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RESOlUTION M0. 76-135
A RESOLUTION OF THE CITr COUtICII OF THE CITY OF PALM DESERT,
CAIIFORNIA. RATIFYIMG THE EXECUTION OF A PROFESSIONA� SERYICES
CONTRACT MITH HOUSLEr/MtLIDAN ASSOCiATES
1AIEREAS. the Citr has experienced three storms in less than t�+o months
,A,1�h �reated da�aage to public and private prope�ty r+hich could have been sub-
stanti�lly reduced or ellminated by an adequate storm Grain system; and
MHEREAS. the City has previously ca�aissioned Housley/Hilldan to update
the City's Master Drainage Plan; and
WHEREAS, Federal Funds in an amount up to 55.000,000 may be available
for finanting a stpr� Arain system under the Public Works Employ+nent Act of
1976; and
MHEREAS, the expeditious filin9 of the application for those funds was
consldered necessa�y; and
WHEREAS, the City Cou�cil did approve in principle the hirinq of
Housley/Milldan Associates at the re9ular meeting of October 14, 1976, to
prepare the necessary applfcation. plans. and specifications; and
MHEREAS. the Mayor anG City Clerk have executed a contract Nith
Housley/Milldan Associates on behalf of the City which has been included in
the application for funds submitted to Economic Developme�t fWminist�ation.
NON. TNEREFORE. BE IT RESOLVEO that che City Councit of the Cicy of
Palm Desert does resolve as follows:
1. That the above recitations a�e true and co��ect, and
2. That the contract as executed is approred, and
3. That the action taken by the Ma�ror and City Clerk is hereby
ratified. and
4. That the attached revised pa9e 1 be inserted in the contract.
(Exhibit A)
PASSEO, APPROYED, aod ADOPTED on tfiis 28th day of October, 1976,
by the follo+iing vote:
ArES: McPherson, Mullins, 1lewbrander a Brush
NOES: NOne
IIBSEMT: Seidler
ABSTAIN: None
AITEST;
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(e)
,...... �. � .,
alerts. eta. for tise directly chargeable to
the proj�at= plus une�ployoent. exise and payroll
tuces; and con�ributions for Social Securit�.
eaplorent coo�pensation inaurances, retirement.
•edical atd insurance benefits.
(3) Indirect costs as compensation for overhead as
defined b� ASCE 2ianual No. 4S. Compensation for
salar� costs and indirect costs� aa defined in (2) and
(3) above, shall be made at a rate of 1.20 times the
direct payroll cost. Justification of said rate is
attached aa Exhibit "D".
In addition to said payroll. aalary and indirect costa
of work performed br ENGINEER's personnel. ENGINEER shall
be paid a fixed profit of $3,000.00. If the total amount
of billable payroll salary and indirect costs is less
than $40,000. said fiaed profit shall be reduced in
direct proportion �rith such decrease.
The costa of �rork done by the ENCINEER's subcontractors
ahall be reimburaed to the ENGINEER, plus an amount of
0.15 times such aubcontract costs.
Payment of allowable costs and a pro rata portion of the
fixed profit shall be made monthly to ENGINEER based
upon invoices prepared by ENGINEER in accordance with
its atandard practice.
Ia addition to the fees set forth above, ENGINEER shall
be reimbursed for necessarily incurred expenses as
follays:
(1) Reproduction and printing performed by subcon-
tractor ahall be billed at cost plus 10�.
(2) I,ons distance phone calls made by the ENGINEER
to numbers outside of Riverside County and
Orange Count� shall be billed at coat.
(3) Other identifiable, job related expenses which
have received prior approval of the CITY shall •
be allaved md shall billed at direct coat.
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Willdan Associates
Engineers, Architects & Planners
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DRAFT
MASTER PLAN OF DRAINAGE
NORTH PALM DESERT AREA
City of Palm Desert
April, 1979
WI LLDAN ASSOCIATES
74-075 EI Paseo, Suite A-2
Palm Desert, California 92260
(714) 568-5641
(714) 824-2143
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May 8, 1979
City of Palm Desert
45275 Prickly Pear Lane
Palm Desert, California 92260
Attention: Mr. Clyde Beebe
Director of Public Works
Subject: Master Plan of Drainage
North Palm Desert Area
Dear Mr. Beebe:
The enclosed report summarizing our studies of drainage requirements for
the North Palm Desert area is submitted in accordance with our contract with
the City dated November 9, 1978.
The report documents the study effort associated with the development of a
master drainage plan for the portion of the City's sphere of influence lying
northerly of the Whitewater River. The Master Plan describes a comprehensive
program for the development of drainage facilities and presents alternative
facility plans designed to meet the needs of the community. The total cost of
the recommended program is estimated to be $15,200,000. The amount includes
allowances for technical, legal and administrative costs, as well as a factor
for construction contingencies.
We wish to express our appreciation to you, Mr. Paul Williams and the members
" of your staffs for the cooperation and assistance rendered us during the investi-
"� gation. We must also acknowledge the numerous other cities, agencies, and
individuals whose cooperation contributed greatly to the study.
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City of Palm Desert
Mr. Clyde Beebe
'�" May 8, 1979
Page 2
We are available to discuss the contents of this report with you and look
forward to assisting the City further in the implementation of its recom-
mendations .
Respectfully submitted,
WI LLDAN ASSOCIATES
Gene B. Scothorn, P. E.
