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Henry Hagg Lake Water Quality Model -- Scenarios

Background | Objectives & Approach | Significant Findings
Selected Results | Model | W2 Modifications | Downloads | Project Home

Background

Henry Hagg Lake near Sain Creek (Photo by S. Rounds, 22-Sep-2004)

More information on Henry Hagg Lake, Scoggins Dam, and the USGS water-quality model of the lake is available at the Henry Hagg Lake water quality model website. In short, Henry Hagg Lake is a constructed reservoir in the Tualatin River Basin in northwestern Oregon. It is used for flood control, recreation, and as a source of municipal, industrial, agricultural, and flow-augmentation water. Local water managers, in planning to meet the needs of a growing population, have several options for new sources of water. One option is to expand Hagg Lake by increasing the height of Scoggins Dam. This work was performed in an effort to better understand how the temperature and water quality in the lake, and downstream, might change if Scoggins Dam were to be raised by as much as 40 feet. The "new" water would be used primarily as municipal drinking water and as flow-augmentation water for the Tualatin River.

Objectives & Approach

Once the USGS water-quality model of Hagg Lake was constructed and calibrated, it was used to predict the changes in circulation, temperature, and quality that might result from a suite of potential dam modifications. Thirty-six model scenarios were run, using various combinations of dam raises, outlet configurations, methods for supplementing lake inflows, and downstream release schedules. Most of the model scenarios were run using the hydrologic and meteorologic conditions from 2002, which was a typical year. Several of the scenarios also were run while imposing conditions from 2001, a drought year. Model scenarios were run for an entire calendar year so that seasonal temperature and water-quality variations and the efficacy of inflow and release schedules could be examined over their entire range.

Dam Raise

The scenarios evaluated the effects of three different height increases to Scoggins Dam: 20, 25, and 40 feet. These levels of raising the dam resulted in a total simulated lake storage of 88,800, 95,800, and 118,000 acre-feet, respectively. Simulated storage in the existing lake is 63,900 acre-feet.
 

Water Deliveries

Two different levels of water releases were simulated in these scenarios. The "a" scenarios used a low level of water releases from the lake, in keeping with how water might be used just after a dam raise. Under those conditions, little of the new municipal water would be required, but all of the water designated for downstream flow augmentation would be released according to a prescribed schedule. Under "b" scenarios, a higher level of release was imposed that represented a future time when all of the new municipal water was needed.
 

Inflow Augmentation Method

Depending on the level of the dam raise, a method to provide additional inflows to the lake might be needed in order to assure that the expanded reservoir fills during in the winter season. Three different options were simulated: no enhanced inflow, diversion of water from the upper Tualatin River through a tunnel that ended in the Sain Creek arm of the lake, and pump-back of water from the Tualatin River near Forest Grove uphill through a proposed pipeline to the dam.
 

Outlet Configuration

Several combinations of outlets were tested with the model: no change (just the original lake outlet), addition of a second fixed-elevation outlet near the lake's current full-pool level, addition of a variable-elevation outlet, or removal of the original outlet and addition of a variable-elevation outlet. If more than one outlet was used, or if a variable-elevation outlet was used, the flows from the outlets and the depth of the variable-elevation outlet were adjusted in an attempt to meet a hypothetical downstream temperature time series in Scoggins Creek downstream of the dam.

The details of each of the scenarios and the results of this investigation are documented in USGS Scientific Investigations Report 2006-5060:

Sullivan, A.B. and Rounds, S.A., 2006, Modeling water-quality effects of structural and operational changes to Scoggins Dam and Henry Hagg Lake, Oregon: U.S. Geological Survey Scientific Investigations Report 2006-5060, 36 p.
[Available online at http://pubs.usgs.gov/sir/2006/5060/]

Significant Findings

1. The proposed dam raise and associated changes to the lake's inflows and releases are likely to produce important and measurable changes in water quality, both in the lake and in the water released downstream to Scoggins Creek.
    
2. Compared to the base case (observed conditions), most modifications considered in these scenarios led to cooler annual average water temperatures, less anoxia and lower annual average concentrations of ammonia and chlorophyll a.
    
3. The amount of water withdrawn from Hagg Lake has water quality implications. Model scenarios with low water levels produced warmer lake temperatures, earlier turnover and higher ammonia concentrations in the hypolimnion compared to scenarios with higher water levels. In the outflow, low lake levels led to more frequent exceedence of downstream temperature standards.
    
4. Diversion of water into Hagg Lake from the upper Tualatin River and pump-back from the Tualatin River downstream would fill an enlarged lake (25- or 40-ft dam raise) in 2002. In a drought year such as 2001, however, pump-back would not necessarily fill the enlarged lake, as water levels were low at the start of the year and drought reduced the availability of pump-back water in the Tualatin River downstream.
    
5. Simulations of the wintertime transfer of water into Hagg Lake from the Tualatin River via the pump-back option resulted in increased phosphorus concentrations in the lake, especially in 2002 due in part to high concentrations of orthophosphate in the pump-back water that year.
    
