Ecological Impacts of Dams on Vegetation Communities and Pattern Using GIS: A Case Study of Wadi Ma?awil Catchment

Dams are a human innovation to reduce flood hazards and to provide water for irrigation and domestic use. In Oman, dams also slow the water flowing through natural wadis, increasing infiltration into subsurface zones. At the same time, dams could ecologically disturb the habitat and the ecosystems downstream. This study is aimed at documenting the changes in the vegetation and soil properties in upstream and downstream areas of Ma?awil dam. This research will examine the potential impacts of the Ma?awil dam in reducing sedimentation transport downstream. Our hypothesis is that the dam will reduce the supply of sediments to downstream areas, and there will also be change in the habitat in upstream and downstream area. These reductions in sediment will have major impacts on wadi channel geomorphology, and in plant and animal habitat. Despite the fact that several dams have been constructed in Oman, no attempt has been made to investigate these dams? impact from an environmental point of view. The main objective of this study is to investigate habitat change or shift due to interference with the natural process of sedimentation transport. The study will provide a database for future reference in mapping habitat change within the study area and a framework for study of other dams in Oman.

Dams are a human innovation to reduce flood hazards and to provide water for irrigation and domestic use. In Oman, dams also slow the water flowing through natural wadis, increasing infiltration into subsurface zones. At the same time, dams could ecologically disturb the habitat and the ecosystems downstream. This study is aimed at documenting the changes in the vegetation and soil properties in upstream and downstream areas of Ma?awil dam. This research will examine the potential impacts of the Ma?awil dam in reducing sedimentation transport downstream. Our hypothesis is that the dam will reduce the supply of sediments to downstream areas, and there will also be change in the habitat in upstream and downstream area. These reductions in sediment will have major impacts on wadi channel geomorphology, and in plant and animal habitat. Despite the fact that several dams have been constructed in Oman, no attempt has been made to investigate these dams? impact from an environmental point of view. The main objective of this study is to investigate habitat change or shift due to interference with the natural process of sedimentation transport. The study will provide a database for future reference in mapping habitat change within the study area and a framework for study of other dams in Oman.

