Austin Creek Stream FlowOctober 2001 through December 2001

0

100

200

300

400

500

600

700

10/01/2001-00:00:00

10/11/2001-00:00:00

10/21/2001-00:00:00

10/31/2001-00:00:00

11/10/2001-00:00:00

11/20/2001-00:00:00

11/30/2001-00:00:00

12/10/2001-00:00:00

12/20/2001-00:00:00

12/30/2001-00:00:00

Date and Time

Dis

ch

arg

e (

cfs

)

Recorded

Simulated

Smith Creek StreamflowOctober 2001 to December 2001

0

50

100

150

200

250

300

350

10/01/2001-00:00:00

10/11/2001-00:00:00

10/21/2001-00:00:00

10/31/2001-00:00:00

11/10/2001-00:00:00

11/20/2001-00:00:00

11/30/2001-00:00:00

12/10/2001-00:00:00

12/20/2001-00:00:00

12/30/2001-00:00:00

Date and Time

Dis

ch

arg

e (

cfs

)

Recorded

Simulated

Calibration of Distributed Hydrology-Soils-Vegetation Model to Lake Whatcom Watershed, Washington State

Katherine Callahan and Robert Mitchell, Western Washington University, 516 High St. Bellingham, WA 98225Pascal Storck, 3 Tier Environmental Forecast Group, 2825 Eastlake Ave. East, Seattle, WA 98102

Lake Whatcom watershed is located in the North Cascades foothills in northwestern Washington (Figure 1). The watershed was chosen for this study because the lake provides the drinking water supply for approximately 86,000 people and water managers are concerned about sustaining the lake as a long term drinking water source. The watershed characteristics are described below.

DHSVM is a physically based, spatially distributed hydrology model that simulates watershed hydrology through a multilayer grid system at the pixel level. Each pixel in the grid is assigned various characteristics such as soil type, vegetation type, elevation, slope, depth to water table (Figure 2). This model was developed at the University of Washington specifically for watersheds in the Puget Sound and Cascade Mountains (Wigmosta et al., 1994).

References:

Miller, D.A. and R.A. White, 1998: A Conterminous United States Multi-Layer Soil Characteristics Data Set for Regional Climate and Hydrology Modeling. Earth Interactions, 2. [Available on-line at http://EarthInteractions.org]

Storck, P., L. Bowling, P. Wetherbee, and D. Lettenmair, 1998. Application of a GIS-based distributive hydrology model for prediction of forest harvest effects on peak stream flow in the Pacific Northwest. Hydrological Processes vol. 12, pp 889- 904.

Vogelmann, J.E., S.M. Howard, L. Yang, C.R. Larson, B.K. Wylie, N. Van Driel, 2001. Completion of the 1990s National Land Cover Data Set for the Conterminous United States from Landsat Thematic Mapper Data and Ancillary Data Sources, Photogrammetric Engineering and Remote Sensing, 67:650-652.

Wigmosta, M., L. Vail, and D. Lettenmair, 1994. A distributed hydrology-vegetation model for complex terrain. Water Resources Research, vol. 30 no. 6, pp 1665-1679.

Acknowledgements:I would like to thank my thesis committee members: Dr. Robert Mitchell, Dr. Doug Clark, Dr. David Wallin, and Mr. Steve Walker. In addition, I would to thank WWU and the Institute for Watershed Studies for their assistance in funding this research and Jay Chennault for his continued assistance with modeling and GIS.

INTRODUCTION

Lake Whatcom Watershed

METHODS

Calibration means modifying the basin attributes and/or meteorological data to satisfactorily match the discharge predicted by the model to the actual discharge recorded at the gauge. The model is being calibrated to a time series of river-discharge data collected from the Smith Creek and Austin Creek (Figure 1).

PRELIMINARY RESULTS

Austin Creek Stream FlowJanuary 2002 through March 2002

0

50

100

150

200

250

300

350

400

450

500

01/01/2002-00:00:00

01/11/2002-00:00:00

01/21/2002-00:00:00

01/31/2002-00:00:00

02/10/2002-00:00:00

02/20/2002-00:00:00

03/02/2002-00:00:00

03/12/2002-00:00:00

03/22/2002-00:00:00

Date and Time

Dis

ch

arg

e (c

fs)

Recorded

Simulated

Smith Creek Stream FlowJanuary 2002 to March 2002

0

50

100

150

200

250

10/01/2001-00:00:00

10/11/2001-00:00:00

10/21/2001-00:00:00

10/31/2001-00:00:00

11/10/2001-00:00:00

11/20/2001-00:00:00

11/30/2001-00:00:00

12/10/2001-00:00:00

12/20/2001-00:00:00

Date and Time

Dis

ch

arg

e (

cfs

)

Recorded

Simulated

Differences between the actual gauge location along the creeks and the location where the model is predicting discharge.

