Assessing erosion processes associated with ...

An ASABE Meeting Presentation DOI: 10.13031/aim.20162461210. Paper Number: 16-2461210

Assessing erosion processes associated with establishment of coal seam gas pipeline infrastructure in Queensland, Australia Cameron A. Vacher1, Diogenes L. Antille1,*, Neil I. Huth2, Steven R. Raine3 1

University of Southern Queensland, National Centre for Engineering in Agriculture, Toowoomba, QLD, Australia, 2CSIRO, Toowoomba, QLD, Australia, 3University of Southern Queensland, Institute for Agriculture and the Environment, Toowoomba, QLD, Australia. *Corresponding author, E: [email protected], Ph: +61-7-46312948.

Written for presentation at the 2016 ASABE Annual International Meeting Sponsored by ASABE Orlando, Florida July 17-20, 2016 Abstract. In Queensland, Australia, the largest known, proven, onshore reserves of coal seam gas (CSG) are found in the Surat and Bowen Basins, which occupy an area of approximately 300,000 km2. This area includes both grazing and highlyproductive cropping lands. Establishment of CSG-related infrastructure such as pipelines and associated right of way to transport gas and water from extraction points through to processing and export facilities is one of the major types of land disturbance observed in this region. Pipeline right of way areas include trench lines as well as the adjoining traffic zones required for trench line construction, pipe installation and access to sites. The primary forms of disturbance within the right of way areas include: (1) Soil compaction and changes in hydraulic properties, (2) Changes in soil chemistry such as carbon and nutrients, and exposure of potentially reactive or poorer quality subsoil (e.g., saline, sodic or acidic subsoil), (3) Changes in texture due to risk of soil blending and layer inversion, and (4) Changes in topography and natural drainage lines due to soil leveling, topsoil stripping and stockpiling, subsidence, and establishment of surface erosion control infrastructure. These disturbances contribute to poor vegetation establishment, tunnel and surface erosion, further influenced by lack of surface cover, with continuing decline in soil productivity and functions, and increased risk of sediment and nutrient discharge to watercourses. Impacts of soil compaction, surface cover, soil physico-chemical properties, and changing hydrology were measured to parametrize the Water Erosion Prediction Program (WEPP) and SIBERIA landform evolution models. Both models provided a reasonably good indication of the sensitivity of soil and field conditions to potential degradation processes caused by CSG pipeline right of way installations. The landform modeling also provided an indication that within the assessed field layout and soil type, the industry practice of installing a mound to account for settlement or subsidence of soil in the trench does not generate greater erosion rates than undisturbed field areas, whilst unmanaged settlement or subsidence has the potential to generate significantly higher erosion, and therefore greater potential for gully development. Results derived from this work will inform industry guidelines for improved management of the soil resource for joint CSG-agricultural lands.

Keywords. Environmental footprint, Erosion processes modeling, Hydrologic processes, Sediment transport. The authors are solely responsible for the content of this meeting presentation. The presentation does not necessarily reflect the official position of the American Society of Agricultural and Biological Engineers (ASABE), and its printing and distribution does not constitute an endorsement of views which may be expressed. Meeting presentations are not subject to the formal peer review process by ASABE editorial committees; therefore, they are not to be presented as refereed publications. Citation: Vacher, C. A., Antille, D. L., Huth, N. I., Raine, S. R. (2016). Assessing erosion processes associated with establishment of coal seam gas pipeline infrastructure in Queensland, Australia. ASABE Paper No.: 16-2461210. St. Joseph, Mich.: ASABE. DOI: 10.13031/aim.20162461210. For information about securing permission to reprint or reproduce a meeting presentation, please contact ASABE at [email protected] or 269-932-7004 (2950 Niles Road, St. Joseph, MI 49085-9659 USA).

