Academic journal article Theoretical and Empirical Researches in Urban Management

Hydrological Impacts of Urban Developments: Modelling and Decision-Making Concepts

Academic journal article Theoretical and Empirical Researches in Urban Management

Hydrological Impacts of Urban Developments: Modelling and Decision-Making Concepts

Article excerpt

1. INTRODUCTION

The urban sprawl preconises a wide and diffuse range of impacts. One of the main causes is the lack of integrated urban and water resource planning. The hydrological cycle for natural and urban catchments are significantly different. Vegetated areas are replaced by urban infrastructure, increasing the imperviousness, and decreasing both the transpiration and the infiltration processes (Mulligan & Crampton 2005). Runoff becomes more intense, and surfaces start pooling stormwater. A higher amount of sediments is brought to rivers, potentializing the risk of water supply contamination and the dissemination of diseases (Gaffield et al. 2003). Discharge flows are also intensified, and due to the sedimentation of river banks, the flood susceptibility increases, especially in low-lying regions, where the drainage condition is naturally problematic (Figure 1).

In coastal cities, heavy rainfalls are not the only phenomena to affect the hydrological behaviour of a basin. The tide variation aggravates the impact of flooding, as the water can only be routed throughout the river when the tide level is low. Lately, the situation is reckoned to be more hazardous as a consequence of climate change and sea-level rise (Shahapure et al. 2011).

Structural measures are required to improve drainage and control floods in urban watersheds (Yfantidou & Anthopoulos 2017). Rivers are regularly straightened in order to amplify their drainage capacity, causing a sequence of inundation problems when underestimated (Shahapure et al. 2011). The combined effects of reduced sinuosity, lower roughness, lower friction in the bank, and heavier runoff make a more intense amount of water to flow in a faster pattern through the channels, contrasting from the original and "natural" river conditions (Shahapure et al. 2011).

Indeed, many non-structured regions start developing their premises following chaotic outlines, driven by economic aspects, not socially or environmentally aware of the population welfare and local vulnerability. Thus, the environmental tools tend to be ineffective without the integration of urban planning and water resource management bodies (Seller 2014).

Moreover, the sustainable development of a new urbanised area depends on a successfully integrated water resource and urban planning management, involving the micro and macro drainage design, and the structural control measures towards water contamination and floods. Knowledge about the catchment hydrological behaviour is a vital element but depends on the development of studies. For that, investments are needed to raise modelling parameters and predict the hydrological impacts of forthcoming urban developments.

2. ENVIRONMENTAL TOOLS: APPLICABILITY AND EFFICACY

An effective water resources management is expected to be decentralised and represented by the public, private and community sectors (Pimentel da Silva 2010). A common purpose has to be established to keep or improve the watershed conditions for future generations, particularly concerning water quality and the population resilience and adaptation to hydrological hazard events (Pimentel da Silva 2010, United Nations International Strategy for Disaster Reduction - UNISDR 2015). Therefore, the institutionalisation of the environmental assessment tools results in a hazardous urban planning, which causes severe social and environmental vulnerability. Once the economic aspects dominate the urbanisation process, the deliberation of political actions tends to be unsatisfactory for the population welfare (Seller 2014).

The basic concepts for the Environmental Impact Assessment (EIA) rely on auditing the local environmental vulnerability, to promote alternative actions and minimise the predicted problems. The City Master Plan of every municipality is a basic environmental management tool that determines the local land use and possible activities to be implemented in each urban zone. …

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