Relation of In-stream Physical Heterogeneity and Ecological Quality: - PowerPoint PPT Presentation

DSD Research & Development Forum 2015 Session 2 – Revitalising Water Bodies Relation of In-stream Physical Heterogeneity and Ecological Quality: Implications to Sustainable ECO-Flood Channel Design Onyx WAI, P. I. Ayantha GOMES, Derek LAM and Sarah CHAN Department of Civil & Environmental Engineering The Hong Kong Polytechnic University

Contents 1. Introduction and Background 2. Methodology 3. Preliminary Results: Ecological Assessment (2014-2015) Physical Modelling (In-situ and Laboratory) 4. Summary and Future Work 2

Source: WWF Channel Rehabilitation: Cheonggyecheon, Korea Source: Schellack Cheonggyecheon restoration involved the rebuilding of a 10.9 km long waterway, replacing the heavily polluted gully covered under concrete highway. Construction took Before After place from 2002 to 2005, costing USD$281million. Source: madmarv00 Source: Bohyunlee Source: Erik Möller 3 Source: Source: stari4ek http://cheonggye.seoul.go.kr/

Channel Rehabilitation: Bishan-Ang Mo Kio Park and Kallang River, Singapore This is one of the flagship projects under Singapore’s ABC (Active, Beautiful and Clean) Waters Programme, which transformed the concreted Kallang River into a meandering, near-natural river crossing the entire park. Construction took Source: Atelier Dreiseitl place from 2009-2012, and the project budget was Euro € 39million. 4 Source: Atelier Dreiseitl Source: Atelier Dreiseitl

2015 Policy Address Water-friendly Culture and Activities We will adopt the concept of revitalising water bodies in large-scale drainage improvement works and planning drainage networks for NDAs (new development areas) so as to build a better environment for the public. (Paragraph 181) 5

The Ecology of Hong Kong and its Streams Conventional perception of Hong Kong…………. However, it has a variety of habitats: forests, waterfalls and streams, farms, etc… 6

Characteristics of Hong Kong streams  Steep and short (many without a distinctive middle course) (80 % of the annual rainfall)  Contrasting wet and dry seasons  Streams are densely distributed.  Several tributaries/sections are ephemeral.  Poor drainage during the dry season, specially the ones with discrete pools/flat terrains. 7

Status of Hong Kong streams, government policy and societal views  Former engineering practices advocated designs that minimize flood related hazards.  With the changes in socio-economic conditions, public tend to look for more natural looking waterways; DSD the custodian Yuen Long Main of most of the regulated lotic waters has taken the initiative Nullah (in total ~5 to incorporate eco-friendly features. (2015 Policy Address) km are like this; perhaps the best  For more ecological friendly features and sustainable river reference for a channel designs, new research is needed. hydraulically sound, but ecologically dead regulated lotic water in Hong Kong) Jordan Valley Ho Chung River Nullah (aesthetic fish ladder 8 uplift) (ecological uplift)

What’s the problem here? Two major interactive No flora/fauna, especially pathways (at least) are macroinvertebrates such disturbed: as shredders, grazers No lateral (stream-floodplain) No proper nutrient and vertical (stream-aquifer) decomposition along the connections stream Thus four dimensional Thus river continuum framework concept / concept doesn’t satisfy spatiotemporal hierarchy doesn’t satisfy No flow-landscape interaction No biodiversity in the No cycling of nutrients boundary of terrestrial even in the low flow and freshwater system hydrologic landscape No flora/fauna in both low/high flow flood Thus flood pulse plains concept doesn’t satisfy Thus boundary / interface perspective (concept) doesn’t satisfy Hydraulically excellent, Ecologically dead!!!! 9 Yuen Long Nullah

Restoration Concepts “The science and practice of river restoration” ( Wohl et al. 2015a)  Common restoration approaches  Structure-orientated approach: Restoration by engineering a river to an identified form that has been lost (e.g. meandering).  System function approach: Restoring a desired process in the river system, and the system is allowed to develop in response to the restoration.  Hybrid approach: Restoring a crucial element of the river’s structure and function (e.g. pool - riffle sequence), and the system is allowed to evolve. 10

Restoration Concepts Adaptive Management for River Restoration  Adaptive management a structured, iterative process of robust decision making to reducing uncertainty over time via system monitoring The Conservation Measures Partnership, 2013  Example: Sediment Regime  Major role in determining geomorphology, habitats, ecological disturbance regime, etc.  Water and sediment inputs are non-linear and episodic.  River response changes at different temporal and spatial scale.  Data of sediment regime (historical and present) are difficult to obtain.  Also influenced by human activities. 11 (Wohl et al. 2015b)