Introduction Soil security, food supply and energy supplies are critical pressing issues facing the world today. In Eastern Australia (Queensland and New South Wales), concerns have been raised over continuous expansion of coal seam gas (CSG) activities, which could impact on long-term agricultural productivity and environmental sustainability through threats to surface and groundwater resources, loss of agricultural land to infrastructure developments, and adverse effects on soil resources (Owens, 2012; Swayne, 2012). The existing policy for protecting Queensland’s strategic cropping land (SCL) states that development on such lands that temporarily diminishes its productivity will, at the end of the development, restore the land to strategic cropping land condition (DERM, 2010). A balanced co-existence of mining and agriculture is suggested as possible, but requires careful management (Huth et al., 2014). Evidence pertaining to overseas experience has noted that well pad development is a far lesser landscape disruption than the extensive network of associated pipelines from gas development (Drohan and Brittingham, 2012). Current measurements from Queensland CSG areas indicates a similar situation with the spectrum of impacts occurring on the soil resource due to pipeline installation, including textural, structural and chemical degradation, resulting in areas of highly impacted surface and subsurface hydrology, and increased erosion potential (Antille et al., 2014; Vacher et al., 2014). The long-term impacts of these degradation processes include reduced vegetation establishment and crop productivity, and increased potential for sediment delivery to waterways. The application of rehabilitation practices to restore the quality of strategic cropping land are typically conducted shortly after installation, but are limited for correcting elements of soil structural changes and modified hydrologic processes due to short-term rehabilitation requirements. The objectives of the work reported in this paper were to parametrize the Water Erosion Prediction Program (WEPP) and SIBERIA landform evolution models (Willgoose et al, 1989; Ascough II et al., 1997; Hancock, 2004; Hancock and Willgoose, 2004) to: (1) Assess the sensitivity of soil and field conditions to potential degradation processes caused by CSG pipeline right of way installations, and (2) Determine whether industry practice of installing a mound to account for subsidence of soil in the trench generated greater erosion rates than undisturbed field areas. Regional Description The majority of current and planned future developments in the CSG industry in Eastern Australia are concentrated within the Surat and Bowen Basins, Queensland (GISERA, www.gisera.org.au). The Surat Basin occupies approximately 300,000 km2 of central southern Queensland and central northern New South Wales. The Bowen Basin covers an area of approximately 60,000 km2 of central Queensland (Geoscience Australia, 2008). The Surat Basin is currently undergoing extensive CSG development with little mining present, while the Bowen Basin has historically had extensive coal mining with the majority of CSG in the planning stage (DNRM, 2014). Agricultural productivity within this area is linked to both soil type and water supply (rainfall and irrigation). Rainfall for the area (Figure 1) is summer dominant (≈70% of total rainfall occurs between October and March), with approximately 650 mm of average annual rainfall. The main soil types within the study area are Vertosols, commonly referred to as Black, Grey or Brown Earths, respectively (MacKenzie, 2004). These soils are characterized by relatively high clay contents (>35%) with shrink-swell properties, which cause deep and wide cracking on drying (Dinka et al., 2013). In Australia, Vertosols have a high value for agricultural productivity due to relatively high water holding capacity and potential nutrient store. Vertosols are prominent in the Surat Basin region impacted by CSG operations (Isbell, 2002). Erosion risk is generally low due to low natural gradients and high potential for grass cover establishment. However, Vertosols can be exposed to erosion and runoff if disturbed (e.g., compaction, tillage), and under low surface cover (Freebairn et al., 1996; Melland et al., 2016).

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Monthly rainfall (mm) (Miles, Queensland)

100 80 60 40 20 0 Jan

Feb Mar Apr May Jun

Jul

Aug Sep Oct Nov Dec

Figure 1. Long-term average monthly rainfall (1885-2016) recorded for the town of Miles, Queensland (Source: Bureau of Meteorology, Australian Government, http://www.bom.gov.au/).

Coal Seam Gas Impacts The most common range of direct soil impacts caused right of way operations can be broadly defined under the following: (1) Soil surface disturbance, (2) Soil compaction, and (3) Soil blending and layer inversion (Vacher et al., 2014. A typical pipeline installation right of way is presented in Figure 2.

Figure 2. Indicative right of way layout for pipeline installation (Source: APIA, http://www.apga.org.au/); trench line disturbance (red), traffic compaction zone (blue), and topsoil spreading (grey).

The range of impacts indicated above results in changes in soil physical, chemical and biological characteristics (Haigh and Sansom, 1999; Loch, 2000; De la Vega et al., 2004; Spoor, 2006; Alaoui et al., 2011; Batey, 2015). Although industry and pipeline manufacturing guidelines exist on best practice for effective pipeline installation, soil management, and re-compaction during backfilling Australian Pipeline Industry Association (APIA) code of practice (APIA, 2013), there are common cases of pipeline subsidence, surface and tunnel erosion occurring across the Surat and Bowen Basin (Figure 3). The depression zone caused by subsidence or tunnel erosion increases the potential for additional runoff volumes through interruption of the natural flow of surface water from upslope catchment areas. As a result, significant volumes to the concentrated flow can be added, which increases the erosion potential relative to the upslope catchment area (Olson and Doherty, 2012).


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Figure 3. Coal seam gas right of way on a Vertosol used for arable cropping showing ponding, subsidence, and changes to overland flow paths, respectively (Source: The Authors).

