Third Creek STREAMDO Model

Overview

STREAMDO was the model chosen to predict the DO levels in Third Creek resulting 

from oxygen demanding loads. STREAMDO is a model that is capable of modeling a 

wide range of processes that affect water quality. In addition, STREAMDO has been 

used to model Segment 15 of the Platte River and used widely throughout the U.S. 

Environmental Protection Agency (EPA) Region VIII.

The basis for model construction is data collected as part of the loading based sampling 

events. The remainder of this appendix discusses model construction, calibration, and 

validation.

Model Construction

STREAMDO is a spreadsheet model employed to determine steady state DO 

concentrations as well as ammonia toxicity. The format is very convenient for modifying 

model structure and inserting additional processes. The following are key construction 

components of the model:

 Streamflow

 Stream velocity

 Stream temperature

 Observed instream DO concentrations

 Minimum and maximum daily DO concentrations

 CBOD

 Organic nitrogen

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 Total ammonia

 Un-ionized ammonia

 Nitrate and nitrite

 pH

 Sediment Oxygen Demand (SOD)

 Stream depth

 Chlorophyll-a

STREAMDO calculates water quality conditions in specified computational elements or 

"segments" throughout the water body of interest. The model requires that data be 

entered for each segment entering the water body and upstream conditions. Observed 

water quality parameter values are entered for the conditions at the end of each model 

segment for output comparison. The model is constructed to simulate the mainstem of 

Third Creek starting from below the C+ pond, WQTC01, to where Third Creek meets 

Tower Road, WQTC06. This section of the creek that the model focuses upon is 

approximately 4 miles in length. The mainstem of Third Creek has been separated into 

four uniform segments, each representing a 1-mile reach as shown in the following 

figure.
Model Calibration and Validation

The results of receiving water simulations are more meaningful when some sort of 

confirmatory analysis accompanies them. Calibration involves minimization of 

deviation between measured field conditions and model output by adjusting parameters 

of the model. Data required for this step are a set of known input values along with 

corresponding field observation results. The results of the calibration effort provide 

information as to which parameters have the greatest effect on output. Validation 

involves the use of a second set of independent information to check the model 

calibration.

During Loading Events 1 and 2, data was collected on two occasions; April 12, 2001 

(Event 1) and April 23, 2001 (Event 2). The second sampling event was chosen for model 

calibration because of its typical characteristics; flow, loading, and deicing operations at 

the airport. During the first sampling event, the airport was shut down for a period 

creating atypical loading conditions in the creek.

Due to the variation in events at DIA, it was appropriate to also calibrate to a mid-winter 

cold event where runoff volume is relatively small compared to typical fall and spring 

storms that generate more runoff. After comparing data collected during LB3 with LB4 it 

was determined that data from LB4 should be used for calibration purposes although 

results from an attempt to calibrate to LB3 conditions are also contained within this 

appendix. Both events occurred during low flow and freezing conditions.

The major calibration target is DO concentrations in Third Creek. For LB4, the travel 

time in Third Creek during the events was used to assess which DO concentrations to 

set as calibration targets in the model. The travel time of Third Creek was estimated at 

3.9 miles per day based on an average measured stream velocity of 0.24 feet/second 

during the fourth event. The actual travel time is most likely less than the estimated 

value due to freezing on Third Creek during portions of the day during the sampling 

period. Based on the estimated travel time, it is anticipated that the de-icing load from 

the precipitation event should have passed by WQTC04 by January 26, 2002. Therefore, 

instantaneous DO concentrations measured in the field during LB4 were utilized for 

calibration purposes. 

Input Parameters

The parameters inputted to STREAMDO prior to calibration of model coefficients are: 

flow, velocity, depth, temperature, DO, DeltaDO, CBOD5

Upstream #1 WQTC02 #2 WQTC03 #3 WQTC04 #4 WQTC06

Mile: 0 1 2 3 4

WQTC01 WQTC05

, organic nitrogen, ammonia, 

Model Segmentation
un-ionized ammonia, nitrate-nitrite, pH, and chlorophyll-a. These values were measured 

or calculated based on data collected in the field.

