Watershed Hydrology: Go with the flow. Greg Jennings, PhD, PE

Transcription

1 Watershed Hydrology: Go with the flow Greg Jennings, PhD, PE

2 Streams What are your CHALLENGES? Hydrology too much water Pollutants upstream and on-site Vegetation wrong plants, wrong place Physical Constraints Conflicting Opinions Other?

3 What is a Stream? Body of water with a current, confined within a bed and streambanks Synonyms: brook, beck, burn, creek, crick, kill, lick, rill, river, syke, bayou, rivulet, run Streams are conduits in the water cycle and also important habitats Photo Credit: Eve Brantley, Auburn University

4 Streams are part of a watershed Area of land that drains water, sediment, and dissolved materials to a common outlet at some point along a stream Dunne and Leopold, 1978 Watersheds include: Land Water People Ecosystems

5 Watershed: a resource management unit

6 Kentucky Watersheds

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8 Hydrologic Cycle: Dynamic Equilibrium University of Central Florida

9 Hydrologic Cycle Flow of water through the earth s system, powered by gravity and solar energy 1. Precipitation 2. Evaporation 3. Evapotranspiration 4. Surface Runoff 5. Stream Flow 6. Infiltration 7. Subsurface Flow 8. Ground Water Flow

10 Fluvial Geomorphology: The study of landforms and fluvial processes Fluvial processes are associated with flowing water, including sediment erosion, transport, deposition

11 Fluvial Forms Bar Channel Confluence Cutoff channel Delta Floodplain Gorge Gully Meander Oxbow lake Pool Riffle Stream Valley Waterfall Watershed

12 Streams are Ecosystems Communities of organisms and their physical, chemical, and biological environments

13 Stream Ecosystems Channel (bed & banks) Floodplain Water & Sediment Plants & Animals Photo Credit: Eve Brantley, Auburn University

14 Stream Functions & Services 1. Transport water 2. Transport sediment 3. Habitat (aquatic & terrestrial) 4. Recreation & aesthetics 5. Safe Water Supply

15 Stream Impairment Causes (US EPA) 1. Pathogens 2. Sediment 3. Nutrients 4. Habitat Alterations 5. Organic Enrichment 6. Metals 7. PCBs 8. Temperature 9. Flow Alterations 10. Mercury

16 Effects of Urbanization on Streams (US EPA)

17 Urban Stream Syndrome (USS) Response to watershed changes Loss of natural functions & values Causes problems locally & downstream Requires systematic assessment & treatment

18 Symptoms of USS Erosion & incision Water quality decline Habitat loss Ecosystem degradation Flooding Land loss Infrastructure damage Recreation impaired Aesthetics impaired Economic loss

19 Urban Stream: Incision & bank erosion

20 Causes of USS Watershed impervious Channelization Impoundments Diversions Floodplain filling Pollution discharges Sedimentation Stormwater runoff Utilities & culverts Buffer loss Neglect & Ignorance

21 Urban Disturbances to Hydrologic Cycle University of Central Florida

22 Hydrograph Changes Due to Urbanization Urban Higher Peak Flow More Runoff Volume Flashier Response Lower Baseflow Rural

23 Runoff: more Infiltration: less Flooding: more Baseflow: less

24 Stream Condition Related to Impervious Surface Good Protected Fair Poor Impaired Degraded Urban Drainage Network Source: Center for Watershed Protection % Impervious

25 Constraints: Utilities, Road, Bridges, Culverts

26 Urban Stream Syndrome Run

27 Evidence of Neglect

28 What Makes a Stream Healthy? 1. Bed stability & diversity 2. Sediment transport balance 3. In-stream habitat & flow diversity 4. Bank stability (native plant roots) 5. Riparian buffer (streamside forest) 6. Active floodplain 7. Healthy watershed

29 Healthy Stream 1. Bed Stability & Diversity Appropriate size sediments to resist incision Open interstitial spaces to support habitats Riffle/Pool sequences in alluvial streams Step/Pool sequences in high-gradient streams

30 Riffles Steep slope High velocity & shear stress Large substrate High porosity & groundwater exchange Pools Flat slope Low velocity & shear stress Small substrate Scour during high flow

31 Problems: Bed Stability & Diversity Headcutting and excess scour Embedded gravels sealing off hyporheic connections Plane bed filling of pools Armoring

32 Healthy Stream 2. Sediment Transport Balance Minor erosion & deposition in balance long-term Alluvial bars and benches Upstream sources under control Sufficient stream power to avoid aggradation

33 Sediment Transport Flowing water does work: Erosion Transportation Deposition (of alluvium)

34 Problems: Sediment Transport Balance Excess stream power eroding bed Insufficient stream power aggradation Upstream sources inundating system

35 Streams convey water and sediment Lane s Balance (Lane, 1955) Channel Evolution Model (Schumm, 1984)

36 Healthy Stream 3. In-stream Habitat & Flow Diversity Macrohabitats: riffles, runs, pools, glides, steps, side channels, scour holes Microhabitats: roots, leaf packs, wood, rocks, plants, hyporheic zone

37 Hyporheic Zone

38 Riffle Pool Leaf Pack Undercut Banks Woody Debris

39 Problems: In-stream Habitats Uniform flow lack of diversity Lack of wood, leaves, roots, natural organics Human interventions Water quality impairments DO, nutrients, toxics

40 Healthy Stream 4. Bank Stability Dense native plant roots Low banks with low stress

41 Problems: Bank Stability Loss of vegetation High, steep banks channelization Armoring, invasive plants

42 Healthy Stream 5. Riparian Buffer (Streamside Forest) Diverse native plants with multiple layers Food and shade

43 Problems: Riparian Buffer Mowers and moo ers Invasive plants Armoring and impervious surfaces

44 Invasive, Nonnative Plants Tallow tree Japanese climbing fern Stilt grass (Microstegium) Wisteria Chinese privet Cogon grass

45 Healthy Stream 6. Active Floodplain Regular (every year) flooding to relieve stress Riparian forested wetlands Stormwater retention & treatment

46 Floodplain Functions Nutrient & Pollutant Processing Floodwater Storage Sediment Storage Channel Stability Habitat

47 Problems: Active Floodplain Channel incision Straightening, channelizing, levies Floodplain fill and encroachment

48 Healthy Stream 7. Healthy Watershed Stormwater management Wastewater management Upstream sediment control Watershed management

49 Problems: Healthy Watershed Stormwater energy and volume Point and nonpoint source pollution Erosion and sediment Stream neglect

50 Problems: Healthy Watershed Stormwater energy and volume Point and nonpoint source pollution Erosion and sediment

51 Stream Solutions Vision Innovation Creativity Teamwork Organization Responsibility You

52 "The oldest task in human history: to live on a piece of land without spoiling it" Aldo Leopold