FINAL PLAT: ARROYO NORTE UNIT 4 CASE NUMB - S2006015 ARROYO NORTE.PDF

Report to the Board of Supervisors
Prepared by the Maricopa County Planning and Development Department
Commission Hearing Date: September 6, 2007
Board Hearing Date: September 3, 2008 (Continued from August 20, 2008)
Case: 52006015 - Arroyo Norte Unit 4
Agenda Item: 3
Supervisor District: 3
Applicant: Hoskin Ryan Consultants
Property Owner: Pulte Homes
Request: Final Plat in the R1-7 RUPD zoning district
Existing On-Site and Adjacent Zoning:
On-site: R1-7 RUPD PAD (Z2002092)
North: R1-8 RUPD PAD / Arroyo Norte Unit 5 and R1-10 RUPD
PAD / Arroyo Norte Unit 6
East: R1-18 RUPD PAD / Arroyo Norte Units 8 - 10
South: R1-6 RUPD PAD / Anthem Unit 21-A
West: R1-7 RUPD PAD / Arroyo Norte Unit 3 (City of
Phoenix)
Proposed Use: 100-lot, 4-tract, single-family residential subdivision
Site Location: East of 1-17, south of Circle Mountain Rd. (in the
Anthem area)
Site Size: Approx. 38.6 gross acres
Proposed Density: 2.59 d.u./ac.
County Island
Status: N/A
Summary of Conformance with Adopted Plans:
County Plan: The County Area Plan designates most of the site for
Large-Lot Residential (1-2 d.u./ac.) uses, but allows for
Scenic Commercial uses along the highway frontage.
The proposal is, arguably, in concert with the County

Area Plan because of allowance for increased density
for preservation of open space connections to Gavilan
Peak determined at time of Arroyo Norte's zoning
entitlement.
Municipal Plan: N/A
Support/Opposition: There is organized neighborhood opposition to the Arroyo
Norte development project, but no written opposition has
been provided specific to this Final Plat since there has
been no related public notice and none is required for a
Subdivision case with approved Zoning.
Discussion: The Preliminary Plat was first approved by the Planning & Zoning
Commission on August 11, 2005 (S2004107). It was subsequently
extended on August 3, 2006 (S2006048) and September 6, 2007
(S2007044). The current Preliminary Plat will expire on September
6, 2008. If the subject Final Plat is not recorded prior to that date,
the Preliminary Plat will expire. Further, conditional zoning approved
under case Z2002092 will also be positioned for revocation.
The applicant has complied with ARS 9-474, as amended in 1978, by
routing a copy of the final plat to the all municipalities within three
miles of the subject property and to all intended utility providers.
There were no objections to the request raised by any of these
entities. A Certificate of Assured Water Supply from Arizona
Department of Water Resources is also included.
All requirements of the Maricopa County Department of
Transportation, the Maricopa County Environmental Services
Department, and the Flood Control District of Maricopa County have
been met. All agencies have signed-off on the final plat; however,
issues regarding Drainage Review remain outstanding on the
associated Infrastructure Permit (B200603115).
On August 14th the applicant submitted revised improvement plans.
On August 18th the applicant was provided with Drainage Review
comments (attached). If the applicant makes a resubmittal that
adequately addresses these drainage design issues prior to the
September 3rd BOS meeting, staff will recommend approval of the
final plat.
Staff
Recommendation: Continue indefinitely

Planner: Robert Kuhfuss, AICP, Senior Planner
Reviewed by: Darren V. Gerard, AICP, Deputy Director
Attachments: Case and vicinity maps (2 pages)
Final Plat (6 pages, reduced 8.5" 11")
Letter from the applicant (1 page)
ADWR Certificate of Assured Water Supply (1 page)
Drainage Review comments (3 pages)
Enclosure: Final Plat Mylars

MARICOPA COUNTY, ARIZONA
Drawn By:;1/ 07/18/2008 Legal Description: N2 Section: 10 Township: 06N 02E
Applicants Name: ANTHEN ARIZONA, LLC Phone: * Zoning Map
Case Address: * Parcel: A103• S2006015
SUPERV1SORAL. DISTRICT NO. 3
REQUEST:
ARROYO VISTA UNIT 4
subs2006 FINAL PLAT
R1-7 R.U.P.D. / PAD. ZONING DISTRICT
Streets
(39.58 ACRES)
j Zoning
- Thruway
„ PLANNING , mApjcopA a, DEVELOPMENT couNry _
PI-10ENIX, ARIZONA