Vice President
GBS/jk
Enclosure
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TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION
,,,, 1.1 Authorization and Scope
1.2 Description of the Study Area
1,3 History of Drainage
1.4 Conclusions and Recommendations
CHAPTER 2 STUDY APPROACH
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2.1 Existing Drainage Patterns and Facilities
2.2 Flood Frequency
2.3 Methodology
�++' CHAPTER 3 TECHNICAL STUDY
3.1 Hydrologic Studies
3,2 Coefficient of Runoff
3.3 Rainfall Intensity
�, 3.4 Planned Use
3.5 Limitation of Stormflow from Developments
3,6 Hydraulic Studies
3.7 Retarding Basins
" CHAPTER 4 PROPOSED MASTER PLAN SYSTEM
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4, 1 Identification of System Elements
4.2 Drainage Area Designations
4,3 Description of the Proposed Drainage System
4, 4 Alternative Systems
�' 4.5 Priority Schedule
4,6 Regional Drainage Facilities
4.7 Areas SusceptiblP to Inundation
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TABLE OF CONTENTS, continued
Pag e
CHAPTER 5 ESTIMATED COST OF MASTER PLAN
� I MPLEMENTATION Z$
5.1 Basis of Estimates 2$
5.2 Estimated Project Costs 30
5.3 Project Cost of Alternative Systems 31
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'�` CHAPTER 6 FUNDING METHODS 32
6.1 General Fund 3Z
6.2 Drainage Fees 32
6.3 Federal/State Assistance Program 35
av 6.4 Assessment District 35
6.5 Combinations of Funding Methods 36
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Tabie
4-1
4-2
5-1
5-2
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6- 2
LIST OF TABLES
Facility Identification Codes
Suggested Priority Schedule For Recommended
Facilities Plan
Estimated Project Cost of Recommended
Drainage Plan
Estimated Basin Costs For Recommended
Drainage Plan
Drainage Costs Associated With The Recommended
Facilities Plan
Potentially Collectable Drainage Fees
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Figure
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LIST OF FIGURES
Description
Major Drainage Basins
Conveyance Faci I ities
Drainage Areas
Recommended Plan (Alternative "A")
Alternative Plan (Alternative "B")
Construction Cost Indices
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CHAPTERI
I NTRODUCTI ON
1.1 - Authorization and Scope
In November 1978 the City of Palm Desert authorized Willdan Associates
to develop a Master Plan of drainage for those portions of the City's sphere
of influence lying northerly of the Whitewater River Stormwater Channel. The
purpose of the authorization was to provide a comprehensive, long-term program
for the development of adequate drainage facilities to serve the area. The study
area extends from Interstate Highway 10 on the north to the Whitewater River
Stormwater Channel on the south and from Monterey Avenue on the west to
approximately 1/4 mile easterly of Cook Street on the east. The scope of the
investigation was intended to provide the City with a means of coordinating
drainage aspects of pending developments and a mechanism for evaluating the
impact of stormwater runoff within the study area. One major premise of the
Master Drainage Plan was the incorporation of land use criteria proposed in the
General Plan Amendment presently under consideration by the City.
1.2 - Description of the Study Area
The study area includes some 9 square miles of highly variable desert
terrain extending from Interstate 10 on the north to the Whitewater River Storm-
water Channel on the south .
While the vast majority of the land within the study area is undeveloped,
development pressures are mounting rapidly and many projects are presently
being considered. The preparation of a master drainage program is considered
an intregal part of the planning process for the North Palm Desert area.
� Topographically, the study area is typified by rolling desert terrain with
a flat ridge running from the northwest to the southeast and generally paralleling
Interstate 10. The ridge divides the study area into two distinctive drainage
basins. The area northerly of the ridge slopes steeply to the northeast to a
low point paralleling Interstate 10 and the Southern Pacific Railroad tracks. A
" larger basin, covering nearly two-thirds of the study area, drains to the south
� and southwest to the Whitewater River Stormwater Channel. The northerly
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basin has generally consistent slopes ranging from 32% to 5Z o and tending in
a northeasterly direction. Water collects along the southwesterly side of the
'�"' Southern Pacific railroad tracks then drains southeasterly parallel to the rail-
road.
The southerly basin is far less uniform. The ridge is broad with a
poor defined ridge-line. Local variations and sand dunes disrupt an other-
�r wise nearly level plateau. Drainage from the ridge tends in a southeasterly
di rection .
The west side of the riage is characterized by moderate to steep slopes
generally tending to the southwest but with localized "rivulets" which channel
� drainage southeasterly. Below the ridge slopes, the land flattens considerably
and drainage tends to flow in a southerly direction. This flatter area includes
a belt of sand dunes in which the contours and drainage patterns are virtually
indiscernable.
Presently, runoff in the study area is of little consequence due to the
""' sparsely developed nature of the area and the high porosity of the soils. As
development occurs, however, greater volumes of runoff can be anticipated and
the opportunities for inconvenience or property damage from flooding will increase.
1.3 - History of Drainage
Historically, two generally distinct flood control problems have existed
in the Coachella Valley. The first involves runoff from storms occuring in the
adjacent mountain ranges. Storm water is carried into the valley via the White-
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water River and its tributaries. Heavy rainfall in these mountainous areas com-
bined with spring snow melt has contributed to major floods in the past. (t)
This type of storm would potentially affect only the extreme northerly portion of
the study area and is not considered a matter of strictly local concern, but rather
one of regional nature.
The second iype of drainage problem is that resulting from storms occuring
primarily over the valley floor. Although such storms are relatively infrequent
and the runoff quantity small in comparison with those generated in the watersheds
of the adjacent mountain ranges, they are of primary importance in planning a local
(1) Master Drainage Plan for the City of Palm Desert. I.Harold Housley Consulting
Engineers/Willdan Associates. June, 1976, Page 5 and Page 39.
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drainage system. While annual rainfall is low in the Coachella Valley, storm
intensities tend to be relatively high. Such storms, though infrequent, can
�,. deposit considerable amounts of rainfall during short periods causing greater
accumulations of runoff than might otherwise be expected in an arid area.
Thunderstorm activity of this type was the cause of substantial damage in
Palm Desert in 1948 and again in 1951 .
