Geomorphic modeling and routing improvements for gis based watershed assessment in arid regions
Download
1 / 28

Geomorphic Modeling and Routing Improvements for GIS-Based Watershed Assessment in Arid Regions - PowerPoint PPT Presentation


  • 118 Views
  • Uploaded on
  • Presentation posted in: General

Geomorphic Modeling and Routing Improvements for GIS-Based Watershed Assessment in Arid Regions. Darius J. Semmens Ph.D. Candidate, Watershed Management March 5, 2004. Acknowledgements. USDA-ARS Southwest Watershed Research Center David Goodrich, Scott Miller, Carl Unkrich

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentation

Geomorphic Modeling and Routing Improvements for GIS-Based Watershed Assessment in Arid Regions

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Geomorphic Modeling and Routing Improvements for GIS-Based Watershed Assessment in Arid Regions

Darius J. Semmens

Ph.D. Candidate, Watershed Management

March 5, 2004


Acknowledgements

  • USDA-ARS Southwest Watershed Research Center

    • David Goodrich, Scott Miller, Carl Unkrich

  • USGS – Waite Osterkamp

  • U of AZ

    • Phil Guertin, Richard Hawkins, Vicente Lopes, Craig Wissler

  • U.S. EPA, Landscape Ecology Branch

    • Bill Kepner, Bruce Jones

  • Betsy Semmens


Introduction

  • Hydrologic and geomorphic systems are defined and linked by the movement of water on the Earth’s surface

  • Management and planning for land and water resources is facilitated by watershed models

  • Recent improvements to watershed models have been primarily focused on humid environments

  • Arid regions characterized by processes operating at different temporal and spatial scales, thus require specialized conceptual models

  • This research addresses two limitations of arid-region distributed watershed models that hinder their use as assessment and planning tools

    • Limitation of spatial scale (hydrologic model)

    • Inability to simulate geomorphic response to landscape change (geomorphic model)


Problem Statement – Hydrologic Model

  • Small-watershed models designed to simulate short-duration ephemeral flows

  • Performance declines when applied to areas larger than about 100 km2

  • Large-watershed models simulate longer-term water balance

  • Performance declines when applied to areas smaller than about 1,000 km2

  • Ephemeral runoff in medium-sized arid-region watersheds is best described by small-watershed models

  • Modifications are needed to improve the performance of small-watershed models at larger scales


Problem Statement – Geomorphic Model

  • To understand how an individual stream reach responds to external stresses it is necessary to study the channel network as a whole

  • Geomorphic watershed models are thus necessary to evaluate long-term (years) impacts of landscape change

  • Event-based watershed models simulate erosion and deposition based on assumption that channel geometry is static during the course of an event

    • Prevents simulation of cumulative impacts from multiple events

  • No event-based watershed models that track cumulative adjustment of the channel network in terms of channel width, depth, and slope.


Identifying the Scale Gap in Watershed Modeling

Range of characteristic space – time scales

BMP

implementation

Ecosystem

restoration

Urbanization

Large WS Models (e.g. SWAT)

Small WS Models (e.g. KINEROS2)

Intermediate-Scale WS Models (This Research)

From: Bloschl and Sivapalan (1995)


Study Area

  • USDA-ARS Walnut Gulch Experimental Watershed

  • Semi-arid rangeland

  • Desert scrub (brush) and grassland

  • ~150 km2

  • Rainfall and runoff measured by a network of recording rain gauges, flumes, and weirs


Watershed

1 (WG1)

2

3

4

5

6 (WG6)

7

8

9

10

11 (WG11)

15

Area (km2)

148

112

9.42

2.29

22.1

93.6

13.6

14.8

23.9

15.8

7.85

23.7

nested subwatersheds and measuring devices

LH104 (0.047 km2)

Primary Watershed Areas


Hydrologic Model

  • Hypothesis

    • A significant source of error at intermediate scales results from the inability to account directly for diffusion of the flood wave as it is routed through the channel network