Loading Based Events One and Two

The April 23, 2001 loading event (LB2) sampling data was chosen for model calibration 

for spring conditions. Two flow values were used in model input. One was an initial 

flow of 14.68 cfs plus tributary flow. Tributary flow was calculated using two methods. 

The first method was to use the measured tributary flow 0.07 cfs at WQTC05. The 

second method was part of the calibration procedure where the difference in observed 

mainstem flow was considered to be the tributary flow contribution. During LB2, the 

mainstem flow rates at WQTC01 and WQTC02 were 14.68 and 16.63 cfs respectively. 

Thus, the tributary flow, the difference in mainstem flows, was calculated to be 1.95 cfs. 

The velocities used in the model were based upon data collected during loading 

sampling LB2. These were the actual velocities observed in the creek. This assumption 

can be contrasted by using the flow contributions in the mainstem from the upstream 

reach and tributary to back calculate the velocity in each reach, thus keeping continuity 

in the mainstem. The velocity in the mainstem was calculated as the average velocity 

from the sampling event data at each location. This computation takes the crosssectional area and divides it by total flow. The average depth in the channel was 

calculated at each location using the cross-sectional data collected during the sampling 

event. The mean depth is calculated by the cross-sectional area divided by the width.

The temperature, DO, and pH data was obtained from the field measurements taken at 

the sampling event by an instream monitoring device. This data can be found in the 

Section 3 of this report.

The model parameter DeltaDO is the difference between the daily maximum DO 

concentration and the minimum DO concentration. The DeltaDO is used to estimate the 

amount of DO used in daily photosynthesis activities and used to estimate the total DO 

deficit in the stream. This amount is estimated from data collected by two in situ DO 

sampling devices located in the creek. During this second sampling event, the DeltaDO 

is estimated to be 1.25 mg/L.

CBOD5

The SOD was estimated from literature values. Typical SOD values for sandy bottom 

streams ranged from 0.2 to 1.0 g/m

data were obtained from LB2 sampling results (see Section 3). The 

concentrations for ammonia, un-ionized ammonia, nitrate-nitrite, and chlorophyll-a

were also obtained from LB2 sampling results. 

2/d. In the temperature range 0 to 5°C, SOD rates 

approach zero (Chapra 1997). Due to winter, conditions and temperatures observed 

during the loading sampling event an SOD value of 0.1 g/m2/d was used as a model 

input.
Loading Based Events Three and Four

During both the third and fourth events, some of the sites on Third Creek were iced 

over, which made flow measurement difficult. Flow was determined by sites, which 

were mostly free of ice or where ice was easily broken making flow measurement 

possible. The following sites were used to determine average flow in Third Creek during 

LB3: WQTC01, WQTC02, WQTC05, WQTC06. A total flow of 0.4 cfs was used for 

modeling purposes and a tributary flow base of 0.04 cfs was assumed based on 

measurements at WQTC05. During the fourth event the following sites were used to 

determine average flow in Third Creek: WQTC01, WQTC02, and WQTC03. A total flow 

of 0.22 cfs was used for modeling purposes. Since flow was obstructed at WQTC05 due 

to construction, a tributary flow base of zero was assumed. Average velocities and 

depths were calculated using the stations designated for each event. Calculations for 

flow can be found at the end of this appendix.

Observed temperature, DO, CBOD5

Calibration Parameters

, organic nitrogen, ammonia, un-ionized ammonia, 

nitrate-nitrite, pH, and chlorophyll-a were based on observed data from field data 

collection. DeltaDO was calculated using the Sonde located downstream of WQTC01. 

The average of the daily DeltaDO for the period of data collection was used for 

calculation purposes. DeltaDO is used in STREAMDO for calculating the photosynthesis 

coefficient used in the model.