1.4 - Conclusions and Recommendations
Storm flooding in the City of Palm Desert, as in other parts of the Coachella
Valley, is an infrequent but significant problem. In order to avoid some of the .
difficulties which exist in presently developed areas of the City, a coordinated
`� program for regional and local flood control facilities is required. The implemen-
tation of the recommendations contained in this report should provide the City
with an acceptable level of flood control protection. The estimated project
cost of the recommended system is approximately $14.6 million based on current
construction prices.
Various methods of funding drainage system improvements are available
to the City. Among these are assessment district proceedings and drainage fees
charged to developing properties.
�, It is recommended that the City adopt the comprehensive plan and drainage
set forth herein as the "Drainage Element" for the City's General Plan for the
project area and that it urge planning and construction of a regional drainage
facility paralleling Interstate Highway 10.
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CHAPTER2
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STUDY APPROACH
2.1 - Existinq Drainage Patterns and Facilities
As was indicated previously, the existing terrain divides the study
area into two natural drainage basins. For purposes of this study, these
areas have been identified as the "North Slope" and "Whitewater River"
basins. The general limits of the natural drainage basins are shown in Figure 1.
'r" Until recently, drainage patterns and runoff in the study area were of
little concern since the area was sparsely developed. The normally arid con-
ditions and the high porosity of the soils combined with the very low potential
for property damage, made consideration of drainage facilities unnecessary.
The advent of numerous private development programs within the study area
�+' has made planning and construction of an adequate drainage system imperative.
The Coachella Valley County Water District has regional responsibility
for flood control in the central and southern portions of the Coachella Valley.
The District maintains several major facilities which provide flood protection
to the City of Palm Desert and other communities within the District's bound-
aries. One of these, the Whitewater River Stormwater Channel, traverses the
study area along its southern perimeter. The Whitewater River Stormwater
Channel is the major watercourse in the upper Coachella Valley and provides
the primary outlet for storm flow from virtually all of the City's presently
developed properties.
2.2 - Flood Frequency
The level of protection offered by a drainage system is commonly defined,
+� on the basis of statistical probability, as the number of years between storms
of comparable intensity. Storm intensities are usually identified as relating to
a particular "flood frequency"; typically, 10, 25, 50 or 100 year events. The use
of this "return year" terminology is common since rainfall intensity and runoff
quantities are generally recorded on an annual basis. A particular flood can be
,�„ identified in terms of runoff resulting from a storm which would occur, statisti-
cally, an average of once in a certain number of calendar years. For example,
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MAIOR DRAINAGE AREAS
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FIGURE 1
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a 25-year frequency storm would be one that, over a very lengthy period,
would occur on the average of once every 25 years. Similarily, a 100-year
++►� storm would be a storm which, on the average, would occur once in every
10U years.
Drainage facilities are usually designed to provide protection from storms
of specified frequency. Storms of lesser frequency would only partially fill the
,�, drainage facilities, and storms of greater frequency would generate runoff quan-
tities beyond the capacity of the facility.
While many communities throughout the United States have adopted flood
protection criteria to satisfy other frequency storms, many agencies now require
flood protection for a storm with a recurrence interval of 100 years. Generally
speaking, as the area tributary to a drainage facility increases with size,
the storm frequency takes on greater significance. For example, when hydro-
logic studies for floods of 10-year and 50-year return frequencies were con-
ducted on two drainage basins of similar characteristics but with areas of
100 acres and 1, 000 acres, respectively, the computations demonstrated
that the runoff rates for the 50-year storm were in both cases nearly double
those for the 10-year flood. However, the increase in the flow rate for the
larger area was nearly 10 times that of the smaller basin. The significance
of this difference in magnitude indicates that facilities serving larger tributary
areas may need to be sized to carry storm flows from a higher frequency storm
since the ability of surface features to accommodate the excess flow is usually
limited.
The analyses conducted as a part of this investigation, were based on storm
intensities of 25-year and 100-year frequency.
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2.3� Methodolo�
The approach used to define the local drainage system for the study area
has been developed using hydrologic criteria of the Riverside County Flood
w+ Control and Water Conservation District, The primary data source was the
District's Hydrology Manual.
The initial aspects of the investigations involved the establishment of the
study area limits and discussions with representatives of the City of Palm
,� Desert and adjoining communities. The discussions centered on the responsi-
bilities of the various entities with respect to the control of surface drainage
along common political boundaries. It was evident from these preliminary
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discussions that, while other agencies were interested in drainage planning
for those portions of their jurisdictions lying to the north of the Whitewater
� River, their programs were not yet as advanced as Palm Desert's.
The Coachella Valley County Water District indicated that a number of
area studies had been conducted along the Whitewater River Stormwater
Channel and a few other selected locations such as the Thousand Palms area
� north of Interstate 10. The District had not however, conducted any extensive
""' planning with respect to local drainage within the study area. The staff of
the City of Rancho Mirage, during informal discussions, expressed the desire
for development of local drainage plans but indicated that limitations on local
funding have prevented authorization of the work.
The proposed Palm Desert program was reviewed with the staff of the City of
Rancho Mirage and conceptual approval was given to the establishment of Monterey
Avenue and its northerly extension as the common boundary of drainage responsibility
within the area tributary to the Whitewater River, This determination is significant
in that there are several localized areas lying westerly of Monterey Rvenue which
under existing conditions could contribute surface water runoff to the project study
area. These areas are distinguished by the unusual characteristic of having the
general land form slope to the southwest while the localized channelization of storm
flow (i,e., the rivulets) directs water to the southeast. This "rivuleting" condition
is a localized one which will, in all likelihood, be eliminated with the development
of properties. It was mutually determined that such areas could be excluded from
the area tributary to the Palm Desert system.
The circumstances in the "North Slope area" are considerably different.
Since all the properties in the Rancho Mirage sphere of influence located north-
�, erly of the ridge line have no other outlet than to drain easterly along the northern
.r boundary of the study area, their contribution of storm flow must be considered
in the planning and design of local and regional facilities.
