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Flooding in New Zealand Report

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Updated: Dec 12th, 2019


Floods are the most common natural disasters that New Zealand has been experiencing for centuries. Given that New Zealand is an island, it experiences floods such as coastal floods, flash floods, rainfall floods, and riverine floods. These floods have catastrophic impact on human settlements and the environment, and thus cause huge economic losses.

Rouse (2012) states that, about two-third of population in New Zealand live in areas that are susceptible to flooding. This means that over a million of people experience floods in New Zealand. Hence, there is a need to design appropriate solution that would mitigate the impact of floods or control them so that they could have minimal impact on human settlements and the environment.

Evidently, the government of New Zealand has employed a number of strategies to control floods or mitigate their impact, which include creation of dams, afforestation, and construction of dikes. Therefore, this report examines structural interventions and modifications as effective solutions to the perennial floods that cause havoc in New Zealand.

Structural Interventions

Construction of the embankments is a structural intervention that is effective in controlling and mitigating the impacts of floods. The embankments are suitable in preventing riverine floods, which usually occur due to overspill of the water that flow in rivers (Smart & McKerchar 2010). When it rains, water flow into rivers, and hence, make them swell and flood their banks.

Since rivers are small, excess floods from highlands make rivers to overflow and consequently cause floods in their banks and surrounding environments. Moreover, in rivers that flow through plains, excess water overflow and cause floods in the plains. Human settlements that are around the banks and plains usually experience floods that overflow from swollen rivers due to flash floods.

In this view, to control such flooding, construction of embankments is an effective solution. Attz and Marchand (2005) recommend that the height of embankments constructed along rivers should be greater than the maximum level of water to prevent water from overflowing and flooding riverbanks.

Therefore, construction of embankments is necessary to control floods that emanate from rivers and cause havoc on human settlements around the riverbanks and plains.

Construction of dams is another structural intervention that is effective in controlling floods. Given that floods normally occur when rivers burst their banks, construction of dams along rivers is essential. Dams act as buffering points, which store excess water while maintaining the normal flow of water in the river.

Dams provide structural measures of controlling floods because they have the capacity to handle huge volumes of waters, which usually cause flooding if they flow freely without any control measure (European Working Group on Dams and Floods 2010). Many dams that are common in Europe are important because one of their purposes is to control floods.

Essentially, dams are important in controlling floods in the plains where human settlements and arable land exist. In the construction of dams, engineers need to consider the amount of water that flow in the river during the rainy seasons and the dry seasons. Seasonal variation of water in the river is important as it determines the design and the capacity of a dam.

Rouse (2012) explains that engineers determine probable maximum flood when constructing dams that control floods. The determination of the probable maximum flood is critical as it enhances the capacity of a dam to control floods when rivers overflow. Thus, to control floods along the rivers of New Zealand, construction of dams is necessary.

Structural Modifications

Dredging is a structural modification method of controlling the occurrence of floods. Given that obstructions that occur in rivers cause floods, expansion of rivers in terms of the depth and breadth enhances their capacity to handle excess water during rainy seasons.

During heavy rain, floods carry with them boulders and debris materials, which gradually accumulate in the riverbed, reduce the capacity of the river, and eventually obstruct the flow of water. Consequently, the reduced capacity of the river and obstruction by boulders increase the occurrence riverine floods. Rouse (2012) asserts that an understanding of the geomorphology of rivers is central in controlling floods.

In this view, the sedimentation of debris materials and the accumulation of boulders are geomorphologic factors that contribute to the occurrence of floods. According to Macklin and Lewin (2003), the accumulation of sediments due to increased surface runoff from arable fields has made rivers to be susceptible to flooding.

Debris materials and boulders reduce the capacity of rivers and obstruct the flow of water in rivers that are in New Zealand, and thus contribute to the occurrence of perennial floods. Hence, to prevent and control floods caused by sediments and boulders that obstruct the flow of water in rivers, dredging is necessary.

Improvement of the drainage systems is another structural modification strategy of controlling floods. Human settlements and structures cause floods because they enhance the occurrence of surface runoff. Surface runoff is water that accumulates on the surface because they are unable to infiltrate quickly into the soil (Caruso, Ross, Shuker, & Davies 2013).

In a natural environment, surface runoff rarely occurs because rainwater percolates into the soil very fast, and thus water does not get an opportunity to form surface runoff. Human settlements and other structures reduce the capacity of the soil to absorb water during rain, which causes water to accumulate on the surface and move as surface runoff.

In settlements where there are poor drainage systems, storm water accumulates and causes floods. According to Hudson and Harding (2004), the nature of culverts, weirs, and floodgates determines the occurrence of floods in an urban environment. Poor drainage usually occurs when culverts, weirs, and floodgates have inappropriate design or poor maintenance.

Specifically, inappropriate design and poor maintenance of drainage systems reduce the hydraulic capacity of the drainage systems in urban environment, and consequently contribute to flooding. Thus, urban environment that is full of human settlements require well-designed drainage systems that are under regular maintenance to optimize their buffering capacity.


The torrential rainfall, human activities, and landscape are common factors that contribute to the occurrence of floods in New Zealand. Floods usually cause huge losses as they destroy property and threaten the lives of many people. A significant number of people in New Zealand experience floods as about a third of them live in areas that are susceptible to flooding.

Since floods are natural disasters, there are several strategies for mitigating their impacts or controlling their occurrence. Structural interventions form an effective solution of mitigating the impacts of floods and controlling their occurrence in New Zealand.

Construction of embankments and dams along rivers are important interventions because they buffer the flow rate of water in rivers. Moreover, dredging of rivers to remove sediments and boulders enhances the capacity of rivers to handle huge volume of water during rainy seasons. Ultimately, improvement of drainage systems in urban settlements is critical in controlling the flow of water.


Attz, M., & Marchand, M., 2005. Flood and Storm Control. Web.

European Working Group on Dams and Floods 2010. Dams and Floods in Europe: Role of Dams in Flood Mitigation. Web.

Caruso, B., Ross, A., Shuker, C., & Davies, T., 2013. ‘Flood Hydraulics and Impacts on Invasive Vegetation in a Braided River Floodplain, New Zealand.’ Environmental and Natural Resources Research, vol. 3. no.1, pp. 92-110.

Hudson, H., & Harding, J., 2004. Drainage Management in New Zealand. Web.

Rouse, H., 2012. . Web.

Macklin, M., & Lewin, J., 2003. ‘Rapid Communication: River Sediments, great floods, and centennial-scale Holocene climate change.’ Journal of Quaternary Science, vol.18. no. 2, pp. 101-105.

Smart, G., & McKerchar, A., 2010. ‘More flood disasters in New Zealand.’ Journal of Hydrology, vol. 49. no. 2, pp. 69-78.

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