D.D. Hornby

Maintaining existing zoning systems using automated zone design techniques: methods for creating the 2011 Census output geographies for England and Wales

Automated zone-design methods are increasingly being used to create zoning systems for a range of purposes, such as the release of census statistics or the investigation of neighbourhood effects on health. Inevitably, the characteristics originally underpinning the design of a zoning system (eg, population size or homogeneity of the built environment) change through time. Rather than designing a completely new system every time substantive change occurs, or retaining an existing system which will become increasingly unfit for purpose, an alternative is to modify the existing system such that zones which still meet the design criteria are retained, but those which are no longer fit for purpose are split or merged. This paper defines the first generic methodology for the automated maintenance of existing zoning systems. Using bespoke, publicly available, software (AZTool), the methodology is employed to modify the 2001 Census output geographies within six local authority districts in England and Wales in order to make them suitable for the release of contemporary population-related data. Automated maintenance of an existing system is found to be a more iterative and constrained problem than designing a completely new system; design constraints frequently have to be relaxed and manual intervention is occasionally required. Nonetheless, existing zone-design techniques can be successfully adapted and implemented to automatically maintain an existing system. The findings of this paper are of direct relevance both to the Office for National Statistics in their design of the 2011 Census output geographies for England and Wales and to any other countries or organisations seeking to maintain an existing zoning system.

Understanding the controls on deposited fine sediment in the streams of agricultural catchments.

Excessive sediment pressure on aquatic habitats is of global concern. A unique dataset, comprising instantaneous measurements of deposited fine sediment in 230 agricultural streams across England and Wales, was analysed in relation to 20 potential explanatory catchment and channel variables. The most effective explanatory variable for the amount of deposited sediment was found to be stream power, calculated for bankfull flow and used to index the capacity of the stream to transport sediment. Both stream power and velocity category were highly significant (p ≪ 0.001), explaining some 57% variation in total fine sediment mass. Modelled sediment pressure, predominantly from agriculture, was marginally significant (p<0.05) and explained a further 1% variation. The relationship was slightly stronger for erosional zones, providing 62% explanation overall. In the case of the deposited surface drape, stream power was again found to be the most effective explanatory variable (p<0.001) but velocity category, baseflow index and modelled sediment pressure were all significant (p<0.01); each provided an additional 2% explanation to an overall 50%. It is suggested that, in general, the study sites were transport-limited and the majority of stream beds were saturated by fine sediment. For sites below saturation, the upper envelope of measured fine sediment mass increased with modelled sediment pressure. The practical implications of these findings are that (i) targets for fine sediment loads need to take into account the ability of streams to transport/retain fine sediment, and (ii) where agricultural mitigation measures are implemented to reduce delivery of sediment, river management to mobilise/remove fines may also be needed in order to effect an improvement in ecological status in cases where streams are already saturated with fines and unlikely to self-cleanse.

The Development of a GIS-Based Inventory of Standing Waters in Great Britain together with a Risk-Based Prioritisation Protocol

An inventory of standing waters (freshwater lakes and lochs) wasderived from Ordnance Survey digital map data at a scale of 1:50 000 and represents the most comprehensive survey of its kind for Great Britain. The inventory includes 43 738 water bodies in England, Scotland, Wales and the Isle of Man and contains basic physical data such as location, surface area, perimeter and altitude. Catchment areas were computed for water bodies with a surface area larger than 1 ha from a digital terrain model (DTM) using customised routines in a geographical information system (GIS). The resulting polygons were then used to derive catchment-related information from a variety of national datasets including population density, livestock density, land cover, solid and drift geology, meteorological data, freshwater sensitivity status, acid deposition and conservation status. Using data derived from the inventory a risk-based prioritisation protocol was developed to identify standing waters at risk of harm from acidification and eutrophication. This information is required by the Environment Agency, Scottish Environmental Protection Agency and the U.K. statutory conservation bodies to co-ordinate actions and monitor change under international, European and national legislation.

Is shrimp farming a successful adaptation to salinity intrusion? A geospatial associative analysis of poverty in the populous Ganges–Brahmaputra–Meghna Delta of Bangladesh

The Ganges–Brahmaputra–Meghna delta of Bangladesh is one of the most populous deltas in the world, supporting as many as 140 million people. The delta is threatened by diverse environmental stressors including salinity intrusion, with adverse consequences for livelihood and health. Shrimp farming is recognised as one of the few economic adaptations to the impacts of the rapidly salinizing delta. Although salinity intrusion and shrimp farming are geographically co-located in the delta, there has been no systematic study to examine their geospatial associations with poverty. In this study, we use multiple data sources including Census, Landsat Satellite Imagery and soil salinity survey data to examine the extent of geospatial clustering of poverty within the delta and their associative relationships with salinity intensity and shrimp farming. The analysis was conducted at the union level, which is the lowest local government administrative unit in Bangladesh. The findings show a strong clustering of poverty in the delta, and whilst different intensities of salinization are significantly associated with increasing poverty, neither saline nor freshwater shrimp farming has a significant association with poverty. These findings suggest that whilst shrimp farming may produce economic growth, in its present form it has not been an effective adaptation for the poor and marginalised areas of the delta. The study demonstrates that there are a series of drivers of poverty in the delta, including salinization, water logging, wetland/mudflats, employment, education and access to roads, amongst others that are discernible spatially, indicating that poverty alleviation programmes in the delta require strengthening with area-specific targeted interventions.