MARICOPA COUNTY, ARIZONA
Drawn By: DWI 0711812008 I Legal Description: N2 Section: 10
Applicant's Name: ANTHEN ARIZONA, LLC Zoning Map
Case Address: * Parcel: • ji,103 82006015
SUPERVI, ,OVAL. DISTRICT NO. -3
REQUEST:
ARROYO VISTA UNIT 4
FINAL PLAT
R.U.P.D. / P.A.D. ZONING DISTRICT
(39.58 ACRES)
MAIIICOPA COUNTY 1 - 2 500 '
PLANNING & DEVELOPMENT
PHOENIX, ARIZONA

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y
yan liGnsultan.ts
„noire edgineering sOlutiOns -
Board of Supervisors
Maricopa County Planning & Development
501 N. 44" Street
Suite 200
Phoenix, AZ 85008
RE: Arroyo Vista
Gentleman:
•We are designing a residential subdivision named Arroyo Vista located on
roughly 157 acres at Circle Mountain Road and Gavilan Peak Parkway, located
within Maricopa County.
The owner of this property is Pulte Homes Corporation, located at 15.111 N. Pima
Rd., Scottsdale, AZ 85260.
The engineer on this project is Hoskin Ryan Consultants, Inc., 201 .W Indian
.School Rd„ Phoenix, AZ 85013 -
Letters have been addressed to cities within three miles of the plat Letters have
been enclosed in submittal package.
If you need any additional information or have any questions, please feel free to
contact me at 602-252-83M.
Ted A. Luther,
Sr. Project Manager
TLJdk
En MAY 19 MU
82.006
G6031
•201 West Indian4hool Road, Phoenix, AZ 85013:3203 I Office: (602) 252.8384 I Fax: (602) 252.8385 I wwwthoskinrYan.com
Land Planning I Hydrology I Land Development I Civil Infrastructure I SUrveyjng I Construction Services I Graphic Services

This is to certify that
rporation, a NU
hits met the A.R.S. §§ 45-576 and the appli e. . F
By powers of the Arizona Department of by the
S of Arizo to the conditions contained in the ations,
GS
S iii dent water of will be continuously available t
the referenced ones so years. The referen
• 291 lots as describ plat on file with the Dep
water U • of 25 per year. The subdivision will be
Project water and water leased from the Ak-Chin.
American Water Company.
invalid as to any entity not nem
be assi pursuant to A.A.C.
NA DEPAR I NT OF WATER RESO CES

Maricopa County
Planning & Development Department
111111M111111111111111111111111M1
William Haas, P.E.
Planning eic Development
501 North 44 th Street, Suite 200 Date: August 18, 2008
Phoenix, Arizona 85008
Phone: (602) 372-4114
Fax: (602) 506-8762 Memo To: Darren Gerard, Deputy Director, Department of Planning &
wwwrnaricopa.gov/planning address: Development
WilliamHaas@mail.maricopa.gov
Attn: Robert Kuhfuss, AICP, Senior Planner, Project Management Division
From: William Haas, Drainage Engineering Supervisor, Planning and
Development
Subject: B200603115, Arroyo Norte Improvement Plans
The plans and reports submitted 8/14/08 for permit # B200603115 have been
reviewed and the following comments require resolution. Please note that all
comments are typical only due to the compressed timeframe for the review. The
engineer must evaluate all comments as they pertain to other portions of the design
not specifically mentioned in this review. The associated Final Plat, S2006015, was
not submitted concurrent with this latest review and is not recommended for approval
by the Board of Supervisors.
Drainage Report
1. As noted in the previous review comments, the design of bleed-off systems
should conform to standard 6.10.10 of the County standards manual. This
section identifies that "the maximum bleed-off rate should typically not
exceed 1 cfs." The engineer has identified an average rate of 1.5 cfs for basin
B west + B central and 2.26 cfs for basin A. Correct the design to meet the
standard.
2. The outfall of retention basin in Tract C (B central) is listed a 1905.84. The
contours show the existing grade as greater than 1910. How can this be
physically installed without grading into the restricted NAOS area? Verify and
correct the design.
3. The adjacent water surface elevation for Tract C is 1911+, as shown on the
plans. Placing a bleed-off pipe at this location has the effect of bring off-site
storm water into the basin through the pipe. Correct the design.
4. As previously requested, it is required that the engineer provide a discussion
on modeling analysis and parameter selection. The calculation of the bleed-off
rate uses the orifice equation without providing any discussion. Several
discrepancies are noted in the modeling.
a. The flow coefficient is selected as 0.6. This is applicable for smooth
edged openings. However, for rough-edged opening, as might be cut
by a contractor in the field using a torch or other means, 0.4 is