The drainage boundaries agreed upon with staff of the City of Rancho Mirage
and the limits of major tributary areas were shown in Figure 1.
Having established a conceptual agreement with the City of Rancho Mirage
with respect to the common limits of drainage responsibility, the following analyses
were made:
(1) All drainage areas within study area were defined in detail.
(2) Existing drainage facilities were classified and documented
as to size and location.
(3) A field reconnaissance survey was conducted.
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(4) Data on proposed land use, drainage patterns, topo-
graphy, rainfall intensity, etc, were compiled.
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(5) Estimated runoff quantities were determined using the pro-
cedures of the Riverside County Flood Control and Water
Conservation District for each local drainage basin and for
storm intensities of 25-year and 700-year frequency.
(6) Additionally available data such as that on existing topography,
drainage facilities, and design criteria were included in the
analyses. Studies were conducted to determine the facilities
necessary to satisfy the flood control requirements for the
proposed storm flow frequency. 5torm flows were considered
to be carried by existing street section to the extent that
sufficient capacity was available to carry flood flow without
damage to adjacent properties.
(7) Various alternatives were developed and compared to determine
the most appropriate system for the study area.
(8) Several alternative designs were considered to establish
the lowest cost alternative which would adequately provide
for the level of protection dictated by the assigned storm fre-
quency. The alternative drainage systems included consi-
deration of retarding basins, open and closed conduits, alter-
native system alignments, and proposals for possible regional
drainage facilities.
(9) Subalternatives and refinements were applied to the lowest
cost alternatives in an attempt to optimize the facilities plan.
The proposed facilities were then prioritized on the basis of their impor-
tance, the overall system function, their cost effectiveness, the relative loca-
tion with respect to existing regional facilities and current or proposed develop-
ments. The resulting plan is presented as the recommended master plan of
drainage for the North Palm Desert area.
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CHAPTER3
TECHNICAL STUDY
3.1 - Hydrologic Studies
Hydrologic studies conducted in connection with the master plan investi-
gation were conducted utilizing the "rational method" in combination with the
"synthetic unit hydrograph method" as adopted by the Riverside County Flood
Control and Water Conservation District. The District's method and criteria
have been developed from, and are generally consistent with, data generated
by the California State Resources Agency. The formula and procedures utilized
are documented in the RCFC & WCD Hydrology Manual dated April, 1978.
The rational method computes runoff as a function of area, rainfall in-
tensity, and a coefficient of runoff. The basic formula used in the rational
method is as follows:
Q = CIA Where:
� Q= Runoff (in cubic feet per second)
C = Coefficient of runoff
I= Rainfall intensity (in inches per hour)
A = Land area (in acres)
The rational method was used as the primary analysis technique because of its
simplicity and because it is the method most likely to be utilized in the design
of facilities to serve development projects within the study area. The method
has however, certain inherent limitations. It is most appropriately used on
relatively small areas, usually of 500 acres or less. While several of the drain
age areas within the study limits are within these limitations, others are not.
Hydrology computations using the synthetic unit hydrograph method were
developed for the larger drainage areas and used for comparison with the cal-
culations made using the rational procedure. Where warranted, appropriate
adjustments in projected flows and facility sizing were made.
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It should be noted that since the rational method generally tends to
result in higher flow rates, it provides an additional factor of safety. Because
�' of the general nature of the master drainage plan, the use of the higher flow
rates is not particularly undesirable. More precise hydrology computations
will, of course, be an appropriate prerequisite to the design of system elements.
3.2 - Coefficient of Runoff
The runoff coefficient is a factor which represents the ratio of the rate of
stormwater runoff to the rate at which rainfall occurs. The runoff coefficient
is a function of a number of factors, the most significant of which are the
type of development and the infiltration capacity of the soil. The procedure
utilized in the RCFC � WCD Manual relates the runoff coefficient to the soil group,
the type of surface cover, and the rainfall intensity. The District has established
a series of curves which represent the characteristics of the various regions
within their jurisdiction. The runoff coefficient curves used in this investiga-
tion are those for Soil Group A, Cover Type-Urban Landscaping AMC-II (Run-
off Index #32) as indicated on Plate D-5. 1 of the District's Hydrology Manual.
3.3 - Rainfall Intensi
Intensity is expressed in inches of rainfall per hour and is developed by
statistical methods from recorded rainfall data.
There are not rainfall recording stations within the City of Palm Desert
that have the type of equipment necessary to establish rainfall intensity deter-
�, minations; therefore, the rainfall intvnsity data utilized in this investigation
were established on hydrology data developed by the Resources Agency of the
State of California and incorporated into the RCFC & WCD Hydrology Manual .
Rainfall intensity rates are the results of many factors, the most signi-
»� ficant of which is the duration of the storm and the statistical average recur-
''�` rence interval (10-year, 25-year, 100-year, etc.) .
The relationship between rainfall intensity and the duration of the storm
is a complex, inverse function that can be characteriz.ed by the general statement
that rainfall intensities for a given recurrence interval can be very high for
short periods of time, regressi�g to lower average values as the time period is
increased.
10
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�
Intensity-duration curves were constructed for 25-year and 100-year
frequency storms using the procedures established in the RCFC & WCD Hydro-
+� logy Manual, Data for the construction of the intensity-duration curves were
obtain from the isohyetal curves on Plates D-4.3 and D-4.4 of the Hydrology
Manual, Additional data necessary to develop the intensity-duration curves
can be found on plates D-4.5 and D-4.6.
3.4 - Planned Use
A critical element in the development of the master drainage plan was
the land use within the study area. The area is presently sparsely developed
but numerous projects now under construction or in the planning stage will
� drastically alter much of the land use within the next few years.