  • Approach

    • Implement Variable Parameter Muskingum-Cunge (VPMC) routing in KINEROS2 (Smith et al., 1995)

    • Compare with kinematic routing at multiple scales


Geomorphic Model

  • Hypothesis

    • A continuous-simulation, event-based geomorphic model describing channel width, depth and slope adjustments can predict reasonable geomorphic change in semi-arid watersheds

  • Approach

    • Implement channel-geometry adjustments in KINEROS2 based on total stream power minimization

    • Develop a GIS-based interface to facilitate model parameterization, multiple-event simulations, and results visualization

    • Evaluate generalized model behavior in absence of observed channel-geometry change

      • Sensitivity to initial channel geometry

      • Response to different precipitation records

      • Response to land-cover change


KINEROS2 Geomorphic Model (K2G)

  • Width and depth adjusted to minimize total stream power at end of each time step

  • Depth adjustments

  • Maximum erodible depth

  • Bank failure

  • Width adjustments

  • Compound channels

Depth


AGWA-G

  • GIS-based interface for K2G, customized version of AGWA

  • Watershed delineation and discretization

  • Land cover and soils parameterization

  • Coordinates multiple consecutive simulations and tracks cumulative outputs

  • Results visualization

  • Differencing results from two simulations – relative assessment


Geomorphic Model Testing

  • Observed, distributed precipitation input

  • SSURGO Soils

  • Hydraulic-geometry and observed-geometry channels

  • Four land-cover scenarios

  • Compare results for 1964, 1977, & 1978 monsoon season on WG11

Discretization

Elevation

Soils

Rain Gauges

1973

1997

All urban

Part urban


Simulation Inputs

Sediment grain-size distributions

Land-cover scenarios

Precipitation record characteristics for the 1964, 1977 and 1978 monsoon seasons


Results

1964

  • Hydraulic-geometry channels

  • 1997 land cover

  • Wet (top), intermediate (middle), and dry (bottom) year simulation results

  • Depth changes mapped on the left, width changes mapped on the right

  • Erosion during wet year, and deposition during dry year

Decreasing Precipitation

1977

1978


Results

1964

  • Hydraulic-geometry channels

  • Partially urbanized land cover

  • Differences from 1997 land cover not obvious

  • Less erosion within, and more deposition and downstream of urbanized tributary

Decreasing Precipitation

1977

1978


Results

1964

  • Runoff depth (mm) per unit contributing area

  • Runoff highest as flows coalesce in the headwaters, then decreases in the downstream direction because of channel infiltration

  • Significant decreases occur further upstream for drier years

  • Deposition occurs downstream of transition

Decreasing Precipitation

1977

1978


Results

1964

  • Observed-geometry channels

  • 1997 land cover

  • Wet (top), intermediate (middle), and dry (bottom) year simulation results

  • Depth changes mapped on the left, width changes mapped on the right

  • Reach adjustments more spatially varied with observed channels

Decreasing Precipitation

1977

1978


Results

1964

  • Observed-geometry channels

  • Partially urbanized land cover

  • Reach adjustments more spatially varied with observed channels

  • Can see preferential change on southern tributary

Decreasing Precipitation

1977

1978


Mass-Balance Error

  • Mass-balance error for modeled change in sediment storage (red) and equivalent mass of geometric adjustment (blue) for entire channel network

  • Modeled cumulative magnitude of deposition/erosion (burgundy), and equivalent mass of geometric adjustment (cream)

  • Geometric adjustments conserve mass reasonably well for hydraulic-geometry simulations, but not for the observed-geometry simulations

Mass-balance error (%)

Magnitude of deposition/erosion (kg)


Relative Assessment

  • Error in watershed modeling is substantial

  • Even carefully calibrated models yield poor results when applied to events significantly larger or smaller than those used in the calibration

