Figure 4.48 Streetlighting solution

In this scenario:

1. The open drains should be covered and enlarged when possible, for example outside of the UNESCO World

Heritage site boundaries. Inlet chambers are to be constructed at intervals along the roadsides to allow the entry of storm water. This will separate the surface water from black water which is currently discharged directly into the open drains;

2. Small-scale rainwater harvesting, such as stone or wooden water butts, are to be located to collect water from rooftops and to be collected by water butts for domestic use.

These can be made using local materials that are used within the Old Town such as quick lime, coral rag, squared hard wood beams of local species of hardwood135, and form a local business opportunity. These can also be made of recycled plastic and could provide a growing business area for the Flipflopi Foundation. See Figure 4.48;

3. Provision of pervious surfaces using natural stone. This can be laid on existing surfaces. It will improve uneven surfaces found on streets throughout the town. Additionally, it will reduce surface water runoff by providing surface water interception for small rainfall events;

4. At the back of the existing quayside seawall, a main surface water sewer interceptor, with gullies at frequent intervals can be tunnelled to intercept storm water within the drains.

The flow will then be pumped into a treatment feature, such as floating reedbeds/mangrove beds found at Wiyoni

Bay and along the sea wall before it discharges to the sea.

These can be integrated during the Corniche Path and quay wall upgrading project; and

5. In this scenario, all wastewater is to be collected separately and treated in the proposed STW as part of the wastewater masterplan.

135 UNESCO, Lamu Old Town Management Plan 2013-2017 (2013). Figure 4.48 Water butts made from different materials: natural stone, wood, recycled plastic

Source: Available at: 1) https://www.owlshall.co.uk/rainwaterharvesting/tanks/water-butts/stone-effect-300l/. 2) Norway, wood effect, Water Butt – 230 Litres – Freeflush Water Management Ltd. 3) Buy Cloudburst 200 litre Water Butt Kit | Evengreener.

Scenario 2: Combined system

If a separate system cannot be achieved in the short term, a combined conveyance system can be provided instead. The open drains would be covered and enlarged, when possible, to provide the hydraulic capacity needed to convey the combined flow. Inlet chambers are to be constructed at intervals along the roadsides to allow the entry of stormwater. A collection sewer connecting all existing outfalls can be installed under the sea front road or Corniche Path, which can then be reinstated to retain its current functions and importance to the local heritage. Archimedes screw pumps will be installed along the pipeline where required to improve flow transmission. Alternatively, a collection sewer could be built, attached to the sea wall and designed to incorporate existing jetties and other sea front activities. This can be explored as part of enhancement to the Corniche Path. This collector sewer fits into the future installation proposals of the existing wastewater masterplan.

The combined surface, grey and black water would be collected via sewer interceptor that takes the flow to a pre-treatment facility, such as septic tank/settling tank to collect the sludge, then the liquor can discharge to floating reedbed/mangrove beds for further treatment. This will prevent sedimentation and blockages from occurring and reduce maintenance required. In the long term, the sewer can be linked to the wastewater STW as proposed by the wastewater masterplan in order to eliminate the need for pre-treatment.

Location

The project is located within Lamu Town, specifically along the sea front road as due to the topography of the town all the water from the open drainage network flows west to east towards the Indian Ocean. The main collector pipe for wastewater will be sized to cater for a larger area to take into account future development and build capacity into the system.

> Lamu Town

Linkages

> There is a link with the existing wastewater masterplan from 2018; and > Links to project 9: Lamu Old Town waterfront improvement and town centre improvement and project 10: Wioni

Bay clean-up.

Table 4.37 Project 12 summary information

Sub-components Estimated cost (KES range) Benefits and impacts Financing options and delivery mechanisms Implementation agency and stakeholders

Feasibility study Covering of open drains.

Small scale rainwater harvesting Storm water interception drain along sea wall. Wastewater pipeline to treatment facility Floating reed/ mangrove beds at Wiyoni Bay and along the sea wall. Total cost = KES 264 million136

KES 60 million

The feasibility study will determine the cost for covering the open drains, harvesting rainwater and Construction of the storm water interception drain along the sea wall KES 60 million

KES 100 million Covering of the open street drains will help to separate the surface and grey/black water so that it can be redirected for further treatment

This will result in reduced risk of water borne diseases and improve the sanitation across the town as well as reduce the amount of waste water which is discharged into the Indian Ocean

Increased capacity in the drainage channels from the implementation of rainwater harvesting and separation of the surface and grey/black water will aid in building climate resilience into the drainage system The project will help improve drainage in Lamu Town helping to maintain its UNESCO World Heritage Site status and preserving its heritage Donors/IFI Potentially climate funds Implemented through the County/Municipality or LAWASCO as part of the wastewater masterplan Maintenance of the system should be undertaken by LAWASCO