The master plan of drainage for the North Palm Desert area has been dev-
eloped using the land use criteria indicated in the General Plan Amendment
, currently being considered by the City of Palm Desert,
�
Land use is a very significant consideration with respect to drainage
planning. The intensity of development and the amount of surface covered with
impervious materials can significantly affect the quantity of storm runoff.
The following table illustrates typical coverages for various classifications
,,,, of development:
Coverage of
Development Impervious material
Commercia l
900
High Density Residential 800
Medium Density Residential 50$
Low Density Residential
40 0
Combination Golf Course
and Condominium 40 - 50$
�
11
+�.
yr
3.5 - Limitation of Stormflow from Developments
ar
In the course of this planning investigation, consideration was given to
a number of various conditions which could be applied to development projects
as a means of reducing the storm runoff. The proposed conditions w�uld limit
the amount of water that various types of development could discharge to
public streets or drainage facilities.
From the analysis of these proposals, it was evident that certain types of
development would lend themselves to some kind of restriction on the amount of
drainage that could be released. It was determined that low density residential
projects which incorporate large open space areas, such as greenbelts or
golf courses, could be designed to accommodate such restrictions with relative
ease. Several projects currently under construction or in a planning stage
have incorporated such provisions in their design and conversations with other
developers indicate that such requirements would not be unduly difficult to
incorporate in similar projects.
�r
The basic approach to runoff limitation is to provide retention capability
as an intregal part of the open space or recreation areas of each project.
This capability typically involves the creation of "sump areas" where limited
amounts of storm water can be ponded. The accumulated water could be allowed
to evaporate, percolate into the underground or be released to the drainage system
�"' at some point in time after peak discharge rates occur. This retarding of storm
flow wbuld have the effect of reducing the overall peak flow rate in the drainage
system.
In studying the various proposals for drainage reduction conditions, it
+rr became evident that such conditions could not be universally applied within
the study area _ There are numerous properties for which such a condition
cannot be reasonably applied. These include:
� (1) Existing developments.
(2} Developments occuring under the jurisdiction and
control of the County of Riverside.
(3) Parcels of limited size or having physica) features
'�d'' that would make the inclusion of retarding basin
i mpracti ca l .
12
W.
vr�
(4) Properties with land uses which do not incorporate
�'' sufficient open space area within which to develop
retarding basins.
A number of formulae were considered for implementation of a policy
�, requiring retardation of peak storm flows as a condition of development. While
the specifics of the proposals varied somewhat, the basic premise was consis-
tent, Based on the study of the alternative proposals, the following recommended
retardation criterion is suggested as appropriate for developments within the
study area.
Developments of 10 gross acres or more shall provide sufficient
on-site stormwater retention and/or retardation so as to limit
peak runoff during a storm having 25-year intensity to a rate
no greater than that which would have otherwise occured under
�' undeveloped conditions.
This requirement would make it incumbent upon developers to provide
sufficient temporary storage within the limits of their project to hold approxi-
,�, mately 800 of the runoff that would occur during the 25-year storm. The
ponded water would be dissipated through evaporation, percolation, or
through release to the drainage system after the passing of the storm.
5uch a requirement would greatly reduce the anticipated systemwide
" runoff from a 25-year storm; it would also redu�e the flow rate that would be
ar
generated by storms of greater intensity. For example, if such a condition
is imposed, the City's drainage systems would receive peak runoff rates from
a 100-year storm that would approximate those that would result from a
25-year storm on an equivalently developed property not having retarding
basins.
�
Review of this concept with engineers representing several of the major
developers in the area has indicated general agreement with the feasibility
of such a program. Indications are that the cost of providing this retarding
capacity would be nominal in most cases and could result in significant savings
�
�
13
�
r.
to the City and to the general public through reduction in the cost of drainage
fees assessed to the development projects.
3.6 - Hydraulic Studies
Facilities for the conveyance of stormwater were sized to accommodate
�" storms of 25-year and 100-year return frequency using the flow limitation criteria
described in the previous section. Drainage conduits have been provided in those
locations where anticipated storm flows would exceed the carrying capacity of
surface streets. The full carrying capacity of the streets was also utilized to
help reduce the size of drainage conduits. Underground. storm drains have been
�,,,, generally sized to flow without pressure. However, in some instances, particu-
larly where related facilities such as open channels or retarding basins require
higher hydraulic gradients, pressure flow was permitted provided that the
energy gradient did not rise above the ground surface. For the most part,
subsurface drains were assumed to be established on a slope parallel to the
ground surface along their route. Pipeline sizes were selected to the nearest
'� 3-inch diameter; in some instances, however, box culvert alternatives were
utilized where circular conduit sizes became unrealistic in terms of potential
availability and/or feasibility of construction.
Open channel designs were based on the most effective section (considering
+� construction conditions and maintenance costs) and assuming uniform flow with
the water surface generally parallel to the longitudial gradient of the channel.
Depths of the channe) were established using two feet of freeboard between the
estimated water surface and the top of the channel wall .
Hydraulic design calculations developed in the study are based on Manning's
formula. The formula and its t?rms are described as follows:
V = �.48G �v3 Svz
n
�
�"i
V= Velocity of Uniform Flow (feet per second)
n = Roughness Coefficient
R = Hydraulic Radius (feet)
s= Slope of Energy Gradient (feet per foot)
14
.r
,�
The following values of n were used for various elements of the conveyance
system:
"� Reinforced Goncrete Pipe (RCP) n= 0.013
Reinforced Concrete Box n= 0.015
Open Concrete Channels n= 0.015
�" In all cases, hydraulic analyses assumed that the streets would be free
and clear of major obstructions and that the drainage system would be ade-
quately maintained so that blockage would not occur.
,,, 3.7 - Retarding Basins
Among the alternatives considered in the development of the master drain-
age plan were the incorporation of retarding basins. The major benefit of such
basins is in achieving a reduction in the sizing of downstream conveyance facilities.
