HomeMy WebLinkAboutR-1996-116RESOLUTION NO. 116-96
FlRST SUPPLEMENT TO
FINAL STORMWATER ASSESSMENT RESOLUTTON
A RESOLUTION OF THE CITY COMMISSION OF THE CITYOF DANIA, FLORIDA, RELATING TO THE PROVISION OFSTORMWATER MANAGEMENT SERVICES; APPROVING AMITIGATION CREDTT POL|Cy; pROVtDtNG FORAPPLICATION OF THE MtTtcATtON pOLtCy; AND
PROVIDING AN EFFECTIVE DATE-
WHEREAS, the City Commission of the City of Dania, Florida, has adopted
Resolution No. 86-96, the Final stormwater Assessment Resolution, which imposed
Stormwater Assessments against property located within the City; and
WHEREAS' section 8 of Resolution No. 86-96 directed the city Manager to
develop and present a Mitigation credit Policy and any Stormwater Assessment
adjustments necessitated thereby to the City Commission; and
WHEREAS, the city's consulting Engineers developed a Mitigation credit policy
and computed all adjustments to the Stormwater Assessments necessitated thereby; and
WHEREAS, the City Commission desires to approve the Mitigation Credit policy
and to authorize and direct the city Manager compute any adjustments to the stormwater
Assessments necessitated thereby and present such adjustments to the city commission
for approval;
NOW, THEREFORE, BE IT RESOLVED BY THE CITY COMMISSION OF THE
CITY OF DANIA, FLORIDA, AS FOLLOWS:
SECTION 1.APPROVAL OF MITIGATION CREDIT POLICY. The Board
hereby approves the Mitigation Credit Policy attached hereto as Appendix A.
RESOLUTION NO. 116-96
sEcrloN 2. ADJUSTMENT oF STORMWATER ASSESSMENTS. The city
Manager is hereby authorized and directed to compute any adjustments to the stormwater
Assessments approved by Resolution No. 86-96 that are necessitated by the Mitigation
credit Policy. All such adjustments shall be presented to the city commission for approval
and may be included on the consent agenda. Upon approval of the adjustments by the
city commission, the city Manager is hereby authorized to refund an amount equal to the
difference to any property owner presenting a receipt for payment an ad valorem tax bill
that includes the unadjusted Stormwater Assessment.
SECTION 3. CONFTRMATTON OF RESOLUTTON NO. 86-96. Resotution
No. 86-96, as heretofore amended, is hereby ratified and confirmed.
SECTION 4. EFFECTIVE DATE. This Resotution shail take effect
immediately upon its adoption, this 26th day of November, 1996.
PASSED AND ADOPTED on the 26th day of November, 1996.
THE IA, FLORIDA
(SEAL)
By
J rtino
ayor - Commissioner
ATTEST:
Marie J. Ja
City Clerk - Auditor
Approved for Form and Correctness:
, 4"-,^"-1, e- dtt^
2
By
Frahk e . AdTer, City Aitorn6y
RESOLUTION NO. 116-96
APPENDIX A
CIry OF DANIA
STORMWATER UTIL]TY MITIGATION CREDIT POLICY
MITIGATION
CREDIT POLICY
FOR
CITY OF DANIA
Prepared by:
berru&col
ENGTNEERS f suptrEYons
VlJlin".
PIANNERS
2 Oakwood Boulevard, Suite 120
Hollywood, Florida 33020
B&C ProJect No. 96-1507.901
Date Submitted October 14, '1996
1904
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Mitigation Credit Policy 1
INTRODUCTION
The City of Dania has determined that stormwater mitigation credit can be
determined based on the stages generated by a 10 year - 't day storm event and the
volume of water discharged from a property during a 25 year - 3 day and 100 year -
3 day storm event. The three storms have been used by the city of Dania as the
basis of the stormwater mitigation policy because of requirements stipulated by the
South Florida Water Management District (SF\ JMD) in the Basis of Review for
Surface Water Management Permit Application. The computation of the stages
produced and volume of water discharged by a property during these storm events
will be the responsibility of the property owner and must be presented to the City of
Dania to determine the credit.
