Exeter 9 th ctober2014 Safe amp SuRe Urban Drainage Global resilience analysis of urban drainage systems A case study of Nakivubo catchment in Kampala city Seith Mugume snm205exeteracuk ID: 1026825
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2. Steering Group Meeting No. 3Exeter, 9th ctober2014Safe & SuRe: Urban DrainageGlobal resilience analysis of urban drainage systems:A case study of Nakivubo catchment in Kampala citySeith Mugumesnm205@exeter.ac.uk
3. Presentation outlineIntroductionResilience dimensions and scales Adaptation focused global resilience analysisModelling of Nakivubo urban drainage system in Kampala CityResults and discussionScenario 1 (Functional failure): Extreme rainfallScenario 2 (Structural failure): Cumulative pipe failureLife cycle cost analysisConclusions and future work
4. IntroductionImpact of emerging threats on existing urban drainage systems (UDSs) could lead to increased potential for pluvial flooding in cities and urban areasBuilding resilience in UDSs key to maintaining acceptable customer service levels for flood protection.Resilience: the degree to which the system minimises level of service failure magnitude and duration over its design life when subject to exceptional conditions.Key challenge: Lack of guidelines or standards for building resilience in specific UWSs.Study focus: Testing of resilience characterisation methods and potential resilience-enhancing strategies.Pluvial flooding in the UK, Source: RAPIDS Project http://emps.exeter.ac.uk/engineering/research/cws/research/flood-risk/rapids.html29th July 2014 pipe burst on 29th July 2014 at University of California, LA, US. Source: http://www.cbsnews.com/news/los-angeles-california-hit-with-another-water-main-break/2010 flooding in Dhaka, Bangladesh, Source: http://www.ipsnews.net/2013/02/killer-heat-waves-and-floods-linked-to-climate-change/
5. Key definitions: Maksimovic et al. 2009Surface flooding: Excess overflow that occurs at a node due to exceedance of the conveyance capacity of the minor system (Rossman, 2010; Balmforth et al., 2006). Safety (Reliability): the degree to which the system minimises level of service failure frequency over its design life when subject to standard (design) loading.Resilience: the degree to which the system minimizes level of service failure magnitude and duration over its design life when subjected to exceptional conditions.
6. Resilience dimensions and scalesDimensionsScaleDiao (2014)Temporal?Gersonious et al. (2010)Spatial?
7. Safe& SuReUDSImpact - Level of service% of flooded nodesFlood volume (m3)Recovery time (hrs)Global Resilience analysis: Adaptation-focusedFailed statePerformance metricsDesired state:Resilient UDSPotential strategiesAdapted from Butler et. al. (2014); Johansson (2010); Mehaffy & Salingaros (2013)
8. Theoretical UDS performance curveInfluenced by system robustnessInfluenced by flexibilityLoss of functionalityResidual functionality =
9. Kampala City: Background9Kampala CityEconomic and political capital of UgandaPopulation (growth rate): 1.72 million (5.6%) (UBOS 2012)Gazetted city area: 195 km2 (Metropolitan City Area: 800 km2)Annual rainfall: 1292 mm Seasonal pattern: Bimodal peaks (Mar – May & Oct – Dec)Temporal pattern: Convective high intensity, short duration rainfall
10. Key threats leading to pluvial flooding
11. Urbanisation: 441% increase in built-up area (1989 – 2010)Vermeiren et al. 2012
12. Land-use – A tale of two ‘cities’Kololo – planned upscale residential areaNakasero – city centre (high rise buildings)High density residential area (semi-formal)Muyenga - Bukasa planned residential area coexisting with an informal settlement in the Nakivubo wetland (flood zone)Bwaise- Informal settlement in low lying flood prone areaBukoto – planned residential flats
