopes, riverbanks, and lake/shorelines), to protect wildlife habitats, and to enhance the functioning of ecosystems (Gray and Sotir, 1996). In recent years, SBT have been extensively used because they are cost-effective, flexibile, and applicable in remote areas by using locally available materials, and because they require low-cost labor in comparison to more elaborate civil engineering works (Li and Eddleman, 2002, Wu and Feng, 2006, Li et al., 2006, Evette et al., 2009, Rey and Burylo, 2014).

Vegetation-based techniques have been applied either alone or in conjunction with small-scale civil engineering structures to reduce shallow-seated instability erosion on slopes and stream banks. Engineering functions and hydrological effects of vegetation are key factors to control soil erosion and to stabilize slopes (Dhital et al., 2013a). Vegetation efficiently mitigates erosion by active or passive protection (Rey et al., 2004). Active protection against erosive agents consists of rain drop interception (Woo et al., 1997), an increase in water infiltration in soil (Cerdà, 1998), and soil fixation by root systems (Gyssels and Poesen, 2003). Vegetation also has a passive action by trapping and retaining sediment inside the catchment due to its aerial parts (Abu-Zreig, 2001). Selection of plant species is very important due to potential weather scenarios in terms of its capacity of the root reinforcement and evapotranspiration (Normaniza et al., 2008, Stokes et al., 2010). However, species used for soil bioengineering should have pioneer plant character, and fast and simple propagation (Weigel et al., 1987). Furthermore, altitude range, local geology, light requirements, availability of plant species, and nutrients are other essential factors for the vegetation succession.

In river channels, vegetation reduces near-bed shear stress, and controls sediment erosion, transport and deposition processes by its resistance to flow and the capacity of roots to modify substrate cohesion (Brookes et al., 2000, Bennett et al., 2002, Corenblit et al., 2007). Stem density and diameter are key-parameters controlling bed load transport in open channels which may lead to significant sediment accretion in fluvial corridors during floods (Samani and Kouwen, 2002, Ishikawa et al., 2003). Furthermore, large structure of vegetation helps to reduce or minimize sediment supplied to the river by slumping and other types of mass failure (Williamson et al., 1996, Hubble et al., 2010). However, large woody debris sometimes may cause flooding during the time of high intensity of rainfall.

SBT have been widely used in Nepal to deal with erosion problems on slopes, especially for treatment of shallow-seated landslides associated with high way construction (Clark and Howell, 1992, Lawrance, 1994, Howell, 1999, Florineth et al., 2002, Sharma, 2004, Lammeranner et al., 2005, Devkota et al., 2006, Ojha and Shrestha, 2007, Mathema and Joshi, 2010). However, the majority of published literature is based on practical experience and not on scientific research that uses data about initial soil conditions and modes of failure. Compared to observations from the application of SBT to landslide treatment, very few soil bioengineering works have been done on stream bank protection, which requires the combined efforts of the local community, private consultants and the Nepal government. Furthermore, no scientific reports of SBT for flood hazard minimization in Nepal exist to this date. Bank cutting, farmland inundation, and extensive erosion of agricultural land are common problems during every annual monsoon in the Siwaliks and Terai regions of Nepal. In this context, an experiment was conducted with two objectives (1) understanding how to stabilize the banks of an ephemeral river and (2) minimizing the impacts of flooding on flood-damaged bare grounds in the foothills of the Siwaliks.

Section snippets

Study area

The study site lies in Hariwan Village Development Committee – 1 at the edge of ephemeral stream (Bilandhi Khahare River) in the lower watershed of Bagmati River Basin, Nepal, 36 km from District Headquarters, Sarlahi (Fig. 1). The surrounding region is called the foothills of the Siwalik, a region known as the most unstable and natural hazard prone area in Nepal because of its weak geological formation. Debris flows and landslides in the upper part and flooding in the lower of this region

Materials and methods

A small catchment area (48 ha) with severe flood damages was selected for the experimental study with the cooperation of District Soil Conservation Office, Sarlahi, Nepal. A monitoring committee at the local level with the collaboration of local government bodies was formed in June 2009. A social vulnerability flood hazard map was prepared to identify unstable sections of both river banks and nearby flood-affected bare grounds. Initially, the monitoring committee managed a controlled cattle

Results and discussion

After three growing seasons, it was found that the banks of the ephemeral stream were almost fully stabilized and most parts of the bare ground were covered with more shrubs and grasses than had been planted. Vegetative check dams were very effective in controlling soil erosion and as a flood control mechanism, with I. fistulosa stem cuttings continuously extending on both sides of the check dams (Fig. 2). The effects of edge cuttings were highly reduced, and flow channels of the river were

Conclusions and recommendations

SBT such as live vegetative check dams appear to be one of the best solutions for flood hazard minimization in the foothills of Siwaliks, Nepal. I. fistulosa plants are very effective as a flood control mechanism when combined with vegetative check dams. Bamboo combinations for check dam construction and planting of bamboo behind check dam are both very useful for stream bank stabilization. Furthermore, vegetation-based solutions are also very cost effective compared to mechanical methods for

Acknowledgements

This work was partially supported by the National Basic Research Program of China (Grant No. 2012CB955403), National Natural Science Foundation of China (Grant No. 41171031), and Hundred Talents Program of the Chinese Academy of Sciences. We would like to thank District Soil Conservation Office and local community of Hariwan Village Development Committee-1, Sarlahi, Nepal for their valuable information and involvement during the field work. We also acknowledge Prof. N. LeRoy Poff for his

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