Rate coefficients representing reaeration, BOD, nitrification, and SOD are utilized by 

STREAMDO to predict instream DO levels. Following is a description of these 

parameters:

 K1 is the carbonaceous deoxygenation rate coefficient (l/day)

 K2 is the reaeration rate coefficient (l/day)

 K3 is the ammonia nitrification rate coefficient; reflects nitrogenous oxygen demand 

due to conversion of NH3 to (NO2 + NO3

 K4 is the ammonification rate coefficient; reflects the conversion of organic nitrogen to 

ammonia nitrogen (l/day)

) (l/day)

 K5 is the ammonia loss rate coefficient; reflects non-DO consuming activities, which 

result in a loss if ammonia such as ammonia volatilization and direct assimilation to 

aquatic life and bacteria (l/day)

 K6 is the nitrate/nitrite loss coefficient; reflects non-DO consuming activities, which 

result in loss of nitrate/nitrite including denitrification and direct assimilation to 

aquatic plants and bacteria (l/day)

 S Benthic demand coefficient; reflects the DO burden caused by the benthic 

utilization, otherwise known as SOD (g/m2/day)
The typical ranges for the STREAMDO parameters as stated in the QUAL2E Users 

Manual (EPA/600/3-87/007, 1987), EPA's Rates, Constants, and Kinetics Formulations in 

Surface Water Quality Modeling (EPA/600/3-85/040, 1985) and Chapra (1997) are shown 

in the following table.

Published Parameter Ranges

Coefficient Range

CBOD5 coeff K1 (1/day) 0.02 - 3.4

Reaeration coeff K2 (1/day) 0 - 100

NH3 coeff K3 (1/day) 0.1 - 2.0

Organic N coeff K4 (1/day) 0.02 - 0.4

NH3 Loss K5 (1/day) (a)

NO2 + NO3 K6 (1/day) 0 - 1.0

Benthic Demand S (g/m 2/day) 0.2 - 1.0

(a) No published ranges available, assumed low due to lower pH observed 

during data collection activities.

The calibration effort showed that K1 and K2 had the most effect on DO concentrations. 

K2 was inputted into the model prior to modifying K1 concentrations as K2 was 

calculated using the Owens and Gibbs formula:

where: U is the mean velocity in fps

H is the mean depth in feet

Due to LB2 conditions, the ammonia nitrification rate coefficient, K3, was determined to 

be at the lower end of published values due to winter conditions, indicating a slow 

conversion from ammonia to nitrate and nitrite. This slow reaction rate was also seen in 

the parameters for ammonification rate (K4), ammonia loss rate (K5), and benthic oxygen 

demand (S). The nitrate/nitrite loss rate (K6

The model was calibrated using Event 2 data in two ways. First, the model was 

calibrated with observed data assuming no additional loading or flows. Second, the 

model was calibrated again with observed data but with an additional CBOD

) was calibrated using published values as a 

guide, but there is a sudden loss in concentration in the observed values at stations TC04 

and TC06 indicating a higher than normal loss rate in the third and fourth segments. 

5 loading 

(flow and concentration) in the first segment forcing the CBOD5

The concentration of CBOD

conditions to reflect the 

concentrations observed in Third Creek at WQTC02. Currently, the model does not 

include any additional groundwater or lateral inflows due to additional drainage area 

other than the tributary (WQTC05) entering Segment 1.

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1.85

0.67

2 21.6

H

U k =

in the first segment of the model was calculated by the 

mixing of upstream conditions and the loading from the tributary draining the northern 

part of Runway 34/16, WQTC05. The concentrations of the upstream and tributary 

sections are 267 mg/L and 212 mg/L respectively for Event 2. The loading of tributary 
itself does not increase the CBOD5 concentrations to the observed levels downstream at 

WQTC02 of 433 mg/L. It is likely that the timing of Event 2 sampling "missed" the 

loading in the upstream and tributary sections and captured these loadings 

downstream. Regardless of cause of increase in CBOD5

In the forcing model, the CBOD

, this increase was accounted for 

in the "forcing," or second calibration method.

5 concentrations for the tributary contributions from the 

northern portion of Runway 34/16, WQTC05, were increased from the observed 

concentrations of 212 mg/L to 1,689 mg/L. The tributary concentration is calculated 

using the following formula:

where Q is the flow in cfs

C is the concentration in mg/L 

This forcing of the CBOD5 concentration is due to an increase in concentration along the 

creek. The incremental increase in CBOD5

The DO in Third Creek is a function of the carbonaceous deoxygenation rate, reaeration 

rate, photosynthesis/respiration, and the SOD. These rates are calibrated by using the 

data collected during Event 2 as discussed in the previous section. 

concentration was forced by increasing the 

tributary concentration and calculated using the mass balance described above. 