CREDIT CRITERIA
By complying with the 10 year - 1 day storm event criteria, one is eligible for a 37Yo
credit, the 25 year - 3 day event criteria, one is eligible for an additional 31% credit
and by complying with the 100 year - 3 day event criteria, one is eligible for another
32Vo qedit which results in a total of 100% credit. These percentages were
computed by analyzing the total runoff produced by each of the three storm events
for the curve numbers listed in Technical Release 55, Urban Hydrology For Small
Watersheds 2tu Edition, published by the United States Department of Agriculture.
The maximum amount of direct runoff which can be produced by any of the three
design storm events is that which is produced by the 100 year - 3 day event. Based
on this total, percentages were computed for the initial runoff produced by the 10
year - 1 day event as well as the excess runoff generated by the 25 year - 3 day
event and the 100 year - 3 day event. These percentages were computed for each
bcrrv&colvin*rl6!{6rffi Plr,{s
Oclober 14, 1996
B&C Proiecl No 9G1507.901
Mitigation Credit Policy 2
curve number listed in Technical Release 55 and subsequently averaged to produce
the credit percentages which a property owner will be eligible to receive. Table 1
reflects the computation of the percentages allocated to each storm event.
TABLE 1
S = Potenrial Maximum Retention t CN
tfier Rurcff Begiw (iz) =
-
- tO
P = Rainfall (in)
( P - 0.2S)2
Q = Runolf in) = ip.,i8s)
R. .. =, €u-" , , 166
Q ron-r,
o"..-R,r-r, =( R,o-ro ) x 100
Vrcotz
o,*., = (* - Rrr-r, .i,o-,. ) x 1oo
Curve
Number
S
(in)
P ,o-ro
(in)
Q,o-ro
(in)
P rr.r,
(in)
Qrr-r,
(in)
D| 1oa-72
(in)
Q,oo-r,
(in)
Percent
lnitial
Runoff
R,o-r.
Excess
Ru noff
Rrr-r,
Excess
Runoff
R,oo,r,
40.00
45.00
50.00
55.00
60.00
65.00
70.00
75.00
80.00
85.00
90.00
95.00
98.00
15.00
12.22
10 00
8.'t 8
6.67
5.38
4.29
3.33
2.50
1.76
I It
0.53
0.20
1 .97
2.58
J.Z I
3.85
4.50
5.14
5.78
o..t I
7 .04
7 .67
8.29
8.90
9.26
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
14.70
19.70
19.70
19.70
19.70
19.70
'19.70
19.70
'19.70
19.70
19.70
19.70
19.70
19.70
22Yo
76Yo
28Yo
31Yo
33o/o
36%
38Yo
4Oo/o
41%
43%
45o/o
47%
48Yo
360/o
35Yo
34o/o
34%
33'/.
32%
31Yo
30%
30%
29Yo
28%
27Yo
27%
42%
39%
37%
35%
340
32%
30%
29%
28%
27o/o
26!o
26Yo
Total 37%31Yo 32Yo
lreruy*ss October 14. 1996
B&C Project No 96-1507.901lvin*
9.50
9.50
9.50
9.50
9.50
9.50
9.50
9.50
9.50
9.50
9.s0
9.50
9.50
5.'13
6.14
7.11
8.03
8.92
9.76
'10.57
11 .34
12.07
12.78
13.45
14.09
14.46
8.80
10.10
1 1.3'1
12.43
13.48
14.45
15.35
16.20
16.99
17 .73
18.43
19.08
'19.46
Mitigation Credit PolicY J
MITIGATION POLICY
The required stages generated by a 10 year - 1 day, 25 year - 3 day and 100 year -
3 day storm event in each basin is indicated in Table 2.
