1 / 17

Discharge-Area Relations from Selected Drainages on the Colorado Plateau: a GIS Application

Discharge-Area Relations from Selected Drainages on the Colorado Plateau: a GIS Application. GISWR Term Project By W. Scott Cragun. Outline Problem to be addressed Part I Methods Results Conclusions Part II Methods Results Conclusions.

dblackwell
Download Presentation

Discharge-Area Relations from Selected Drainages on the Colorado Plateau: a GIS Application

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Discharge-Area Relations from Selected Drainages on the Colorado Plateau: a GIS Application GISWR Term Project By W. Scott Cragun

  2. Outline • Problem to be addressed • Part I • Methods • Results • Conclusions • Part II • Methods • Results • Conclusions

  3. Problem to be addressed: • A is often substituted for Q in fluvial models • Example: Family of equations knows as Stream Power Laws • Used to: • model aggradation / incision within rivers • model incision rates within rivers • Basic Equations: Z = kQmSn OR Z = kAmSn • k is proportionality constant • Q is discharge • S is slope • m/n are exponents whose values are debated • A is drainage area

  4. Commonly held that: • Q = bAc; A is the contributing drainage area • b is a proportionality constant • c is a scaling exponent (1 is most common value) • Most commonly a linear (or nearly linear) relation • Perhaps true for alluvial rivers in humid climatic zones • What about for mixed alluvial-bedrock rivers in semi-arid climatic zones?? From: Mitchell, D.K., 2000

  5. Part I - What I’ve Done: • Six river basins selected • Gunnison River • Upper Colorado River • San Juan River • Paria River • Little Colorado River • Fremont/Dirty Devil River • Encompass the southern/arid basins and the northern/relatively wetter basins

  6. Part I - What I’ve Done: • The raw DEM’s • DEM’s downloaded from USGS seamless data • (http://seamless.usgs.gov/) • 30m DEM projected in UTM and interpolated at 100m cell size • Run TauDEM tools in order to determine flow direction and flow accumulation Upper Colorado Fremont Gunnison Paria San Juan Little Colorado

  7. Part I - What I’ve Done: • Obtain USGS gaging station data for each of the 6 drainages • (http://waterdata.usgs.gov) • Mean annual flow • Mean peak flow • 35 total gaging stations • Import gage location in GIS • Manually extract contributing area at each • gaging station • compare GIS contributing area to USGS drainage area • plot discharge against contributing drainage area Little Colorado River

  8. Part I - Results: • Significantly more scatter in the data from the • Colorado Plateau Y = 0.08A0.95 R2 = 0.82

  9. Part I - Results: • Individual basins show unique downstream discharge patterns

  10. Part I - Results: • Hydrographs show peak runoff during - spring (snow melt) : northern drainages • - fall (monsoon) : southern drainages northern drainages southern drainages

  11. Part I - Results: • However… Individual basins show: 1) grouping of 3 northern basins • 2) unique relations in southern 3 basins

  12. Part I - Results: • Splitting drainage basins into two groups…

  13. Part I - Conclusions: 1) Close Q-A relation in northern drainages But… scaling exponent (c) is not nearly 1 : value is 0.70 - suggests that streams in humid environments are capable of generating greater discharges per unit drainage area than in arid and semi-arid regions 2) Large scatter in Q-A relation in southern drainages (lower r2) Suggests that - geologic controls influence discharge generation - climatic influence = greater evaporation 3) Discharge generation per unit area varies between all 6 basins 4) Streams in ARID regions: appropriate Q-A relation should be carefully chosen even when significant water is available

  14. Part II - What I’ve Done: • Obtain precipitation data for western US from PRISM • (http://www.wcc.nrcs.usda.gov/climate/prism.html) • clipped out for each drainage • resampled at 1000 m cell size • Can RUNOFF be predicted from PRECIPITATION ?? • runoff coefficients estimated for each basin From: http://www.dot.ca.gov/hq/oppd/hdm/pdf/chp0810.pdf

  15. Part II - Results: • Initial runoff coefficients too high • Readjusted to better predict runoff

  16. Part II - Results: • First attempt to define precipitation-runoff relation through regression failed • Try, try again… San Juan shaded relief map San Juan precipitation map

  17. Part II - Conclusions: • Estimated runoff coefficients vary widely between 6 basins • 0.0084 to 0.30 • Suggests that - local climate conditions influence discharge • monsoon vs. snow melt • - local geologic characteristics influence discharge • - local soil and vegetation distribution affects discharge • 2) Runoff prediction from precipitation is not perfect • oversimplified • 3) Need a more robust coverage of drainage characteristics to establish • representative discharge – precipitation relations in each basin

More Related