13. Effect of climate change on Kampala rainfall13Figure 3: Observed extreme rainfall event on 25th June 2012 estimated future T = 5,10,25,50 & 100 yr events (CF = 1.33 – 2.38)Single eventsObserved average monthly rainfall (Annual total: 1292 mm)Figure 1: Average monthly rainfall for rain guage stations (a) Makerere (1993-2009) (b) Municipality (1942 – 1993) and (c) City hall (1963 – 1992)Figure 3: Monthly climate CFs Kampala for 2030, 2050 and 2080 against a control period of 1961-1990 (Range = 0.99 – 1.4) Data obtained from CSAG (2013).Monthly averages
14. Case study: Nakivubo urban drainage system14
15. Model build in SWMM v5.1DEM for NakivuboCompute PIMP(Maximised Likelihood Classification Method)Sub catchment delineation (Area, natural drainage lines, & points)Compute sub catchment parameters (slope, CW)Build urban drainage model in SWMMv5.1(Sub-catchements, links, nodes, tanks)Key data:Sub-catchments: 31Area: 27.93 km2Nodes: 81Links: 81
16. 1. Resilience to future extreme rainfall eventsPerformance metricsObs. (T2)Estimated future extreme events% IncreaseT5T10T25T50T100Flood Volume (x 103 m3) 729.4 1,190.1 1,581.2 2,081.4 2,458.6 2,854.8 61-270%Flood Duration (hrs) 0.701 0.779 0.779 0.782 0.805 0.827 20-50%% Flooded nodes70.4%77.8%84.0%90.1%93.8%95.1% 11-35%Operational resilience (Reso)0.8210.7590.7320.7080.6860.666(8-19%)
17. 2. Resilience to cumulative pipe failure(A)A – Existing UDS with no storage (BAU); B – 1 large centralised detention pond (CS) : 315,000 m3;C – 28 distributed storage tanks (DS) : 315,000 m3(B)(C)
18. Global resilience analysis: ResultsReduction in flood volumeCS: 6.3% [1.2 – 12.0%]Reduction in flood durationCS: -2.2% [-2.0 – -2.2%]Reduction in flood volumeCS: 4.8% [1.2– 12.0%]DS: 31.0% [31.0 – 31.1%]Reduction in flood durationCS: -2.2% [-2.0 – -2.2%]DS: 26.1% [23.4 – 28.4%]Reduction in flooded nodesCS: 7.5% [3.5 – 10.0%]Reduction in no. flooded nodesCS: 7.5% [3.5 – 10.0%]DS: 22.4% [13.2 – 28.4%]
19. Resilience to cumulative pipe failureIncrease in ResilienceCS: 2.7% [-0.9 – 5.6%]DS: 34.3% [25.1 – 45.6%]
20. (A)(C)Cost analysis: synthetic storm sewer networkA – UDS with no storage (BAU); B – UDS with a 7,500 m3 centralised storage tank (CS);C – UDS with nine 833.3 m3 with distributed storage tanks (DS)Mugume S.N., Diao K., Astaraie-Imani, M., Fu G., Farmani R & Butler, D (2014) Building resilience in urban water systems for sustainable cities of the future, IWA World Water Congress and Exhibition, Lisbon, 21-26th September 2014(B)
21. Cost analysis: Discounted total costsHigher capital costs for CS & DS strategies => cost of storage devices. Reduction of 14.5% and 39.2% in total costs for CS & DS strategiesDiscounted total costs over 50 year design lifeIncludes direct tangible flooding costs
22. ConclusionsResilience defined as the degree to which the system minimises level of service failure magnitude and duration over its design life when subject to exceptional conditions.Global resilience analysis: promising methodology to test potential adaptation strategies to both functional and structural failure scenariosEmbedding redundancy and flexibility in UDS design or retrofit increases resilience to cumulative pipe failure scenariosReduction in total flood volume, mean flood duration and % flooded nodesCentralised storage strategy (B): 4.8%, -2.2% and & 7.5% Distributed storage design strategy (C): 30.1%, 26.1% and 22.4%Resilient design strategies more cost effective over the design life of UDSs.Future work:Carry out local resilience analysis to investigate system degradation and recovery behaviourInvestigate additional resilience strategies: e.g. rainwater harvesting
23. A vision for Kampala City of the Future?Source: http://richardmusinguziart.blogspot.co.uk/2013/07/future-visions-of-kampala-as.html
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