TABLE 2
STORM
EVENT
BASIN
NUMBER
MAXIMUM
STAGE
(ft)
BASIN
AREA
(ac)
STORAGE
VOLUME
(ac-ft)
1O YEAR
1 DAY
1 5.66 326.57 1848.39
2 5.27 1105.95 5828.36
92.04 492.41
4 5.43 694 69 3772.17
5A 5.14 261.99 1346.63
5B 5.23 425.39 2224.79
5C 5.81 290.00 1684.90
25 YEAR
3 DAY
1 6.44 326.57 2103.11
2 EO?1105.95 6558.28
J 5.73 92.04 527 .39
4 aoo 694.69 4161.19
5.56 26'1.99 1456.66
5B 5.94 425.39 2526.82
JU 6.65 290.00 1928.50
1OO YEAR
3 DAY
1 7 .07 326.57 2308.85
2 o.c I 1 105.95 7199.73
o_z+92.O4 574.33
6.54 694.69 4543.27
5A 6.09 261.99 1595.52
5B 6.55 425.39 2786.30
5C 7 .34 290.00 2128.60
The policy recommends that each owner submit an application demonstrating
compliance with the following criteria:
Lcrrv&colvin*Ell<*6r,ft\c qlrc
Oclober 14 1996
B&C Pro,eci No 96-1507 901
4
Mitigation Credit Policy 4
10 YEAR. 1 DAY STORM EVENT
The total mitigation credit which can be obtained by complying with the following 10
year storm criteria is 37o/o of Ihe amount assessed to the property owner.
A. The property in question will receive a 37% mitigation credit if the computed
stage for the 10 year - 1 day storm event is less than or equal to 10 year flood
elevation Allowed by Broward County (see attached map).
B. The property in question will receive a 0% mitigation credit if the computed stage
for the '10 year - 1 day storm event is greater than the10 year flood elevation
allowed by Broward County (see attached map).
25 AND ,IOO YEAR. 3 DAY STORM EVENT
The total mitigation credit which can be obtained by complying with the 25 year
storm criteria js 31 % and 32Yo tor complying with the 100 year - 3 day criteria. This
criteria is based on the volume of water a property discharges to the city storm
sewer system as a result of the 25 and 100 year event. The volume of water
discharged is computed by following Table 3. The computed stage is calculated by
the applicant, the average site grade is provided by the applicant, the feet of rainfall
is computed by calculating the difference between the computed stage and the
average site grade or control elevation, the site area is also provided by the
applicant and the volume is computed by calculating the product of the site area and
the feet of water stored. The required volume is computed in the same manner for
the exceptidn that the required stage is obtained from Table 2 for the basin in
question. The percent of computed volume discharged above the required volume
is calculated. Finally a direct percent credit is applied. For example, given a 25
year event in which the computed volume is 10% above the required volume' the
barrv8colvin*Mi6rrc 't,,{s
October 14. 1996
B&C Projecl No 96-1507.901
Mitigation Credit Policy 5
property owner will receive 90% of the total 317o possible for the 25 year - 3 day
event.
@ : 25 and lN year computed stage (to be provided by applicant).
@ = Average Site Grade (to be provided by applicant).
@:O-@
@: Total Site Area (to be provided by applicant).
@:@*@
@ : 25 and 100 year required stage (from table 2).
@:@-@
@=@*@
If @ > @, no discharge, 100% credit for 25 and 100 year.
If @ < @, dir;charge, ffedit for 25 and 100 year will be based on excess discharge above
required volume @.