recommended. Why is 0.6 selected? The engineer has not provided any
construction specifications on the plans that would dictate a smooth-
edged opening. Discuss and justify the parameter selection in
conformance with the design.
b. The average headwater depth for basin A is given as 1.13 feet for a 9
inch orifice opening. This can be assumed to be half the basin depth of
3 feet minus the opening height (2.25/2 = 1.125 feet). However, for
free flowing outlet conditions, as should be the design, the headwater
depth is measured from the center of the orifice opening. Correct the
modeling.
c. The analysis utilizes an average flow rate calculated at the average
depth. However, the orifice equation is exponential and not linear. The
average flow rate will not occur at the average depth. The County
standards manual in section 6.10.10 dictate the use of the Modified
Puls storage routing method (as utilized by Hec-1) to facilitate design
to address this specific issue. Correct the modeling.
5. The HEC-1 model identifies that retention in basin 6 is based upon mass
grading and not the 100-year 2-hour requirement. As the mass grading is not
currently approved this is inappropriate. There are no restrictions upon this
basin that would require that the excess volume be maintained. Either place
such restrictions through plat notes or revise the modeling to reflect regulatory
required storage.
6. The HEC-1 developed conditions model appear to have basin B identified as
basins 1 and 2 in the provided DEI map (figure 3). The model identifies that a
25 foot weir is assumed while a 30 foot weir is designed. Correct this
discrepancy and the modeling.
7. The report identifies that wash A has a existing condition flow of 2,523 cfs
and post development flow rate of 2,159 cfs. The models identify that the
flow rate is 2,528 at C7A5c and 2,519 at C75Ac8. These rates are shown on
figures 3 and 4. Correct these, and all other, typographical errors.
8. Table 6 shows the drainage area for Basin B as 30.02 ac which equals 0.469
sq. mi. Basins 7A5h1 and 7A5h2 have a combined area of .0413 sq. mi or
26.43 ac. Additionally the volume modeled does not match the volume
provided as shown in table 6 or appendix B. Explain why this modeling does
not reflect the design.
9. As previously noted, the HEC-1 analysis used to evaluate the pre and post
construction hydrology for the site utilizes a minimum time step of 5 minutes
for calculations. For the most of the identified routings, this is longer than is
appropriate for the physical length of the route at the identified velocities. This
artificially attenuates the peak flow at the end of the route. In conjunction with
the proposed bleed of system, this may represent an adverse impact to down
stream properties in violation of the Drainage Regulation. The engineer's
response in the August 13 HRC memo is not accurate. Any time that a routing
time, as represented by the NSTPS and TMIN, models a time greater than

what is physically present, it artificially moves the hydrograph. As previously
requested, revise the modeling to accurately reflect and model the watercourse
geometry.
10. As noted in previous reviews, the Froude number for artificial channels should
be maintained below 0.86. Wash A is not in conformance with this standard at
several sections. The engineer's response in the August 13 HRC memo is not
accurate nor is the analysis mentioned provided in this report.
a. Reducing the Froude number in some sections is not a justification for
increasing it at other sections.
b. Based on modeling performed by County staff utilizing the HRC
modeling provided; when additional conveyance is added, the model
does calculate the Froude number as stated by the engineer. However,
the warnings generated by the model indicate that the model is not
properly resolving the equations and defaulting to a base parameter.
When additional cross sections are added, as recommended by the
HEC-RAS user's manual, the equation is properly resolved and the
channel hydraulic characteristics meet County standards. Therefore, a
reduction in the encroachment limit on wash A is warranted. Verify
and revise the design accordingly.
Sincerely,
William Haas, P.E.