title: Flood protection based on historical records is flawed – we need a risk model fit for climate change

authors: Fu, Xinyu

abstract: Flood-related disasters are on the rise, exacerbated by the worsening climate crisis, despite substantial investments in protective measures. Recent extreme weather events have demonstrated that even areas considered relatively safe can be susceptible to flooding. This calls into question the adequacy of our existing flood management strategies.

Historically, flood management has focused heavily on constructing higher levees and expanding drainage systems. While these measures contain water effectively most of the time, they can lead to catastrophic floods when they exceed their original design capacity. Moreover, they operate under the flawed assumption that future flooding can be reliably predicted based on historical flood data. This false sense of security encourages development in flood-prone regions.

The increasing unpredictability of rainfall patterns and intensities due to climate change has rendered these historical design assumptions inadequate. As a result, a significant "residual risk" persists, even after infrastructure improvements and plans for future enhancements.

To illustrate this, consider wearing a seatbelt while driving. The seatbelt reduces harm in the event of an accident but doesn't guarantee complete protection from injury. Now imagine road conditions deteriorating, weather becoming more unpredictable, and traffic volumes increasing. Some might opt not to drive due to the heightened risk, but for those already on the road, it's too late. This parallels how many countries continue to manage floods—often by constructing higher levees or larger drainage systems. However, this incremental development often lacks the strategic investment and infrastructure capacity required to safely manage excess water volumes during failures.

While housing development is essential, current flood risk assessments often neglect both current and future flood risk. Planning controls and additional infrastructure costs are frequently criticized as "red tape," further increasing residual risk. Recent weather-related disasters, such as Cyclone Gabrielle in New Zealand and wildfires in the northern hemisphere, have underscored the need to understand and manage residual risk. However, the recognition and incorporation of residual risk management in planning policies vary from one country to another, with many lacking clear national directives.

In New Zealand, for instance, there is limited national-level guidance on flood risk management. Still, flood risk professionals are increasingly aware of the rising residual flood risk, primarily due to climate change and continued development in flood-prone regions designated as "protected." There is consensus that current flood risk management practices need improvement.

Overcoming these challenges requires acknowledging and managing the growing residual risk linked to climate change. A more informed approach involves implementing robust guidelines against ill-advised development in flood-prone areas unless accompanied by infrastructure investments that reduce residual risk. Resilience-building measures, such as creating "sponge cities" and increasing space for water in flood risk management, are gaining traction. To break the cycle of disaster recovery and financial losses, planning must prioritize residual risk considerations in response to more frequent flooding and inevitable infrastructure failures.

text: Flood protection based on historical records is flawed – we need a risk model fit for climate change Flood-related disasters are on the rise, exacerbated by the worsening climate crisis, despite substantial investments in protective measures. Recent extreme weather events have demonstrated that even areas considered relatively safe can be susceptible to flooding. This calls into question the adequacy of our existing flood management strategies.

Historically, flood management has focused heavily on constructing higher levees and expanding drainage systems. While these measures contain water effectively most of the time, they can lead to catastrophic floods when they exceed their original design capacity. Moreover, they operate under the flawed assumption that future flooding can be reliably predicted based on historical flood data. This false sense of security encourages development in flood-prone regions.

The increasing unpredictability of rainfall patterns and intensities due to climate change has rendered these historical design assumptions inadequate. As a result, a significant "residual risk" persists, even after infrastructure improvements and plans for future enhancements.

To illustrate this, consider wearing a seatbelt while driving. The seatbelt reduces harm in the event of an accident but doesn't guarantee complete protection from injury. Now imagine road conditions deteriorating, weather becoming more unpredictable, and traffic volumes increasing. Some might opt not to drive due to the heightened risk, but for those already on the road, it's too late. This parallels how many countries continue to manage floods—often by constructing higher levees or larger drainage systems. However, this incremental development often lacks the strategic investment and infrastructure capacity required to safely manage excess water volumes during failures.

While housing development is essential, current flood risk assessments often neglect both current and future flood risk. Planning controls and additional infrastructure costs are frequently criticized as "red tape," further increasing residual risk. Recent weather-related disasters, such as Cyclone Gabrielle in New Zealand and wildfires in the northern hemisphere, have underscored the need to understand and manage residual risk. However, the recognition and incorporation of residual risk management in planning policies vary from one country to another, with many lacking clear national directives.

In New Zealand, for instance, there is limited national-level guidance on flood risk management. Still, flood risk professionals are increasingly aware of the rising residual flood risk, primarily due to climate change and continued development in flood-prone regions designated as "protected." There is consensus that current flood risk management practices need improvement.