6. Water temperature standards in Scoggins Creek downstream of Scoggins Dam will likely not be met without the construction of additional lake outlets to allow the blending of warm and cold water from various depths in the lake.
    
7. Model predictions indicate that blending water from near the lake's surface (typically warm in the summer) with water from near the lake bottom (typically cold) is sufficient to meet downstream temperature standards and restore a more natural seasonal temperature pattern in Scoggins Creek below the dam. A selective withdrawal tower with sliding gates or multiple fixed outlets would offer dam operators the necessary flexibility for blending.
    
8. The use of multiple lake outlets and various operational strategies has important effects on water quality in the lake. Hypolimnetic anoxia and the subsequent buildup of hypolimnetic ammonia can be minimized or avoided. Lake surface temperature maxima can be decreased, which may help to minimize blooms of the blue-green algae anabaena planctonica.

Selected Results

One of the more useful and interesting ways to visualize model output is by viewing a time-indexed color plot of vertical profiles. In this type of plot, a vertical profile of temperature or the concentration of some simulated substance is shown as a function of time and elevation, with the temperature or substance concentration represented by a color. The plot below is an example of such a visualization for temperature for the 2002 calibrated conditions.

Time in these plots is always on the X axis, with January 1st on the left and December 31st on the right. Elevation is on the Y axis. Note how this plot includes how the water-surface elevation of the lake changes over the course of the year -- highest in May and lowest in October or November due to summertime releases for downstream users. The heavy black line running across the figure indicates the level of the lake's outlet; some plots will have more than one line because some scenarios used more than one lake outlet. Finally, the temperature at each elevation and date is plotted according to the color scale shown at the bottom of the plot; in this case, deep blue is cold water and dark red is warm water. This information is valid only for a specific location in the lake -- all of these vertical profiles are taken from the deepest part of the lake near the dam. Fortunately, water-quality variations in the lake are strongest along the vertical dimension, so this representation, though taken from the deepest part of the lake near the dam, is fairly valid as a representation of conditions in most of the lake.

Thirty six model scenarios were run, and these time-indexed color plots of vertical profiles are available here for each model run for temperature, dissolved oxygen, ammonia, and chlorophyll. You may download the entire set of plots [ZIP, 2.44 Mb], or view the individual PNG images through the links in the table below. For the details of each model scenario, see the report.

Model

The model source code and the compiled executable used in these scenarios is available for download [ZIP, 779 Kb]. The model was compiled to run on the Windows operating system, but can be compiled and run on any system that has a FORTRAN 95 compiler. Although CE-QUAL-W2 is available with a graphical user interface, the copy distributed here is a generic version that does not include the interface. The generic version produces the same results, but simply provides less feedback to the model user during the run. The generic version of the model was used exclusively by USGS personnel in this investigation.

The USGS model was a modification of version 3.12 (dated 15-Aug-2003) of the CE-QUAL-W2 source code. Modifications included the addition of a zooplankton group, a new subroutine for the blending of withdrawals to meet downstream temperature targets, and several updates to correct coding bugs, as documented on the CE-QUAL-W2 website. The model was compiled using the Compaq Visual Fortran compiler (version 6.6.A) with the following options:

  /fast /nodebug /real_size:64
  /warn:(argument_checking,nofileopt,unused,nousage)

For these model scenarios, the USGS modeling team added a new subroutine to CE-QUAL-W2 to allow the model to blend water from multiple outlets, and adjust the elevation of a variable-elevation outlet, in an attempt to meet a user-specified downstream temperature target. This new subroutine was not present (and was not needed) in the model code used in the first phase of this study, in which the model of Hagg Lake was constructed and calibrated. The new subroutine is documented in the model scenario report cited above and also in the following paper:

Rounds, S.A. and Sullivan, A.B., 2006, Development and use of new routines in CE-QUAL-W2 to blend water from multiple reservoir outlets to meet downstream temperature targets, in Proceedings of the Third Federal Interagency Hydrologic Modeling Conference, April 2-6, 2006, Reno, NV: Subcommittee on Hydrology of the Interagency Advisory Committee on Water Information, ISBN 0-9779007-0-3.
(full text [PDF, 198 Kbytes])

Downloads

Download reports:

- Henry Hagg Lake model construction & calibration
- Henry Hagg Lake model scenarios
- Modifications to CE-QUAL-W2 [PDF, 198 Kb]
 

Download model results:

- Time-indexed vertical profile plots [ZIP, 2.44 Mb]
 

Download the model used for the Hagg Lake scenarios:

- Source code, compiled program, and notes [ZIP, 779 Kb]
 

Download GIS coverages:

- Scoggins Creek drainage & Hagg Lake bathymetry

Questions? Comments? For more information about this project, contact:

Stewart Rounds
U.S. Geological Survey
2130 SW 5th Avenue
Portland, OR 97201
503-251-3280
sarounds@usgs.gov

Oregon Water Science Center Home page
Oregon Water Science Center Hydrologic Studies page
Tualatin Water Quality Assessment page
Henry Hagg Lake Water Quality Model page