Dams are considered one of the most significant human interventions in the hydrological cycle (McCartney, 2009). Several studies have indicated that dams constitute obstacles for longitudinal exchange and flux of water, matter, and energy that result in ?discontinuities? in the water channel continuum along fluvial systems. This discontinuity creates a transformation or metamorphosis of channel morphology (Schumm, 1969; Ward and Stanford, 1995). Other studies reported changes in the ecology, biodiversity, types of plant species, growth, establishment and survival (Ellery et al., 1993; Auble et al., 1994; Qureshi et al., 2014; Nilsson and Berggren, 2000). It is worth noting that dryland fluvial processes are different than those of humid regions (Tooth, 2000). Semiarid fluvial systems are characterized by being very dynamic due to the episodic and torrential rains (Hooke, 2016). As a result, dryland rivers have extreme variability in flow and sediment transport (Bunn et al, 2006).Changes in the discharge and/or sediment load would disturb the existing quasi-equilibrium state and cause an adjustment of the channel form (Petts and Gurnell, 2005). Sediment transportation and re-distribution patterns play a major role in determining the geology, biology, and chemistry of the fluvial ecosystems. Chen et al (2008) and Forsberg et al (2017) attributed flourishing of vegetation to the nutrients supplied via sedimentation. Construction of six dams on the Amazon fluvial ecosystem substantially increased the biodiversity and productivity of the Amazon River system (Forsberg et al, 2017). Another example from arid southeastern Australia found that a constructed dam diverted water and had a negative influence on breeding in a colonial nesting species in the Macquarie Marshes (Kingsford and Johnson, 1998). A study carried out in the Hammami Plain in Iran indicated an undesirable impact of dams on the downstream ecology by causing deterioration in the plant and animal habitats (Ataei et al, 2017). Damming is very likely to reduce biodiversity and ecosystem service values of both aquatic and terrestrial ecosystems within the water catchment (Grumbine and Xu, 2011). Researchers have documented the lack of sediment supplies to downstream sources impacting the lowland floodplains and deltas, causing loss of residential areas and farmlands due to increased flooding and subsidence (Syvitski et al, 2009; Schmitt, Rubin and Kondolf, 2017). For example, a significant decrease in the shoreline of the Mekong Delta is caused by trapping of sediments by a dam constructed upstream (Li et al., 2017). Accumulation of sediments inside and in the vicinity of dams creates a condition called ??sediment-shadow?? in the downstream of the catchment area when sediment-starved flows commonly erode channel boundaries and create long-term channel instabilities and erosion (Asaeda et al., 2010; Wohl and Rathburn, 2003; Milliman and Farnsworth, 2013; Rajendran, 2015). Channel erosion changes and widening result in losses in riparian habitats and vegetation (Schmidt and Wilcock, 2008; Zimmerman et al, 2010; Dang, et al., 2014; Pal, 2017). In Oman, there are 114 dams that serve a variety of purposes including surface retention, recharge, and flood protection (MRMWR, 2010; Myanmar, 2012). Between 1985 -2011 Oman built 43 recharge dam including 21 recharge dams constructed to intercept ephemeral wadies flowing a cross the alluvial fans of Al-Batinah region (MRMWR, 2012; Abdalla and Al-Rawahi, 2013). Al- Khod recharge dam has the biggest storage capacity (11.55 million m3), followed by Wadi Al Ma?awil (10.00 million m3) (MRMWR, 2010). The estimated total amount of rain lost to the sea and desert, if not intercepted by dams, is about 120 million m3 per year (Abdel-Rahman and Abdel-Magid, 1993). Recharge dams in Oman intercept a sizable amount of runoff during rain events and have deprived the coastal plains of the silt and other fertile fine sediments carried by wadies down the valley (Al-Ismaily et al, 2013; Abdel-Rahman and Abdel-Magid, 1993; Abdalla, and Al-Rawahi, 2013). Depravation of silt to downstream areas could influence the establishment or the survival of the existing plant communities negatively. Recently, several studies have focused on the impact of recharge dams on the sedimentological patterns, hydropedological characteristics and geomorphological properties of top soil and the parent material below (Al-Ismaily et al., 2013ab; Al-Maktoumi, 2015; Rajendran, 2015; Al-Saqri 2016; Faber et al, 2016; ). Limited studies also covered the role of recharge dams in mitigating seawater intrusion (Abdalla and Al-Rawahi, 2013) and the microbiological aspects of dam reservoir soils (Victor, 2002; Al-Sadi, 2017). Dam construction played role in reducing the biodiversity and the value of ecosystem service for both aquatic and terrestrial ecosystems within the watersheds (Grumbine and Xu, 2011; Al-Robi et al, 2018). Dams also affect the shoreline vegetation and alter the plant communities around them (Qureshi et al., 2014). There have been no studies; however, that assesses the effect of dams on the growth of plant communities across the alluvial soils of the Al-Batinah region. In addition, with sediment transport disturbance and Sea Level Rise (SLR), the existing farmlands, built area and natural habitat in lowland areas is vulnerable and the sustainability of the downstream area is at risk. As sediments are trapped upstream, degradation of floodplain, coastal environments and a shift or disappearance in habitat pattern and changes in vegetation communities is taking place. Therefore, understanding of the natural functioning and variability of semiarid fluvial systems is important in terms of landscape dynamics and for management purposes. It?s very challenging to manage a dam in a way that provides minimal alteration to ecological health and ecosystem services. Hence, the aim of this study is to conduct a comprehensive investigation to establish baseline data on the effects of recharge dam construction and existence on the soil properties and vegetation structure and distribution of plant communities at the upstream and downstream areas of the dam. We plan to use the upstream and downstream areas of the Ma?awil dam located at Wadi Ma?awil watershed as our main focal study area.