In addition to subsidence and tunnel erosion on trench lines contributing to increased potential for erosion at the field- and catchment-scales, impacts from soil surface disturbance (e.g., compaction and soil mixing or layer inversion) on right of ways can further exacerbate such erosion processes. Based on a previous study by Vacher et al. (2014), these impacts are: 

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Surface disturbance: removal of vegetative cover, which can result in loss of soil flora and soil organic matter cycling, and has direct impact on soil surface resistance to erosion processes (raindrop impact and runoff) (Ghadiri and Payne, 1986; Franti et al., 1999). Soil compaction: structural degradation resulting from loads applied to soil. This process reduces soil porosity and pores connectivity, and consequently water infiltration, holding capacity, and exchange of gases between the soil and the atmosphere (Rashid et al., 2015). Increased compaction also decreases vegetation cover, which leads to increased runoff (Loch, 2000; Bahir et al., 2015) and flow concentration resulting in higher erosion rates for adjoining areas, and Soil blending and layer inversion: occurs when soil layers are not properly segregated during excavation, stockpile or re-spreading. Detrimental impacts are greatest in situations where the subsoil exhibit undesirable physico-chemical properties (e.g., saline, sodic, or acidic, and with low aggregate stability). Such properties are common in Sodosols, Chromosols, and some Vertosols present in Queensland’s gas fields. A potential result for Sodosols in particular, and Vertosols with sodic subsoil, is placement of sodium-rich subsoil towards the surface that is prone to dispersion, surface crusting, and erosion (Vacher et al., 2004; Hardie et al., 2007).

Sudy Area This study is being undertaken near the towns of Miles and Chinchilla (Queensland), where CSG operations resulted in construction of collection and distribution pipelines on Vertosols soils. The study area is cropped on a biannual or annual basis, depending on rainfall patterns. Multiple pipeline installation is undertaken (gas and water pipes, respectively) with no significant installations in the previous 5 years. Right of ways often exhibit limited vegetation cover, as shown earlier in Figure 3. Subsidence and changes to natural surface flows were visible on right of ways of the study area (Figure 4), with depressions typically in the rage of 100-200 mm. Due to the deep profile of Vertosols, soil inversion or blending can be difficult to determine, however, increased compaction (by ≈15-20%) was observed below the topsoil (depth range: 100-300 mm). Aerial imagery with elevation data provides an indication of surface flow patterns of the paddock, including potential surface concentration along the right of ways of the area. General gradient in the study area are low (≤1%), and typical of Grey Vertosols in southern Queensland.


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Figure 4. An image showing surface water flow patterns within a gas field and along a coal seam gas right of way; impacted area is indicated in rectangle (Source: Huth et al., 2015).

Erosion Modeling The Water Erosion Prediction Program (WEPP version 2012.8) (Flanagan and Livingston, 1995; Flanagan et al., 2007) was used to simulate a range of slope conditions for a Grey Vertosol. Hillslopes were modeled to assess the sensitivity to slope and soil characteristics, as well as to generate parameters for the SIBERIA landform evolution model (Willgoose et al, 1989). The SIBERIA model was used to assess the sensitivity of soil erosion processes in relation to catchment and flow path characteristics. Sensitivity modeling was conducted with bare soil parameters (0% crop canopy and residue cover) to remove the uncertainty of crop success and also simulate a worst case scenario for the landforms. Further research is being conducted to simulate the sensitivity of the landforms with crop and management practices on the undisturbed field and right of way zones. WEPP Erosion Modeling Runoff and erosion simulations of a range of slope conditions were conducted using the WEPP model. The erosion component of the program uses a steady-state sediment continuity equation as the basis for erosion computations, as follows:   

Soil detachment in interrill areas is calculated as a function of the effective rainfall intensity and runoff rate, and If the flow hydraulic shear stress is greater than the soils critical shear, rill erosion will be predicted, which includes limitations in relation to flow sediment transport, When sediment load is greater than the capacity of the flow to transport it, deposition in rills will be predicted. Soil detachment rates incorporate elements of soil management including ground cover, canopy cover, and buried residue.

Either a single event rainfall hydrograph (time vs. cumulative rainfall) or long-term climate file data with daily event data can be modeled. For long-term climate data simulations, each daily time step predicts runoff and soil loss, which is most sensitive to: rainfall depth (mm), rainfall duration (h), peak rainfall intensity (mm h-1, measured as a ratio of event average intensity), and time to peak rainfall intensity (Nearing et al., 1990; Flanagan and Nearing, 1995). The primary WEPP soil characteristics assessed for the Grey Vertosol of the study area are:    

Interrill erodibility, Ki =3.85×10-6 kg s m-4, Rill erodibility, Kr =6.91×10-3 s m-1, Critical shear, Ʈc =3.50 N m-2, and Effective hydraulic conductivity, He =2.94 mm h-1.


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Similar value parameters were used by Reichert and Norton (2013) for Grey Vertosols. The above parameters are indicative of soil with limited erosion resistance under bare soil conditions. The primary parameter that can be changed to increase or decrease erosion stability is the soils effective hydraulic conductivity (infiltration rate) through amendments or vegetation to improve infiltration rates or disturbance (e.g., level of compaction) or contamination (e.g., increased sodicity). WEPP modeling was conducted on range of effective hydraulic conductivity values for a Grey Vertosol on a 1000-m long slope at 1.0% gradient (Figure 5, and Table 1). Results indicate relatively low levels of soil loss for the He of 3 (close to assessed soils data) and 5 mm h-1, with peak rates below 15 t ha-1 y-1 at the end of the slope (average sediment loss