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A Novel Methodology For Analysis Of Iwrm Achievements In Stormwater Quality Improvement

Congress: 2015
Author(s): Deonie Allen (Edinburgh, UK), Scott Arthur, Heather Haynes, Jen Morse, Alan Yeakley, Jenny Mant
Heriot-Watt University1, Portland State University2, River Restoration Centre3

Keyword(s): Sub-theme 8: Revisiting water paradigms,
AbstractAbstract

Integrated water resource management focuses on a key aim: the sustainable development and management of water as a resource. Sustainable urban drainage systems (SuDS) are one of the methods of achieving integrated water resource management (IWRM). SuDS form part of the blue-green stormwater management measures designed to achieve the multiple benefits (rounded sustainability) of stormwater management. This paper presents the catchment analysis method successfully used to assess sustainable stormwater management, and the key findings from IWRM implementation within these areas.

Introduction

Portland City, within the state of Oregon, USA, is considered to be one of the foremost 'green-blue' cities of the developed world due to its widespread adoption of integrated stormwater management systems. Within the 52 square mile Johnson Creek catchment, both urbanised and agricultural land has been retrofitted or newly designed specific to mitigating the volume and quality of runoff via wet (blue) or ephemeral (green) assets, such as green streets, setback outfalls and river restoration and remaindering. A setback stormwater outfall provides a short stretch of, often steep, vegetated overland flow path or informal naturalised channel prior to discharge entering the receiving waterway. Similar to a vegetated filter strip or swale, setbacks rely on natural surface and vegetation to decrease the velocity and detain pollutants in stormwater runoff, but generally receive a very low level of management or maintenance.

Green streets are the placement of biofiltration systems within road networks and parking areas to collect and treat road runoff. This source-based stormwater management is also widely complemented by extensive river restoration work (e.g. wooded corridors, floodplain restoration, river re-meandering, provision of back waters and shading) along the banks and floodplain of Johnson Creek and some of its tributaries. Within this study, restoration is defined as river bank and floodplain activities that have been planned and implemented by the local authorities (Johnson Creek Watershed and the Portland Bureau of Environmental Services). Given that this integrated blue-green system has been actively evolving for over 10 years, Johnson Creek provides an ideal locale to measure and review the effectiveness of these stormwater management assets at various stages of maturity.

Effective analysis of blue-green measures to achieve IWRM is a difficult task. Comprehensive analysis requires consideration of multiple catchments with similar anthropogenic influences, physical characteristics and a range of blue-green infrastructure. To achieve this analysis, a novel methodology has been devised and employed across the Johnson Creek watershed.

Methodology

During a 1 month period, 182 samples were collected from the outfalls of 54 catchments feeding urban stormwater runoff to the receiving waterway, Johnson Creek. A snap shot approach was taken to allow direct comparison of all sample water quality analyte concentrations. Samples from sediment deposits within the outlets and along the creek were collected and tested for a range of known urban pollutants (heavy metals).

The method to deconstruct the beneficial and detrimental effects of IWRM measures on the catchment (Johnson Creek watershed) focused on using geographic information system and stormwater outlet stormwater quality characteristic. A layered and sub-catchment approach was taken. The layered approach (Figure 1) defined the stormwater flow path was defined through overland and piped stormwater network. Each catchment was then defined relative to the flow path, from upper, mid and lower contributing catchment areas to a specific stormwater outfall to Johnson Creek. Land use was considered in impervious area and green space defined according to the location on this flow path, and weighted accordingly to illustrate the urban sub-areas contribution to the overall pollutant level of the catchment.

Figure 1: layered method of catchment description, prior to sub-catchment definition

Catchment specific water quality management measures were considered relative to the overall catchment and location within the flow path network. Implementation of bioretention systems within the road network or parks, setback of outfalls and the restoration of watercourse banks and re-meandering are the three blue-green elements implemented within the Johnson Creek watershed. The extensive range of catchments considered created a novel dataset of comparable managed and unmanaged catchments with a range of IWRM levels.

Results and discussion

The catchment description and deconstruction methodology discussed in this abstract presents a novel and effective IWRM analysis method. In the full paper the way in which a contributing catchment is described will be shown to be highly important. It will be concluded that catchment land use geographic description is complex rather than lumped, and requires multi-level definition if effective stormwater quality analysis is to be supported.

There are both active and passive blue-green measures that provide water quality benefits as part of IWRM. Active measures such as bioretention systems, created or retrofitted into the active urban development area, are effective but can also be complemented or alternated with less urban development intrusive methods such as setbacks. The results of this watershed water quality IWRM analysis will demonstrate and qualify the beneficial influence of catchments with bioretention systems and setbacks respectively.

Using this snap shot, detailed contributing catchment analysis method to assess IWRM achievements in water quality will be shown to be highly effective. It provides a watercourse level visualisation of urban pollutant and blue-green infrastructure impact and illustrates blue-green beneficial influence at a catchment level.

2011 IWRA - International Water Resources Association office@iwra.org - http://www.iwra.org - Admin