In considering retarding basins, it was assumed that they were to:
(1) Be utilized as multi-purpose facilities, perhaps as
parks, playgrounds, or for similar recreational pur-
poses. (Development costs for secondary uses were,
however, not included in the cost analyses.)
(2) Be limited in dimension to avoid designation under State
criteria as a major impoundment or dam structure.
(3) Be placed only in areas of generally compatible land
use as defined in the City's proposed Land Use Element.
Six potential sites for retarding basins were investigated using the general
criteria listed above. Of these, only one, in the proposed Sand Dunes Park, was
considered feasible. Various analyses were conducted on the Sand Dunes Park
site to determine the most desirable approach to a retarding basin. Among the
plans considered were two separate basins serving the Portola and Rebecca
systems. A single, combined basin serving both the Portola and Rebecca
systems was found the most cost effective of the retarding basin alternatives.
The suggested retarding basin would have a storage volume of approxi-
�'` mately 135 acre feet with a surface area of approximately 30 acres. Various
preliminary studies indicate that the basin would have a elongated shape with
15
��
�
its greater dimension extending in a northwest/southeast direction. The basin
could be irregularly contoured so as to provide a"natural" and aesthetically
acceptable appearance. The basin would be compatible with the proposed open
`7i� space use of the park. The soil conditions on the site are particularly
suitable in that they will permit a high degree of infiltration, further reducing
the outflow from the basin.
The use of a portion of the Sand Dunes Park site as the retarding basin
+�' would have great economic advantage in that it would reduce the total cost of
facility construction by nearly $3.3 million. This saving does not include, how-
ever, land acquisition cost or the cost of any park related construction.
Although it is believed that the retarding basin concept is basically com-
,r,, patible with the conceptual planning for Sand Dunes Park, there are some inherent
disadvantages to such basins. These include:
(1) Limitation on Future use of the retarding basin site. -
If upstream and downstream elements of the drainage
system are constructed on the basis of a plan con-
taining a retarding basin in Sand Dunes Park, future
development of the park area would be constrained
to the extent that the basin area would be subject to
inundation .
(2) Hazard a�d Liability Aspects - When functioning as a
retarding basin, the facility would present a potentially
hazardous condition. This is particularly true if security
fencing is considered aesthetically unacceptable.
16
�
�
CHAPTER 4
PROPOSED MASTER PLAN SYSTEM
As a result of the investigation summarized in this report, a compre-
�, hensive master plan of local drainage for North Palm Desert area was developed.
The basic plan provides for flood protection for a storm of return frequency of
100-years utilizing the drainage limitation criteria discussed in Chapter 3.
In addition to subsurface drainage facilities, the plan proposes certain surface
improvements including the construction of retarding basins in Sand Dunes Park,
southerly of the proposed extension of Hovely Lane and easterly of Portola Avenue
'�' and adjacent to Interstate 10 easterly of Cook Street. The plan also suggests the
construction of approximately 4, 800 feet of trapezoidal channel along the north side
of Frank Sinatra Drive. The various conveyance facilities utilized in the master
plan are illustrated in Figure 2.
4.1 - Identification of System Elements
In order to easily identify the various system elements, reference codes
have been used to identify each reach of conduit. The reference codes consist
,�„ of a letter prefix followed by a number. The prefix code indicates the major system
branch. For example, the Rebecca Branch is identified by the code letter R, while
the Frank Sinatra Branch is identified by the code letter FS. The numerical
portion of the reference code generally indicates the relative location of the
reach. Numbers have generally been assigned in increasing numerical sequence
° from the downstream end of each branch. Thus, a pipe reach with a small number
"" can be expected to be located near the downstream end of the branch while one
with a relatively large number is usually located near the upstream end.
Table 4-1 lists the reference codes for the various system elements.
TAB LE 4- t
FACILITY IDENTIFICATION CODES
Prefix
C
DS
FS
MN
MS
PH
PN
R
B ranch
Cook
Del Safari
Frank Sinatra
Monterey (North)
Monterey (South)
Portola JHovely
Portola (North)
Rebecca
, <
17
..
�
.
�� CONVEYANCE
SYMBOL USED
ON
MASTER PLAN
TYPICAL SECTION
�- -STREET SURFACE
T
REINFORCED
CONCRETE PIPE
72��
�
INDICATES 72 RGP----�
CONCRE7 E LINED
TRAPEZOIDAL
CHAN N EL
36 K 6�
�%
�
INDICATES TRAPEZOIDAL �
CHANNEL W=36�/h-6�--�
� ,
�
N / �/�/ R / W
V
�S� W 'IO�
.._. _____. _._—_ay�—�
—. 1
� �
� b� x
.. '1 L _ .. J'I Fl �a�. ,.
2 2 -r—�
REINFORCED
CONCRETE BOX o'x� e'xe'
� J
� ir�oic,o,TEs ooua�E eox
wsa'� h=6'—
INUICATES SINGLE BOX
W: E3'/ he 6' —. ---- — --__ __ ----
�r _ _
m.9%-... -�-- iA
CONVEYANCE FACILITIES
� FIGURE 2
..
�
4,2 - Drainage Area Designations
Drainage areas have been identified with the drainage system to
which they are tributary. The same one or two letter reference code
used to identify the various system elements has been used to identify
the tributary basins. For example, drainage area PH includes all the areas
tributary to the Portola/Hovely drainage system and drainage area C in-
cludes those lands served by the Cook system. The various basins are
indicated on Figure 3.