COMPUTED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
@ o @ @
REQUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REQUIRED
VOLUME
(ac-ft)
a,@ @ @ @
bcrruEcolvin*rl<E6rll4t6 Pi/Jtq
Oclober 14. 1996
8&C Proiect No 96-'1507.901
TABLE 3
o
Mitigation Credit Policy tl
MITIGATION CREDIT EXAMPLES
The following examples illustrate the application of the policy
Example number 1:
A 10 acre residential site located in basin 4 has the following computed stages:
10 Year 1 DaY = 5.75' NGVD
25Year 3 DaY = 6.90' NGVD
100 Year 3 Day = 7.25' NGVD
Average Site Grade = 5.50' NGVD
From Broward County Flood Maps:
10 Year 1 DaY = 6.00' NGVD
'100 Year 3 Day = 7.00' NGVD
The Required Stages from Table 2:
10 Year 1 DaY = 5.43' NGVD
21Year 3 DaY = 5.99' NGVD
100 Year 3 Day = 6.54' NGVD
10 Year 1 Dav Credit Requirements:
ls Computed Stage greater or less than Broward county 10 year 1 Day Flood
Stage:
Computed Stage of 5.75' < Broward County Flood Stage of 6.00'
Therefore 37% credit. since the '10 Year reouirement is met
bcrrv&col Oclober 14, 1996
B&C Proiect No 96-1507.901vrhtu
Mitigation Credit Policy 7
Since the computed volume is greater than the required volume, the excess
volume of (14.00-4.900) 9.10 ac-ft will be discharged from the site. The
excess volume is approximately ([9.10/4.90f100) 185% of the required
volume,Therefore 0%it. since the 25 Year requirem ent is not met.
Since the computed volume is greater than the required volume, the excess
volume of (17.50-10.40) 7.10 ac-ft will be discharged from the site. The
excess volume is approximately ([7.10/10.40f100) 68% of the required
COMPUTED
STAGE,
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
6.90 5.50 1.40 10.00 14.00
REQUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REQUIRED
VOLUME
(ac-ft)
5.99 5.50 0.49 10.00 4.90
COMPUTED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
7.25 1.75 10.00 17.50
REQUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REOUIRED
VOLUME
(ac-ft)
6.54 5.50 1.04 '10.00 10.40
bcnv&colvin,*rlr:.{Brwlrs Pl}Jts
October 14, 't 996
B&C Project No 96-1507.90'l
25 Year 3 Dav Credit Requirements (usinq Table 3):
100 Year 3 Dav Credit Requirements (usino Table 3):
5.50
Mitigation Credit Policy
TOTAL CREDIT FO THIS SITE 37o/o H0 Year) + 0o/o /25 Year + 10o/. (100 Year)
Example number 2:
A 25 acre commercial site located in basin 2 has the following computed stages
10 Year 1 Day = 5.05' NGVD
25 Year 3 Day = 6.00' NGVD
100 Year 3 Day = 6.40' NGVD
Average Site Grade = 5.00' NGVD
From Broward County Flood MaPs:
10 Year 1 Day = 6.00' NGVD
100 Year 3 Day = 7.00' NGVD
The Required Stages from Table 2:
'10 Year 1 Day = 5.27'NGVD
2lYear 3 Day = 5.93' NGVD
100 Year 3 Day = 6.51' NGVD
10Y rl DavC it Reouire ts:
ls Computed Stage greater or less than Broward county 10 year 1 Day Flood
Stage:
Vll'1rc!,suy*esl
october 14. 1996
B&C Project No 96-1507.90',1
B
volume, Therefore ([1 00-68].32l100) 10% credit. since the 1 00 Year
reouirement is partiallv met.
= 47o/o
Mitigation Credit Policy o
Computed Stage of 5.05' < Broward County Flood Stage of 6.00'
Therefore 37o/o credits tn cet OYear urremene1reo t is met
Since the computed volume is greater than the required volume, the excess
volume of (25.00-23.25) 1.75 ac-ft will be discharged from the site. The
excess volume is approximately (11.75123.25f100) 7.5o/o ol the required
volume, Therefore ([100-7.51*31/100) 29% credit. since the 25 Year
reouirement is oartiallv met.
