Gully plug (Jordan)

Gully plugs aim at rehabilitating active gullies in dryland watersheds, which are prone to erosion through concentrated surface runoff. Multiple gullies plugged in succession dissipate runoff energy, foster local water retention and infiltration, encourage sedimentation, assist in the stabilization of gully bed and side banks, and stimulate revegetation of flow paths; the channel measures must be combined with proper SLM in the catchments upstream.

Characteristics: Multiple gully plugs positioned sequentially within a gully system interrupt concentrated surface runoff and reduce its erosive power. The plugs are each made of multiple cobbles/stones mostly ranging between 10 and 30 cm diameter and constructed to ensure a stable structure. The plugs started at the head of the gully (upstream) and ranges from 1.5 - 3.7 m in width with an average of 2.5 m. For heavily eroded and very unstable sections, gabions can be used also. The structures are around 1.0 to 1.5-m high, anchored into the sidewalls, and around 0.20 to 0.35 m deep into the gully bed, built up to around 1/3 to max. 1/2 of the gully depth - ensuring the concentrated flow stays within the channel and does not overflow the side banks. The top of the plug is U-shaped, with the sides built higher than the centre. Upslope, the plugs are packed with soil to trap sediments (stopping it flowing through the structure), and downslope the plugs have an apron to dissipate the energy of overflowing water, into a micro stilling basin. The downslope side of the gully plug is sloped rather than vertical. The large stones add roughness to the slope, creating a rough spillway that dissipates erosive energy. In the direction of gully flow, several gully plugs are placed such that the upper gully apron is set at approximately the height of the following downstream gully crest.

Environment: The technology is used in a watershed close to Al Majeddyeh village, located in the Middle Badia zone, approximately 30 km south-east of Amman. The climate is arid and warm (Palmer, 2013). The average annual rainfall is around 130 mm. The natural environment is labelled as steppe, “BSh” in the köppen classification. The human environment is characterized by agropastoralists. They are semi-nomadic and live in villages around the watershed, for example, Al Majeddyeh village.

Purpose: The measure interrupts the concentrated flow, reduces velocity, and dissipates energy. Multiple structures along the gully decrease the erosive power of runoff, retaining a fraction of the runoff, inducing sedimentation (upstream of the plug), thus protecting the gully bed from further deep-scouring, and strengthening the gully side banks, especially when this is linked with re-vegetation. Over time, the establishing vegetation (roots and surface cover) stabilizes the soil and protects it from concentrated flow erosion. To be effective, gully plug emplacement requires SLM in upland areas. These measures then jointly mitigate peak runoff generation and accordingly reduce downstream flooding.

Major activities: Upland SLM is essential. In the specific watershed rehabilitation context, upland SLM was achieved through micro water harvesting and re-vegetation through native shrubs (the “VALLERANI” method). Gully morphology assessment is required for gully plug design, and positioning and earthwork excavation is necessary for foundation preparation in the gully bed and wall anchors. Proper layering of various size stones and shaping of gully plugs is necessary as is the addition of a packed soil pack upstream of the stone structure, to semi-seal the surface and to pond water. Then gully walls are revegetated through native seedlings: these benefit from the water ponding upstream prior to sedimentation upstream of the gully and enhanced soil water storage in the sediments once the gully is filled.

Benefits: Stops ongoing land degradation and gully deepening, and achieves a certain degree of rehabilitation; retains a fraction of runoff water and sediments in the watershed – water mainly infiltrates and provides moisture to the gully vegetation; gully vegetation serves various purposes including livestock fodder, reduction of flow velocities in the gully, and retention of further sediment.

Land user's opinion: Land users benefit from the vegetation (e.g. fruit trees can potentially be out-planted), as well as ponded water for livestock; however, the technology is labor-intensive, and therefore costly, and landowners (at the local target site) require incentives to carry out the work.

Location: Amman governorate/Al Jizza/Al Majeddyeh village, Jordan

No. of Technology sites analysed: single site

Spread of the Technology: applied at specific points/ concentrated on a small area

In a permanently protected area?: Nee

Date of implementation: 2017

• through land users' innovation
• as part of a traditional system (> 50 years)
• during experiments/ research
• through projects/ external interventions