Getting the foundations right: spatial building blocks for official population statistics

When publishing official population statistics, many national statistical organisations define small areas termed ‘building blocks’ which are then aggregated into larger ‘output zones’ for data release. While output zones are known to have enormous influence on spatial analysis, there has not been any systematic analysis of the effect of building blocks on characteristics of output zones. This paper evaluates current international practice in building block design, identifying key conceptual and practical issues. Using the example of six local authorities in England and Wales, it employs automated zone design to evaluate the influence of two sets of building blocks (street blocks and postcodes) on output zone characteristics. Household-level census data, accessed under secure conditions, are used to evaluate the impact on both newly designed and maintained output zones. Postcodes are shown to be more effective building blocks than street blocks, providing more uniform population and household sizes, greater precision for matching postcoded data to census data, and enabling more zones to be maintained. However, street blocks deliver more compact output zones and greater internal homogeneity of tenure and accommodation type. The scale effect of the modifiable areal unit problem and the specific geographical patterning of variables are both shown to be important factors when designing building blocks. These findings have directly informed policies and processes for the 2011 Census in England and Wales and provide useful conceptual and practical guidance for any national statistical organisation or analyst designing their own building blocks. The paper concludes that some aspects of international building block design practice could be more effectively harmonised but that such design should always be nationally specific to incorporate locally varying conceptual and practical issues. Further research should extend this analysis to other building block types, notably grid squares.

Small Water Bodies in Great Britain and Ireland: Ecosystem function, human-generated degradation, and options for restorative action

Small, 1st and 2nd-order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream reaches, lakes and estuaries. However, the large geographic extent and high connectivity of these small water bodies with the surrounding terrestrial ecosystem makes them particularly vulnerable to growing land-use pressures and environmental change. The greatest pressure on the physical processes in these waters has been their extension and modification for agricultural and forestry drainage, resulting in highly modified discharge and temperature regimes that have implications for flood and drought control further downstream. The extensive length of the small stream network exposes rivers to a wide range of inputs, including nutrients, pesticides, heavy metals, sediment and emerging contaminants. Small water bodies have also been affected by invasions of non-native species, which along with the physical and chemical pressures, have affected most groups of organisms with consequent implications for the wider biodiversity within the catchment. Reducing the impacts and restoring the natural ecosystem function of these water bodies requires a three-tiered approach based on: restoration of channel hydromorphological dynamics; restoration and management of the riparian zone; and management of activities in the wider catchment that have both point-source and diffuse impacts. Such activities are expensive and so emphasis must be placed on integrated programmes that provide multiple benefits. Practical options need to be promoted through legislative regulation, financial incentives, markets for resource services and voluntary codes and actions.

Land Cover and Land Use Analysis in Coastal Bangladesh

Land cover and land use (LCLU) analysis is a central determinant of the current and future relationship between people and local ecosystem services. It provides the spatial basis for the integrated analysis of the study area. Historical change (1989–2010) is identified using classification techniques based on available satellite imagery supported by other data. Nine categories of LULC are identified; water, Bagda (brackish shrimp farming), Galda (freshwater prawn farming), agriculture (non-waterlogged), agriculture (waterlogged), wetlands and mudflats, mangrove, rural settlements and major urban areas. The analysis shows an increase in aquaculture (mainly replacing rice fields), with agriculture becoming more intermixed with settlements. Future LULC scenarios are determined based on stakeholder narratives.

Flow structure in large bedrock-channels: the example of macroturbulent rapids, lower Mekong River, South-east Asia: Flow structure in river rapids

The rate of bedrock channel incision is key to the understanding of landscape evolution. Theoretical models relate channel incision to sediment transport; the latter conditioned by the bed shear stress. However, theory is deficient in an appreciation of the transverse and vertical flow structure that mediates shear stress for deep, narrow inner-channels, which often characterize large bedrock rivers. Here we present the detail of the structure of high Reynolds number flows for bedrock-controlled rapids of the Mekong River, SE Asia. Distinct filaments of high-velocity flow, separated by regions of slower flow, occur across channels; the numbers of filaments scale linearly with channel width to maximum-depth (B/hmax) ratios. Inner-channels with low ratios (B/hmax < 20) exhibit wall-effected flow structure. Effects include suppressed maximum velocity filaments due to: (i) significant channel-transverse flow; (ii) strongly-sheared vertical flow structure; and (iii) significant underflows. Such complex water column flow patterns largely defy theoretical description. Nonetheless near the bed, the vertical velocity distributions often conform to: (i) ‘law-of-the-wall’ logarithmic theory; or (ii) profiles in the near-bed region and within the transition to outer flow can be described using a log-wake function. Consequently, for selected velocity profiles it is possible to derive hydraulic parameters suitable for input to incision models. Chezy-C values are high, indicating low flow resistance, while bed shear stresses remain competent, even during low-discharges, to transport cobble bedload across low roughness bedrock surfaces. Thus, as competence is high, no blanketing sediment deposits can develop within inner channels to prevent bedrock erosion. Consequently, within similar high competence systems, incision is probably progressive as long as sediment supply is sustained to abrade the bedrock. The landscape modelling implication is that abrasion in this system is supply-limited and not limited by flow competence. In contrast, a transport-limited system is likely to evolve to exhibit an alluvial bed.