Overcoming these challenges requires acknowledging and managing the growing residual risk linked to climate change. A more informed approach involves implementing robust guidelines against ill-advised development in flood-prone areas unless accompanied by infrastructure investments that reduce residual risk. Resilience-building measures, such as creating "sponge cities" and increasing space for water in flood risk management, are gaining traction. To break the cycle of disaster recovery and financial losses, planning must prioritize residual risk considerations in response to more frequent flooding and inevitable infrastructure failures.

year: 2023-08-31

title: Effects of low tide rainfall on the erodibility of intertidal cohesive sediments

authors: Pilditch, Conrad A.

subjects: sediment transport

abstract: Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min⁻¹ for 6 min) and low (0.36 mm min⁻¹ for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s⁻¹ (ME-30, g m⁻²) and critical erosion velocity (Ucrit, m s⁻¹)) were determined in annular flumes (bed area=0.17 m²). Ambient/control sediment erodibility in May (ME-30=211 g m⁻², Ucrit=0.18 m s⁻¹) was higher than in August (ME-30=30 g m⁻², Ucrit=0.26 m s⁻¹) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m⁻²) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm⁻²). In contrast, in August H. ulvae densities were low (52 ind. m⁻²) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm⁻²). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in Ucrit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, Ucrit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability

text: Effects of low tide rainfall on the erodibility of intertidal cohesive sediments Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min⁻¹ for 6 min) and low (0.36 mm min⁻¹ for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s⁻¹ (ME-30, g m⁻²) and critical erosion velocity (Ucrit, m s⁻¹)) were determined in annular flumes (bed area=0.17 m²). Ambient/control sediment erodibility in May (ME-30=211 g m⁻², Ucrit=0.18 m s⁻¹) was higher than in August (ME-30=30 g m⁻², Ucrit=0.26 m s⁻¹) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m⁻²) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm⁻²). In contrast, in August H. ulvae densities were low (52 ind. m⁻²) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm⁻²). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in Ucrit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, Ucrit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability

year: 2008

title: Whakahokia te reo ki tōna taioretanga: He rautaki reo mō Waikato-Tainui

authors: Roa, Raukura

subjects: Whakaora reo

abstract: Ko te kaupapa o tēnei pepa, ko te whakatakoto i tētehi mahere rautaki hei whakakaha, hei whakapakari i te reo Māori o te iwi o Waikato-Tainui. Ehara tēnei i te pepa wetewete i te rautaki whakaora reo, ehara hoki i te pepa tātari i ngā rautaki whakaora reo o te ao. Engari ia, he pepa whakatakoto i ōku whakaaro mō tētehi huarahi e ora ai te reo o Waikato-Tainui. Kei te rārangi whakapuakanga ētehi rauemi i toro atu ai au, heoi, kāore i āta tātarihia mō tēnei pepa. Nō reira, e rima ngā wāhanga o tēnei pepa. Ko te wāhanga tuatahi, he whakakaupapa i tēnei rautaki. Ko te wāhanga tuarua, he whakamārama i ngā whakahaeretanga o te iwi. Ko te wāhanga tuatoru, he whakatakoto i ngā whāinga o te rautaki. Ko te wāhanga tuawhā, he whakatakoto i te mahere e tutuki ai ngā whāinga o te rautaki. Ka mutu he whakatakoto whakaaro atu anō kāore i whakauru ki roto i te rautaki.

text: Whakahokia te reo ki tōna taioretanga: He rautaki reo mō Waikato-Tainui Ko te kaupapa o tēnei pepa, ko te whakatakoto i tētehi mahere rautaki hei whakakaha, hei whakapakari i te reo Māori o te iwi o Waikato-Tainui. Ehara tēnei i te pepa wetewete i te rautaki whakaora reo, ehara hoki i te pepa tātari i ngā rautaki whakaora reo o te ao. Engari ia, he pepa whakatakoto i ōku whakaaro mō tētehi huarahi e ora ai te reo o Waikato-Tainui. Kei te rārangi whakapuakanga ētehi rauemi i toro atu ai au, heoi, kāore i āta tātarihia mō tēnei pepa. Nō reira, e rima ngā wāhanga o tēnei pepa. Ko te wāhanga tuatahi, he whakakaupapa i tēnei rautaki. Ko te wāhanga tuarua, he whakamārama i ngā whakahaeretanga o te iwi. Ko te wāhanga tuatoru, he whakatakoto i ngā whāinga o te rautaki. Ko te wāhanga tuawhā, he whakatakoto i te mahere e tutuki ai ngā whāinga o te rautaki. Ka mutu he whakatakoto whakaaro atu anō kāore i whakauru ki roto i te rautaki.

year: 2011