Source: Atkins analysis Table 4.38 Project 12 basic analysis and timeline

Challenges

Lack of space along sea front road Design of roofs which could prevent implementation or efficient rainwater harvesting Detailed location and drawings of the drainage network within Lamu Town Medium to long-term The drainage masterplan needs to be developed and feasibility study to be completed, depending on scenario chosen work on the Lamu Town STW would need to be complete

Source: Atkins analysis Data gaps Time frame, key dependencies

136 A 20% buffer has been added to the total cost in order to account for the sensitivity of the UNESCO world heritage site and use of appropriate materials. SUED principles for implementation

Climate resilience recommendations

Flooding in Lamu Old Town is a significant problem, in particular when high tides combine with poor drainage as outlined above. Sea level rise and increases in heavy rainfall events will exacerbate the problem and are likely to lead to increases in flooding. The proposals for improved sewerage and drainage, including the potential use of SuDS and rainwater harvesting to reduce runoff, could significantly reduce flood risk, in particular, when implemented in combination with upgrades to coastal protection. The reduction in flooding would also Improve public health and reduce the prevalence of diarrheal disease, with associated health care cost reduction which is often a significant burden on low-income groups.

Social inclusion recommendations

This project has several socio-economic benefits. The improvement of drainage in Lamu Town will support the preservation of Lamu’s buildings and cultural heritage. The project will also increase water for domestic use, enhancing local water supply for household and ease the responsibility of fetching water for women by providing t readily available collected rainwater. It also creates a business opportunity for youth engaging in waste recycling and organisations such as Flipflopi and Taka Taka.

Covering the open water drain will also reduce the risk of water borne diseases and hence improve the health of the community thereby minimising healthcare costs.

To maximise the benefits of this project, it is recommended to sensitise local communities on proper ways of water harvesting and storage, and liaise with existing NGOs to provide training.

Case Study 4.21 - Stabilisation pond and reed bed137

At the Welcome Break Motorway Services in Oxford, UK a modified stabilisation pond and reed-bed system is used, in conjunction with a basic submerged aerated filter STW to treat the wastewater from the whole site. The plant produces high-quality effluent that meets the required discharge standards. The site has also become a wildlife haven and sanctuary, attracting birds, ducks, deer, butterflies and dragonflies.

137 Cress Water, Oxford motorway services (2021), Available at: https://cresswater.co.uk/case-studies/oxford-motorway-services/ (Accessed: 03/12/2021).

Case Study 4.22 - Central interceptor tunnel, tunnelling for a cleaner city - Auckland, New Zealand138

The older parts of central Auckland, New Zealand, are mainly served by old combined sewers, which drain wastewater from homes and business as well as stormwater collected from yards, rooftops and roads. Under storm conditions, this combined system exceeds its capacity and, as a result, overflows into waterways, polluting beaches and estuaries. With population growth and climate change increasing pressure on the combined sewer system, the situation had to be rectified. As part of a ten-year sewer and stormwater separation project to improve water quality, in 2019 a new wastewater interceptor was designed with planned construction completion in 2025. It will reduce overflows into waterways by 80%139, providing environmental, social and water quality improvements. At 14.7 km long, with an internal dimeter of 4.5 m, the central interceptor will be tunnelled using boring machines to divert combined sewerage flows from Lynn in Auckland to the Māngere Wastewater Treatment Plant.

138 Arup, Central Interceptor Tunnel (2021), Available at: https://www.arup.com/-/ media/arup/files/publications/t/the-arup-journal-2021-issue-1.pdf (Accessed: 03/12/2021). 139 NZherald, Central interceptor Auckland’s new 12 billion sewer tunnel to clean up z beaches (2019), Available at: https://www.nzherald.co.nz/nz/centralinterceptor-aucklands-new-12-billion-sewer-tunnel-to-clean-up-z beaches/

YMFKALHG2KI5WYSX24ZKFCF4XI/ (Accessed: 03/12/2021). Case Study 4.23 - Constructed Wetland with Mixed Mangrove and non-mangrove plants for municipal sewage treatment140

A constructed wetland wastewater treatment facility, with mixed mangrove and reed species, was successfully established in Shenzhen, China. The mixture of different plants was a key success factor as different species vary in terms of their respective pollutant removal efficiency. The effluent analysis indicated that the system was effective in removing pollutants including nitrogen, phosphorus, heavy metals and toxic organic pollutants. The removal efficiencies of nutrients and metals from the wastewater ranged from 75% to 98% and 88% to 96% respectively141 .

140 Nora F T, Yuk-shan W (2014), Constructed Wetland with Mixed Mangrove and

Non-mangrove Plants for Municipal Sewage Treatment, International Conference on Future Environment and Energy. 141 Prof. Nora, F T, Constructed Mangrove Wetlands for Wastewater Treatment (2016),

Available at: https://www.dsd.gov.hk/rdforum/2016/files/en/presentation/D1T2.pdf, (Accessed: 06/12/2021).