SPDSS_Task2_IDKeyStreamflowGages

• Title: SPDSS Task 2 - Identify Key Streamflow Gages and Estimate Streamflows for Missing Records
• Description: The objective of this task is to identify key streamflow gages to use in the SPDSS modeling efforts and to develop a method for filling missing data. Revised memo to account for new information regarding the Balzac Gage. Revised February 2007.
• Decision Support - Doc Type: Task Memorandum
• Date: 2/10/2007
• DSS Category: Surface Water
• DSS: South Platte
• Basin: South Platte
• Contract/PO #: C153954
• Grant Type: Non-Reimbursable
• Bill Number: SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
• Prepared By: Leonard Rice Engineering

The SPDSS Feasibility Study (FS) provided an inventory of over 300 stream gages located in the
South Platte, North Platte, and Laramie River basins (SPDSS study area). The FS found that
approximately 45 streamflow gages had less than 10 percent missing records and 65 streamflow
gages had less than 30 percent missing records for the period of 1950 through 2000. The FS
determined that the spatial coverage of these gages is adequate for development of surface water,
ground water, and water budget models.
Where to find more information
^ The South Platte Decision Support System Feasibility Study Final Report, October 2001
is available on the State's website (http://cdss.state.co.us).
Based on the SPDSS FS data assessment, "key streamflow gage" will be defined as follows for
potential future SPDSS surface water, ground water, and water budget modeling purposes:
Key Streamflow Gage -Streamflow gage located within the SPDSS study area with:
• Good or excellent records based on USGS ratings,
• At least 70 percent of the records complete throughout the SPDSS study period
(1950 through the current year available; 1950-2002 at this time), or
• The best available data at an important location.
This task is in support of potential future modeling which will be referred to throughout this
memo as modeling, for simplicity. The objective of this task is to:
1. Identify key streamflow gages for the SPDSS surface water, ground water, and water
budget modeling. A unique set of gages may be identified for each model (a gage maybe
considered key for only one model and not the other two models).
2. Fill missing records for the key streamflow gages to be used in the ground water and the
water budget modeling (gages for the surface water model do not need to be filled).
Approach and Results -Identify Key Streamflow Gages for the SPDSS Surface Water,
Ground Water, and Water Budget Modeling
The analyses for this task were based on monthly data extracted from the State's database,
HydroBase. If HydroBase contains a monthly streamflow value, then it also contains daily data
for every day within that month. If a monthly value is missing, HydroBase may still contain
daily data for many days within the month; just one missing daily value will trigger a missing
monthly value. A brief review of daily streamflow gage data showed that there are not typically
sporadic missing daily values and that a missing monthly value is typically associated with most
or all of the days within that month missing.
The first step in identifying key streamflow gages for the SPDSS surface water, ground water,
and water budget modeling was to extract monthly gage records from HydroBase using the
TSTooI Data Management Interface (DMI). Most of the historical records in HydroBase are
from USGS streamflow gages. The State of Colorado has also installed streamflow gages in
more recent years and has taken responsibility for many USGS gages that would have otherwise
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