  • Geomorphic model is thus most useful for evaluating where in the watershed change is likely to be most significant

  • Assuming the basic processes are represented accurately, and error is spatially uniform, it can be largely removed through differencing simulation results

  • Relative assessment can thus identify general patterns of response to landscape change, even if the specific magnitude of that change is not correct


Results – Relative Assessment

  • Hydraulic-geometry channels

  • Difference in computed depth (left) and width (right) changes between PU and 97 simulation results for wet (top) and intermediate monsoon seasons

  • Significant differences concentrated on urbanized tributary

  • Erosion increases within urbanized area more pronounced for wet year

  • Reduced erosion or increased deposition begins further upstream during drier year

  • Aggradation downstream characterized by depth decreases and width increases

1964

Decreasing Precipitation

1977

Difference in depth changes

Difference in width changes


Results – Relative Assessment

  • Observed-geometry channels

  • Magnitude of differences is different from the hydraulic geometry simulations

  • Pattern of adjustment very similar to that for the hydraulic-geometry channels – erosion in urbanized area and deposition downstream

  • Suggests that channel slope and discharge are the most important parameters governing channel response

1964

Decreasing Precipitation

1977

Difference in depth changes

Difference in width changes


Hydraulic-Geometry Channels

Observed-Geometry Channels

Results

  • Wet monsoon cumulative runoff (mm), infiltration (m3/km), and sediment yield (kg/ha)

  • Runoff increases from urbanization decrease in downstream direction

  • Infiltration increases in downstream direction

  • Sediment yield increases from urbanization increase in downstream direction

  • Spatial patterns very similar for both hydraulic and observed geometries

  • Increased deposition downstream where stream power decreases

Runoff

Runoff

Infiltration

Infiltration

Sed. Yield

Sed. Yield


Hydraulic-Geometry Channels

Observed-Geometry Channels

Results

  • Intermediate monsoon cumulative runoff (mm), infiltration (m3/km), and sediment yield (kg/ha)

  • Runoff increase from urbanization dissipates more rapidly in downstream direction

  • Infiltration increase peaks further upstream

  • Sediment yield increase peaks further upstream

  • Locus of deposition shifts upstream

  • Spatial patterns very similar for both hydraulic and observed geometries

Runoff

Runoff

Infiltration

Infiltration

Sed. Yield

Sed. Yield


Conclusions – Geomorphic Model

Individual Batch Simulations

  • Network-wide mass conservation is reasonable when hydraulic-geometry channels are used, but needs work for more variable observed-geometry channels

  • Erosion is most widespread during the wettest year, erosion and deposition mixed during intermediate year, and most widespread deposition for driest year

  • Specific channel adjustments sensitive to initial channel geometry – more uniform for hydraulic-geometry channels


Conclusions – Geomorphic Model

Relative Assessment

  • Results of the scenario-output differencing show the concentration of impacts within and downstream of the urbanized area, and no significant changes in the unaffected areas

  • Geomorphic impacts of urbanization varied with the number and magnitude of precipitation events, but the general response was erosion in the urbanized area and deposition downstream

  • Spatial pattern of geomorphic response closely linked to changes in cumulative runoff and channel infiltration

  • Spatial pattern of geomorphic response relatively insensitive to initial channel geometry, suggesting that a suitable hydraulic-geometry relation may be sufficient for broad-scale application of the model


Future Research – Geomorphic Model

  • Model validation – need to demonstrate that simulated geomorphic adjustments are representative of observed adjustments

  • Increase upper watershed size limit for K2G

    • Diffusion-wave routing

    • Discritization of channel

  • Link simulated geomorphic change and channel stability, or vulnerability to degradation

    • Evaluate model behavior over broader range of precipitation records, and over longer periods of time

    • Evaluate model response to major disturbance, and whether response is persistent or transitive

  • Link simulated geomorphic change and riparian condition


ad
  • Login