Inadequate soil data. The soil thickness and permeability will influence the magnitudes of the peaks. We have not altered predicted soil thickness values in the basins or sufficiently quantified values for the bedrock in the watershed (fractured sandstone).

Unsatisfactory precipitation lapse rate predictions. Point precipitation is distributed through the watershed via algorithms in DHSVM. We have not fully explored all lapse rate variability options.

Inaccurate solar radiation inputs may be influencing transpiration and soil storage. We have not performed simulations using the aspect grid which models shortwave radiation based on topographic aspect and slope variability.

Distributed Hydrology-Soils-Vegetation (DHSVM) Model

Watershed area ~146 km2

Lake area ~21 km2

Elevation ranges from 93 meters at the lake to 1024 meters at the highest point

Urban area covers ~9 km2

Forested areas cover ~117 km2

Nine stream gauges are located in the watershed

Two climate stations exist within the watershed

DHSVM performs an energy and water mass balance on each pixel. Then all the pixels are linked through a subsurface transport method: Darcy’s Law determines downward movement and flow is exchanged between pixels based on topography (Figure 3) (Storck, et al., 1994).

Northshore Climate Gage

0

0.01

0.02

0.03

0.04

0.05

0.06

10/1/2001 10/31/2001 11/30/2001 12/30/2001 1/29/2002 2/28/2002 3/30/2002

Date

Pre

cip

itat

ion

(m

ete

rs)

-6

-4

-2

0

2

4

6

8

10

12

14

16

Tem

per

atu

re (

Ce

lsiu

s)

Precipitation

Temperature

Climate data were taken from the Northshore station (Figure 1). DHSVM requires the following climate data:

DHSVM requires multiple input grids to characterize the watershed.

30 meter DEM provides a 30m pixel size for model calculations (Figure 1)

Stream Network (generated by Arc/Info AML) (Figure 1)

CONUS soil types (Miller and White, 1998) (Figure 5)

USGS National Land Cover Data Set (Figure 6)

Soil Depth (generated by Arc/Info AML) (Figure 7)

Figure 1. DEM of Lake Whatcom Watershed with Stream Network, and Two Primary Subbasins

Figure 2. DHSVM Model Representation of the 1-D Vertical Water Balance

Figure 3. DHSVM Surface and Subsurface Flow Routing and Runoff Generation

Figure 4. Daily Precipitation and Temperature DataFrom the Northshore Climate Station near Smith CreekSubbasin

Figure 5. CONUS Soil Types

Figure 6. Land Cover Data from USGS Figure 7. Soil Depths generated by AML Script

Figure 9. Comparison of Smith Creek Simulated Discharge to Recorded Flow

Figure 8. Comparison of Austin Creek Simulated Discharge to Recorded Flow

Research Objective

Our goal is to quantify the surface water runoff from the watershed into the lake under varying climatic conditions using the Distributed Hydrology-Soils-Vegetation Model (DHSVM). The watershed is suitable for modeling purposes because it contains

Input Grids

Meteorologic Inputs

Model Simulation

Although we are in initial phase of model calibration, we are satisfied with the preliminary results. The model is capturing the timing of peaks reasonably well, but it is over estimating the volumes. The simulated flow over estimates the gauge volume by approximately 25% for Austin Creek (Figure 8) and by about 64% for Smith Creek (Figure 9). We believe the over estimates are attributed to one or more of the following:

Comparison of Predicted and Recorded Discharge

FUTURE WORK

Our preliminary calibration results are encouraging. We are confident that we will accurately calibrate DHSVM by refining the basin characteristics and meteorological inputs. Once calibrated the model will be used to explore surface runoff scenarios in the watershed such as the influence of logging and increased urban development. We are also interested in quantifying groundwater inputs into the lake using DHSVM.

Data logging stream gauges on three perennial streams

Two weather stations that collect solar radiation, temperature, humidity, and precipitation data

Gauges that log hourly lake levels and hydraulic inputs and outputs for the lake

Precipitation (m)

Wind Speed (m/s)

Relative Humidity (%)

Longwave Radiation (estimated from station data) (W/m2)

Shortwave Radiation (W/m2)

Temperature (oC)

Climate data covers a period from January 1, 2001 and ends July 31, 2003

Initial model state of the watershed was determined using the entire climate input-time series

Initial calibration simulation covered the time frame from October 1, 2001 to March 31, 2002

Stream segments that terminate near the stream gauges were selected for output during model simulations

It takes approximately 24 hours for DHSVM to perform one calibration simulation on a SUN E450

130-5 Abst. No. 66494