Rivers Case Studies/Examples

Kissimmee and Cockermouth Case Studies

Original length of Kissimmee River channel

103 miles

Size of Kissimmee River Floodplain

approximately 40000 acres and up to 3 miles wide

Reason for channelisation proposal

Prolonged flooding after hurricanes in 1940s impacted local towns

Project initiated in response to 1940s flooding

Central and Southern Florida Project, initiated by US Army Corps of Engineers

Floodplain species pre-channelisation

24 fish species, 4000-5000 waterfowl, alligators, much native wetland vegetation

Timeline for C-38 Canal

Between 1962 and 1971 the meandering river was straightened

C-38 Canal dimensions

56 miles, 27-91m wide, up to 10m deep

Flow controls installed in C-38

5 water control structures (similar to locks) installed

Main environmental impact of channelisation

Over 19500 acres wetlands lost

Decline in wildlife populations

Waterfowl populations dropped by 90%, bald eagles dropped by 70%, fish species dropped by over 50%

Impact on water quality

Increased pollutants and sediments due to disconnection to floodplain, oxygen levels dropped by 50% causing increased algal blooms

Cost of channelisation

Approximately $29 million USD

Restoration timeline

Grassroots efforts advocated before completion of channelisation, 1972 restoration discussions began, 1992 Water Resources Development Act, construction began in 1992, officially completed in 2021

Restoration project goals

Aimed to restore 44miles of meanders and 20000 acres of wetlands

Kissimmee restoration cost

Approximately $980 million USD

Environmental positives of restoration

Increase in dissolved oxygen, return of native vegetation, enhanced biodiversity, and re-establishment of natural hydrological patterns

Stakeholders for channelisation

USACE, Congress, SFWMD local residents, construction firms

Stakeholders against channelisation

FDEP, EPA, Audubon society, Friends of the Everglades, local residents

Cockermouth confluence

The River Cocker meets the River Derwent

Cockermouth cause of major flooding pre-management

Prolonged heavy rainfall led to high antecedent soil moisture - 1 in 1000 year rainfall event, and rapid run-off due to steep slopes and impermeable geology

Main features of Cockermouth 2009 flood

River rose by over 2.5m, PC Barker washed off a bridge, bridges washed away leading to major congestion, 1200 cut off from electricity, 20 schools closed, over 200 rescued.

Total damage cost of Cockermouth flood 2009

£276.5M GBP

Short-term response to 2009 Cockermouth flood

Met office extreme weather warning, residents protected their homes/evacuated, emergency relief centres set up, 200 people were rescued by emergency services

Medium-term response to Cockermouth 2009 flood

Building integrity assessments, electricity reconnection, and temporary housing, business premises and train stations built,

Cumbria Community Foundation actions

Fundraising appeal that raised £140000 in 48 hours

Political responses

Gordon Brown pledged £1M GBP funding, North West Development Agency pledged £1M GBP, farmers received additional grants to remove debris

Long-term responses to Cockermouth 2009 flood

17 of 20 bridges restored along with other infrastructure, insurance paid out (with large excesses), £4.4M GBP designated for future flood defences

Upstream works for flood defence in Cockermouth

Upstream storage improved to regulate flow into town - led to increased storage on floodplain around Bassenthwaite Lake

Soft engineering for flood defence in Cockermouth

River Derwent was dredged and embankments were built to increase channel capacity

Additional flood mitigation measure

Land use zoning stops new developments in high-risk areas

Hard engineering in Cockermouth for flood prevention

1.2km flood walls, 9 floodgates, and 120m self-raising barriers

Impact of Storm Desmond (2015) on Cockermouth defences

Floodwaters still exceeded defence capacity, flooding over 450 properties, but defences gave significant amount of time for residents to prepare and react

Maintenance concerns of flood defences in Cockermouth

2021 reports indicated flood defence damage from recent storms - concerns over sustainability of defences if not properly maintained