Introduction to stream assessment

Transcription

1 Why do stream assessment? Introduction to stream assessment Given the current condition of rivers and the heightened public interest in them, there is a significant need for the ability to determine the health of streams. The current stability and functionality of the stream is an important consideration that should be addressed at the start of a restoration project. NRCS, In-stream modifications undertaken in the absence of a firm understanding of the hydrology and sediment transport, and resultant implications on channel form, can only lead to haphazard success at best, and may result in gross cannel instability and degradation that can adversely affect the entire drainage network. Stream channels alter their physical characteristics of channel geometry planform gradient base level in response to changes in flood characteristics and sediment supply USACE and USEPA. (2004) PHYSICAL STREAM ASSESSMENT: A Review of Selected Protocols for Use in the Clean Water Act Section 404 Program, 212 pp. Lane s (1955) description of equilibrium Shumm s (1969) model of channel change where Q = discharge, Qs = sediment load, W = width, D = depth, F = w/d ratio, λ= meander wavelength, s = slope, P = sinuosity where Q s = bed sediment load, D 50 = median bed sediment size, Q w = flow discharge, S = slope Thus, the bed sediment load is proportional to the available force Expected geomorphic response to an increase in Q and Qs increases in channel width, width/depth ratio (wide & shallow), meander wavelength; decrease in sinuosity; and an increase or decrease in depth and slope (FISRWG, 1998) (Fitzpatrick, 2001) 1

2 How much information (quantity, quality) you get on the physical variables will depend on the assessment used. Habitat assessments Stream classification Geomorphic reconnaissance assessments Multidisciplinary assessments Knowing the goals of the watershed management plan is key! (Fitzpatrick, 2001) Watershed Science Institute Technical Report (2001) Stream Corridor Inventory and Assessment Techniques A guide to site, project and landscape approaches suitable for local conservation programs Report outlines 34 different inventories/assessments i t See also: Fitzpatrick, F A comparison of multi-disciplinary methods for measuring physical conditions of streams. Pages 7-18 in Geomorphic Processes and Riverine Habitat, J. Dorava, D. Montgomery, B. Palscak, and F. Fitzpatrick (eds.), American Geophysical Union, Washington, D.C. Niezgoda, S.L. and Johnson, P.A Improving the urban stream restoration effort: identifying critical form and process relationships. Environmental Management 35(5): Includes information about the following for each technique: Primary setting e.g., floodplain, riparian area, water quality, aquatic habitat Sampling intensity it cursory/detailed d Required skill level, training, & time Kind inventory/assessment and qualitative/quantitative; Proximity onsite/remote Need for a reference site Suitability for monitoring methods 2

3 Basis of the USEPA Watershed Assessment of River Stability & Sediment Supply (WARSSS) The Stream Saver Time Magazine 2004 Levels I and II are used to classify stream types from (Rosgen, 1994) Level I: Geomorphic characterization Preliminary assessment using topo maps, air photos, GIS (Rosgen, 1994) Level II Start with A-G, then stream types are broken into discreet slope ranges and dominant channel-material particle sizes 42 major stream types More detailed assessment that requires some field work to measure specific channel dimensions Level II Level I Level II 3

4 Levels III and IV Natural Channel Design Methods describe the geomorphic condition of the stream identify geomorphic process relations Morphological descriptions & calculations are linked to channel stability and sensitivity to disturbance, sediment supply, etc. Field reconnaissance technique that assesses channel-floodplain conditions, riparian areas, water quality, and aquatic habitat Qualitative multidisciplinary assessment: Fluvial geomorphology channel conditions, bank stability, riparian zone, pools, riffle embeddedness Biology barriers to fish movement, pools, riffle embeddedness, instream fish cover, canopy cover Engineering channel conditions, bank stability Water quality nutrient enrichment, water appearance A healthy stream: complex ecosystem benefit from increased complexity & diversity in physical structure chemical pollution (BOD, N & K, ph) stream/floodplain connectivity Elements are assessed on a 1 to 10 scale as follows: < 6.0 = Poor = Fair = Good > 9.0 = Excellent Geomorphological river channel reconnaissance Site evaluations GIS-based data input and management Stability ranking 4

5 RGA field sheet used for initial site screening Additional hydrologic and sedimentary input variables needed: Flow-frequency curve Stage-discharge curve Sediment-rating curve Channel cross-section and gradient Bankfull flow capacity Channel Evolution Model (CEM) 5