Monitoring Headwater Streams for Landscape Response to

Transcription

1 Monitoring Headwater Streams for Landscape Response to Climate Change Matthew Connor, PhD Connor nvironmental, nc. icom Healdsburg, California

2 verview Headwater stream geomorphology Response to hydrologic change Monitoring to detect change ffects of land management ffects of climate change

3 Headwater Streams as ndicators of Change Dietrich and Dunne, 1993 The Channel Head, N Channel Network Hydrology (ds., Bevin and Kirkby). nstability at channel heads can generate destructive debris flows or gullying, and heavy sediment loading downstream. Because the channel-head location at any time is controlled by the relative magnitudes of sediment supply and the erosion potential due to runoff, fluctuations in climate or land use, which alter runoff rates, surface erodibility and sediment supply, cause shifts in channel head location. Therefore, the channel head may be the element of the coupled hillslope-channel system that is most sensitive to changes in external factors. rosion and deposition cycles which sweep through drainage basins may be largely influenced by shifts in the balance controlling channel-head locations

4 Headwater Stream Geomorphology Swale/zero order basin No surface channel Topographic convergence Subsurface flow accumulation Colluvial soil

5 The Channel Head Slopes < 45 degrees Defined banks Soil mantle 1 to 5 ft thick Subsurface flow di drives erosion ften discontinuous with vegetated steps Springs in wetter regions

6 Headwater Stream Geomorphology Discontinuous or intermittent surface channel Soil or organic substrate Minimal channel erosion Topographic convergence with lateral soil creep

7 Headwater Stream Geomorphology First order channel Substantial fluvial erosion Resistant channel substrate Gravel Bedrock Woody debris Bank erosion

8 Headwater Stream Geomorphology Debris flow originating in colluvium-filled bedrock hollow Steep slope gradient Colluvial soil accumulation to some critical depth Triggered by hydrologic forcing (typically an extreme storm or flood)

9 Headwater Stream Response Changes in flow Peak runoff Annual runoff Seasonal flow ncrease or decrease in flow rosion processes Surface flow surface erosion or mass failure of undermined steps at plunge pools Subsurface flow seepage erosion Landsliding

10 Headwater Stream Response Response to land management Urban development Forest canopy removal Timber harvest Conversion to agriculture ncreases in peak flow

11 Headwater Stream Response Forest canopy removal 20 to 30% increase in peak flow in coastal redwoods in northern California ncrease in annual runoff xpect variation among ecosystems Anticipated channel response Headward erosion at channel head Accelerated channel and bank erosion Rates uncertain

12 Monitoring Headwater Streams- Topographic Survey Channel response may be subtle in short term Natural variability Change expressed over time-years or decades? Response to hydrologic events Approaches to detection and measurement of change Detailed topographic surveys xtensive channel surveys

13 Monitoring Topographic Change Cross-section section surveys Swale Channel head zone Channel Longitudinal profile survey riented to detecting vertical change in channel bed as well as channel extension

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16 xtensive Channel Surveys Combine with detailed topographic surveys in a 2-stage sampling design Map channel heads Watershed scale Regional scale Describe location of channel heads and process changes that may occur

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18 xtensive Channel Surveys Resources GPS survey equipment LiDAR topographic p mapping Robust statistical methods (e.g. GLM s capable of evaluating potential covariates) Locate, describe and identify channel heads Monitor to observe horizontal change in channel position ther hydrologic and ecosystem parameters

19 Analytical Approaches xtensive regional data sets Reveal differences in xisting conditions Response to change xample Slope drainage area relationship Drainage Area Area Acres Unchanneled Slope Landslide Channeled Colluvium Landslide Residual Soils Slope %

20 Application to Climate and Hydrologic Change in Alaska Direct measurement of physical change Sensitive to change Complements other data sets and models Regional differences Boreal forest (drier?) v. coastal forests (wetter?) Channel response in permafrost Network extension, soil drainage Vegetation response Wetter v. drier Accelerated growth Fire