4.3 - Description of the Proposed Drainage System
'" The proposed system consists of a series of semi-independent drain-
age networks which discharge either to the Whitewater River Stormwater
Channel or to a suggested regional drainage facility which would parallel
Interstate Highway 10. The recommended plan divides the study area into
�, two major basins. The North Slope Basin which drains toward Interstate
�► 10 and the Whitewater Basin which drains southerly to the Whitewater River
Stormwater Chanr�el. The proposed system would establish the boundary
between the two major basins along Frank Sinatra Drive from Monterey Avenue
easterly to Cook Street, then southerly along Cook Street to County Club
�,
Drive, and then easterly along Country Club Drive to the east boundary of the
,,, study a rea ,
The North Slope basin is served by four branch lines. These are
the Monterey (North) Branch, the Portola (North) Branch, the Frank Sinatra
Branch and the Del Safari Branch.
Each of these branches serves a distinct local service area. The Monterey
(North) Branch collects water from an area generally limited to southwest one-
quarter of Section 29. The Portola (North) Branch serves the portion of Section
32 northerly of the ridgeline as well as a portion of Section 29. The Del Safari
Branch will collect water from the westerly one-half of Section 3.
The Frank Sinatra Branch is the most significant facility in the North
Basin. It is both the largest facility in the basin and the only one which will
collect water from areas lying south of the ridgeline. The proposed alignment
of the Frank Sinatra Branch will divert drainage from about 500 acres from its
natural flow pattern, (i.e., to the Whitewater River) . Drainage generated in
a large part of Section 32 and a portion of Section 33, insteac! of flowing south
to the Whitewater River, wi II be carried easterly to Cook Street and then north
to a suggested regional drainage facility. Because of this diversion of storm flow
. 19
�
�
�\ \
�
i
9�TF �
qS
Tq
rF
4°�F, �
PN
- - - - - �'� -
i
i �
I
-� r,�--,--���-' - _ - -�- - - - -
� Area subject to inundation
; � ��;_ �«
Area of possible inundation
� , . ,�;
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�
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�
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>
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:�,
� _�____
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SINATRA
�
N �_ 1
C7
__ _ __ _ _ �
�
� - -� - �_
, ; �- - fi-
I
�
� � � � �
t----� ' � '
— - - - ,' _ i_ _, t.
I I - --_ - � —
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' � � � I
i � I
PH I �� I ,
TRY
CLUB I DR I
I I I
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i i
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48 , Ir � I
13 do�. II � I
��7
��% I �
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-� �_ _ I _
�-
8 00�� Con dof.
, i�
1/�� �
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i
` 1120 Mi�d
� ����
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and the possible increase in flow that could result, consideration was given to
inclusion of a retarding basin on the Frank Sinatra Branch near the north-
' easterly corner of the study area. However, detailed hydrologic analysis
� indicated that the additional 500 acres would have no appreciable effect on
peak storm flows in the regional facility suggested to parallel Interstate 10.
Under project storm conditions peak discharge from the 500 acre area would
reach the suggested regional facility more than three hours before peak dis-
� charges would be antieipated. Consequently, the retardation of storm flow
�+' from the Frank Sinatra tributary area would serve no useful purpose.
The Whitewater Basin area is served by three branch systems. Under
Alternative "A" (the recommended alternative) stortn flow from the Portola/
Hovely and Rebecca Branches is channeled to a retarding basin located in the
proposed 5and Dunes Park. Outflow from the retarding basin reaches the White-
water River through an extension of the Rebecca system. Under Alternative "B"
the Portola/Hovely system drains easterly along Hovely Lane then southerly
along Portola Avenue to the Whitewater River 5tormwater Channel. The Rebecca
system drains southerly near the mid-section lines of Sections 4, 9, and 16, and
discharges to the Whitewater River at a point near the intersection of Rebecca
Road and Gary Avenue. The alignment and sizing of Cook Branch is the same
under both alternatives.
The Portola/Hovely system serves all of Section 5 and the northerly one-
� half of Section 8. The Rebecca system drains Sections 4, 9, and the majority of
+� the portion of Section 16 located northerly of the Whitewater River Stormwater
Channel. The tributary limits of the Cook Branch generally include the westerly
one-half of Section 10 and 15 as well as portions of Sections 9 and 16.
4.4 - Alternative Systems
The recommended facilities plan (Alternative "A") is shown in Figure 4. The
recommended alternative includes the retarding basin located at the site of Sand
Dunes Park. An alternative plan (Alternative "B") has also been presented (see
'�' Figure 5) . This alternative does not include the retarding basin and has separate
� outlets for the Portola/Hovely and Rebecca systems.
Subalternatives were also considered for that portion of Portola/Hovely
system along Hovely Lane. Conduit sizes in this area are very large due, in part,
� to the nearly level profile that exists along Hovely Lane. A second factor in the
� large size of the conduits is the extent and nature of the tributary area.
The Portola/Hovely system serves more than 1,200 acres in an area between
Portola and Monterey Avenues southerly of Frank Sinatra Drive. More than two-
thirds of this area is either presently developed or has development pending
•
21
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�� ' ' �' � ���'�� � Area of possible inundation
- -�- - --�
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which will be completed under the jurisdiction of the County of Riverside. As
a result, the runoff limitation criteria suggested in Chapter 3 cannot be imposed.
Additionally, a number of parcels fronting on Country Club Drive and Hovely
Lane are held in ownerships of less than 10 acres. These properties appear to
be too small to effectively implement the runoff limitation criteria. As a conse-
quence of the inability to restrict the runoff from these properties, the computed
runoff quantities for a given storm are considerably higher than what otherwise
would have been the case.
Another important factor is that, while the area tributary to the Portola/
Hovely system is in excess of 1,200 acres, only about 570 acres will be potentially
subject to offsite drainage fees. In effect, this means that only 470 of the Portola/
Hovely system can be financed by the assessment of drainage fees to developing
properties .
Review of this particular situation with City staff resulted in a development
vf a pair of additional subalternatives. These have been designated Alternatives
"A-1" and "B-1". The subalternatives are similar in concept and in alignment to
Alternatives "A" and "B", but have been sized to provide for storm with a return
frequency of only 25 years. These subalternatives, of course, are less costly
than the basic alternatives but also provide a lower level of protection for the
properties in the Portola/Hovely tributary area.