COMPUTED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
6.00 5.00 1.00 25.00 25.00
REOUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REQUIRED
VOLUME
(ac-ft)
5.93 5.00 0.93 25.00 23.25
COMPUTED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
6.40 5.00 1.40 25.00 35.00
REQUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REQUIRED
VOLUME
(ac-ft)
6.51 5.00 1.51 25.00 37.75
bcrrvtcolvin'.rN416rffi PLr,te
Odober 14, 1996
B&C Proiecl No 96-1507.901
25 Year 3 Day Credit Requirements (usino Table 3):
100 Year 3 Day Credit Reouirements (usinq Table 3):
Mitigation Credit Policy 10
TOTAL CREDIT FOR TH IS SITE 370/0 (1 Yearl + 29o/o (25 Year) + 32o/o ('t 00 Year)
= 98o/o
A 50 acre i'esidential site located in basin 5C has the following computed stages
10 Year 1 DaY = 6.10' NGVD
25 Year 3 Day = 6.75' NGVD
100 Year 3 Day = 7.25' NGVD
Average Site Grade = 5.75' NGVD
From Broward County Flood Maps:
10 Year 1 DaY = 6.00' NGVD
100 Year 3 Day = 8.00' NGVD
The Required Stages from Table 2:
10 Year 1 Day = 5.81'NGVD
25 Year 3 DaY = 6.65' NGVD
100 Year 3 Day = 7.34' NGVD
ls Computed Stage greater or less than Broward county 10 year 1 Day Flood
Stage:
kruy*ssl"i**October 14 1996
B&C Project No 96-1507 901
Since the computed volume is less than the required volume, fherefore 32%o
credit. since the 100 Year reouirement is met.
Example number 3:
10 Year 1 Day Credit Requirements:
Mitigation Credit PolicY 11
Computed Stage of 6.10' > Broward County Flood Stage of 6.00'
Therefore 0% credit. since the 10 Year reouirement is met.
COMPUTED
STAGE
(ft)
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft)
6.75 1 50.00
REQUIRED
STAGE
(ft)
AVERAGE SITE
GRADE
(fr)
WATER
STORED
(ft)(ac)
REQUIRED
VOLUME
(ac-ft) _
6.65 5.75 50.00
COMPUTED
STAGE
ft
AVERAGE SITE
GRADE
(ft)
WATER
STORED
(
SITE AREA
(ac)
COMPUTED
VOLUME
(ac-ft
1.50 50.00 75.007.25
REQUIRED
STAGE
ft
AvrRRce sre
GRADE
(ft)
WATER
STORED
(ft)
SITE AREA
(ac)
REQUIRED
VOLUME
ac-ft)
7.34 E -'E 1.59 50.00 79.50
bcrv&colvin*rirx$rwr\s Fl,M
October 14, 1996
B&C Project No 96-1507.901
25 Year 3 Dav Credit Requirements (usinq Table 3):
since the computed volume is greater than the required volume, the excess
volumeof(50.0045.00)5.ooac-ftwillbedischargedfromthesite.The
excess volume is approximately ([5.00/45.001100) 11.0o/o of the required
volume, Therefore ff100-1 1l-31/100) 27.5% credit' since the 25 Year
reouirement is Partiallv met.
100 Year 3 Dav Credit Requirements (usinq Table 3):
50.005.75
SITE AREA
45.000.90
5.75
Mitigation Credit Policy 12
!*..*y*rslrrlm
October 14. 1996
B&C Project No 96-1507.901
Since the computed volume is less than the required volume, Therefore 32%
credit, since the 100 Year requirement is met.
TOTAL CREDIT FOR THIS SITE = 0% (10 Year) + 27.5% (25 Year) + 32% (100 Year)
= 59.5%
Mitigation Credit Policy 13
10 YEAR FLOOD ELEVATION MAP
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October 14, 1996
B&C Proiect No 96-1507.901
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