Restoration Goals Project Objectives Detailed stream eco-hydraulic assessment Maintain flood control function and sediment 1. balance, supply organic matters to downstream Design of the in-situ eco-channel model reaches; and laboratory physical model Establish appropriate pools, riffles, in-stream 2. covers and sediment which support If no Analysis using in-situ eco-channel, physical and macroinvertebrate and fish colonization; numerical models Establish appropriate controlled habitats for 3. If no submerged, floating and emergent flora; Is the ecological enhancement satisfactory? Enhance overall water quality, especially at the 4. If yes downstream reaches where anaerobic conditions exist; Is flood safety acceptable? Provide a basis for future rehabilitation work and 5. If yes prepare of guidelines. Actual rehabilitation work 12

Ecological Assessment  To understand the existing condition and site characteristics, and provide baseline information for future comparison. Twice every year dry season(Jan-Feb) wet season (Jul-Aug) Sampling sites (total 20 sites) A1-A10 (natural stream bed sections) D1-D10 (concreted channel sections) Measurements Physical / Chemical Biological Geomorphological benthic algae, pH, conductivity, submerged and floating flow depth, velocity, turbidity, DO, nitrite, plants, emergent plants, width, Froude number, nitrate, ammonia, riparian vegetation, fish, pool and riffle reactive phosphorous, avi-fauna, benthic distribution, etc. sulfate, sulfide, TS, TSS, macroinvertebrates, chlorophyll-a, etc. diatoms, etc. 13

Map of the 20 Sites (Downstream) (Upstream) 14

Sampling Sites A1-A10 (Natural Stream Bed) (A1) (A2) (A3) (A5) (A4) (A8) (A6) (A10) (A7) (A9) 15

Sampling Sites D1-D10 (Concreted Channel) (D1) (D2) (D3) (D5) (D4) (D7) (D10) (D9) (D8) (D6) 16

Water Quality Results (2014-2015 averaged)  Contrast between A-sites (natural bed, except A8) and D-sites (concreted channel sections)  Within the D-sites:  Less polluted: D6, D8, D9 and D10  More heavily polluted: D2, D4, D5, D7 17

Water Quality pH DO (mg/L) 10 10 15 -5 0 2 4 6 8 0 5 A1 A1 A2 A2 A3 A3 A4 A4 2014-15 Average 2014-15 Average A5 A5 A6 A6 DO(mg/L) A7 A7 A8 A8 DO(mg/L) pH A9 A9 pH A10 A10 D1 D1 D2 D2 D3 D3 D4 D4 D5 D5 D6 D6 D7 D7 D8 D8 D9 D9 D10 D10 Turbidity (NTU) Total Solid (mg/L) -10 10 20 30 40 50 60 0 -1000 1000 2000 3000 4000 A1 0 A2 A1 A3 A2 A4 2014-15 Average Turbidity (NTU) A3 Total Solid (mg/L) A5 2014-15 Average A4 A6 A5 A7 A6 TUR (NTU) A8 A7 A9 A8 A10 A9 TS D1 A10 D2 D1 D3 D2 D4 D3 D5 D4 D6 D5 D7 D6 D8 D7 D9 D8 D10 D9 D10 Conductivity (µS/cm) -1000 1000 2000 3000 Total Suspended Solid (mg/L) 0 -100 100 150 200 250 -50 A1 50 Total Suspended Solid (mg/L) 0 A2 A1 Conductivity (µS/cm) A3 A2 2014-15 Average A4 A3 2014-15 Average A5 A4 A6 A5 A7 A6 CON (µS/cm) A8 A7 A8 A9 TSS A9 A10 A10 D1 D1 D2 D2 D3 D3 D4 D4 D5 18 D5 D6 D6 D7 D7 D8 D8 D9 D9 D10 D10

Water Quality 2014-15 Average 2014-15 Average 2014-15 Average Nitrate-Nitrogen (mg/L) Nritrite-Nitrogen (mg/L) Ammoniacal-Nitrogen (mg/L) 15 25 30 20 25 10 NO3 (mg/L) NO2 (mg/L) NH3 (ng/L) 20 15 15 10 5 10 5 5 0 0 0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 -5 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 -5 -5 -10 NO3-N NO2-N NH3-N 2014-15 Average 2014-15 Average 2014-15 Average Sulfide (mg/L) Soluble Reactive Phosphorus Sulfate (mg/L) (mg/L) 0.4 50 0.3 30 40 S2 (mg/L) SO4 (mg/L) SRP (mg/L) 0.2 20 30 0.1 20 10 10 0 0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 A10 D10 0 A1 A2 A3 A4 A5 A6 A7 A8 A9 D1 D2 D3 D4 D5 D6 D7 D8 D9 -0.1 -10 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 -10 S2 SRP SO4 19

Water Quality 2014 2015 Dry Season Wet Season (Pollution becomes less serious) 20