When the CBOD5 loading is increased because of adjusting the CBOD5

Figures for the aforementioned CBOD

loading from the 

tributary, there is additional oxygen demand. This oxygen demand depletes the 

available DO levels observed in the creek. The effect is seen where the DO 

concentrations in Third Creek are lower than the nonforced model.

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The sampling event data in the mainstem of Third Creek during LB2 shows an 

unexplained decrease in nitrate/nitrite at WQTC04. The concentrations of nitrate/nitrite 

observed at WQTC03 drop from 0.38 mg/L to 0.21 mg/L and 0.11 mg/L at WQTC04 

and WQTC06 respectively. The model was not able to capture this observed sharp 

decline in the creek without an extremely high nitrate/nitrite loss coefficient of 50 

(1/day) in Segments 3 and 4. Currently, there is no basis for this assumption. These low 

nitrate/nitrite levels likely do not have much affect on DO and calibrating to such a fine 

increment is not warranted.

and DO can be found at the end of this appendix.

For the third and fourth events, the Owens and Gibbs formula was appropriate for use; 

however, based on the velocities, depths, and ice observed in the field, the original 

values were multiplied by 0.5 and 0.2, respectively, to account for less reaeration due to 

ice cover. The Owens and Gibbs formula should also be used for depths greater than 0.4 

( )

Tributary

TC TC TC TC

Tributary Q

Q C Q C C 02 02 01 01 * − * =
feet and less than 11 feet and for velocities greater than 0.1 feet per second and 5 feet per 

second. The average depth observed in the field was below this range slightly. The 

average depth used in the STREAMDO model was 0.26 feet during LB3 and 0.25 feet for 

LB4, and the average velocity 0.22 and 0.24 feet per second, respectively. A calculated K2 

value of 109 was found for LB4. The calculated K2 is thus based on values slightly 

outside of the appropriate range for the equation. This is one of few equations available 

to calculate K2 for small streams such as Third Creek. As discussed previously, the 

calculated reaeration rate was multiplied by an "ice cover factor." Recommended factors 

range from 0.05 for complete ice cover to 1.0 for no ice cover. Depending on the extent of 

cover, reaeration values can be greatly reduced (EPA 1600/3-87/007, 1987).

K1, K3, K4, K5, and K6 were modified to match observed data assuming that instream 

concentrations vary slightly even after deicing loads pass through Third Creek. 

Following are the coefficient values used in the calibration effort for LB3 and LB4:

 K1 – 1.0 for LB3 and 2.3 and 1.3 for LB4

 K3 - 2.0

 K4 - 0.2

 K5 - 0.01

 K6 - 0.2

K1 was assumed higher for LB4 during the first segment because easily consumable 

materials could be broken down more rapidly than at the downstream locations. K3 and 

K4 were selected on the upper end of the recommended range based on observed data. 

K5 was assumed low based on lower pH and water temperatures noted during data 

collection. The K6 value selected is on the lower end of the recommended range based 

on instream temperatures and observed nitrate concentrations.

SOD was calculated using the following formula based on temperature (Chapra 1997):

S = S20 θ

where: S = 0.5

θ = 1.065

(T-20)

Discussion

This appendix contains the STREAMDO model output files for the two events (LB2 and 

LB4) that were chosen to bracket the seasonal aspects of runoff in Third Creek related to 

deicing activities. For LB2, the model observed versus model predictions were 

considered adequate, although the flow conditions were "forced" to match observed 

conditions. For LB4, the calibration effort was not as robust and observed CBOD5

concentrations were not matched sufficiently predicted CBOD5 levels, although 

observed DO concentrations matched predicted DO concentrations. The results of this 

modeling analysis suggests that a steady-state model is difficult to apply to the Third 

Creek system which experiences very dynamic runoff conditions and pollutant loads 

due to variability in conditions experienced throughout deicing season.