James Seppi CE394K Hydrology, Spring 2010 University of Texas.
HOWARD CHANG CE394K SPRING 2008 Detention Ponds & Bacterial Concentrations.
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Transcript of HOWARD CHANG CE394K SPRING 2008 Detention Ponds & Bacterial Concentrations.
HOWARD CHANG
CE394KSPRING 2008
Detention Ponds & Bacterial Concentrations
Introduction
Study Area: Round Rock, TXBrushy Creek is impaired for bacteria
Objectives
Bring Brushy Creek back into compliance
Put in detention ponds where needed
Hold water long enough for bacteria to die off
http://www.stormwatercenter.net/Manual_Builder/design%20examples/pond/title%20figure.gif
Approach
E. Coli data from TCEQ stations
Travel time from NHD plus flow data
Calculate decay rate
Size detention pond
Analysis
87200 34
2 201
90
Average E. Coli concentrations in org/100mL
Decay Rate12062 – 12060 0.144 /hr12060 – 12056 0.017 /hr
12069
12068
12062
12060
12056
342
Where to Place Detention Pond
87
200
342 20
1
Assume linear increase in bacteria concentration
12069 – 12068
12068 – 12062
Allowable conc = 126 org/100mLhttp://www.epa.gov/waterscience/standards/wqslibrary/tx/tx-wqs-20061215.pdf
12069 1206
8
12062 1206
0
mile
mLorg 100/1.58
mile
mLorg 100/3.25
1.94 mi
5.16 mi
3.22 mi
126 12
6
0
74
90<90
0
0.67 mi
2 mi
Sizing the Detention Pond
A decay rate of .144 takes 34 hours to reach 0Not feasible: too long & needs large storage
volume
ParametersDetention time 12 hrs brings 126 to 22Side slope 3:1Depth 6 feetWidth: Length 2:3Average flow 36 cfs inflow = outflow
Sizing the Detention Pond
Needed storage volume = 36 ac-ftDetention Pond dimensionsBase Top
Lo 604’ L 640’Wo 403’ W 439’
6.5 ac
Readjust Detention Pond Location
Next Steps Check locations Make sure it is suitable for
placing detention pond Add safety factor
87
200
342 20
1
12069 1206
8
12062 1206
0
0.67 mi
1.17 mi
126 12
6
22
96
22
112 <11
2
Summary
Place two detention ponds Storage volume of 36 ac-ft Detention time of 12 hours Reduces bacteria concentrations to 22 org/100mL
First pond 0.67 miles downstream of station 12069
Second pond 1.17 miles downstream of station 12068
Questions