4.5 - Priority Schedule
The suggested priorities for the various drainage conduits in the recommended
plan in Table 4-Z. Priorities have been established on the basis of a scale of 1 to 5
��, with 1 representing the highest priority. It should be noted that these priorities
�► are based on currently anticipated development schedules and may require revi-
sion from time to time as further development occurs within the study area.
4.6 - Regional Drainage Facilities
The successful implementation of the master drainage program will require
cooperative efforts with a number of other public agencies. The availability of
a regional drainage facility paralleling the Southern Pacific Railroad tracks and
Interstate Highway 10 is of prime irnportance to drainage planning in the North Slope
area.
24
�r
�
TABLE 4-2
�
�rr SUGGESTED PRIORITY SCHEDULE
FOR RECOMMENDED FACILITIES PLAN
Drainage
Area
Cook
Del Safari
Frank Sinatra
�r
�
�
Monterey (North)
Portola/Hovely
�
Facility
Code
C1
C2
C3
C4
C5
D51
FS]
FS2
FS3
FS4
FS5
F56
FS7
MN1
MN2
MN3
PH1
PH2
PH3
PH4
PH5
PH6
PH7
PHS
PH9
PH 10
25
Priority
Index
3
3
3
4
4
4
4
4
4
4
4
5
5
5
5
5
1
1
1
1
2
2
2
2
2
2
�
�
TABLE 4-2, continued
Drainage
Area
Portola (North)
Rebecca
Retarding Basins
Faci I ity
Code
PN1
PN2
PN3
PN4
PN5
PN6
R7
R2
R3
R4
R5
R6
R7
R8
R9
R10
RB1
R62
26
Priority
Index
5
5
5
5
5
5
1
1
2
2
2
2
2
3
3
3
1
4
.w
The topography and constraints imposed by the railroad and freeway
virtually dictate a major drainage facility along this corridor. Such a facility could,
+•� and most likely would, serve parts of upstream agencies such as Palm Springs
and Rancho Mirage as well as downstream entities. It is suggested that, as a
part of its development planning for the study area, the City should encourage
regional drainage planning by the Coachella Valley County Water District.
� It has been assumed in the preparation of this master drainage plan that a
regional outlet would be provided by the CVCWD along the northerly boundary
of the study area. Since such a facility would benefit a number of agencies, its
cost has not been included in this facilities plan.
4.7 - Areas Susceptible to Inundation
Portions of the North Slope Basin adjacent to Interstate 10 could be sub-
ject to inundation under certain conditions. The area consists of a strip of
land varying from 300 to 1, 100 feet in width lying immediately adjacent to the
Southern Pacific Railroad tracks. This band of land would be in the path of
storm runoff from a nine square mile area lying to the northwest.
Under conditions of full upstream develo�ment (as envisioned by existing
general plans) the 100-year, 3-hour discharge in the vicinity of Cook Sireet
� would be in excess of 2,100 cfs. Unless a regi�nal conveyence facility (such
as the one discussed in Section 4.6) is constructed storm flows of this magni-
tude would cover low lying areas adjacent to the railroad.
The areas of potential inundation have been indicated on Figures 3, 4,
° and 5. The limits of these areas have been �stablished on the basis of existing
'� contours and would change wsth significant grading. Construction of a suitable
sized regional facility would eliminate or significantly reduce the area potentially
vulnerable to flooding.
27
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�
CHAPTER5
EST{MATED COST OF MASTER PLAN IMPL�MENTATION
This chapter presents a summary of the estimated cost for implementing
- the North Palm Desert master drainage plan. Additionally, cost comparisons
� have been made for alternatives to the recommended plan including 5ubalter-
natives "A-1" and "B-1".
5.1 - Basis of Estimates
The estimated costs listed in the following tables are based on a current
(March, 1979) construction cost for projects of similar nature and magnitude.
It has been assumed that this master plan would be implemented on an incremental
basis as development occurs in various portions of the study area and as sufficient
funds are collected from off-site drainage fees.
Since it is likely that construction of many of the recommended drainage
facilities will be deferred, the total cost of the master plan implementation will be
subject to future construction cost increases . Whi le no attempt has been made
to project future construction prices, a review of the historic trends in construc-
tion costs cloes provide some insight. Figure 6 illustrates the recent history
of two construction cost indices. The first is the construction cost index for the
Los Angeles area published quarterly by Engineering News Record Magazine (ENR) .
This index is established using as its base construction costs prevalent in the
year 1913. ENRs latest construction cost index (March, 1979) was 3, 421 . This
compares with an index of 1,029 in June of 1966.
The second index illustrated in Figure 6 is the cost index for concrete
pipelines compiled by the U.S. Bureau of Reclamation. This index, published
quarterly, is based on 1967 value of 1.0. Its level, as of January 1979 was 2.26.
The Bureau's level for concrete pipeline construction has shown a 20 percent in-
crease over the last 3 years .
On the basis of recent trends in the two indices, construction costs could
be expected to double within 8 to 10 years. Whether or not these inflationary
trends will continue, of course, is a matter beyond the control of the City. It is
recommended, however, that the funding programs established for implementation
of the master plan of drainage for the North Palm Desert area make provision for
the increased costs of deferred construction.
28
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��
3500
t.5
:r+
3000
K
W 250
0
z
F" o
0 0 2000
V�
Z ��
M
� �
F' � 1500
t� w
� �
�' Q
�m
N
Z
p 1000
V
�
Z
W
50C
N
W
Z
Z �
O W
z.o F a
aa
� W
J ~ �
W .=
V CC tl
� V �
Z Q,
1.5 � O �
O v �,:,
Cn
Q O m
W �
�
�x
m W
0
1.0 M Z
�-
H
N
O
V
�
�
I
YEAR
CONSTRUCTION COST 1NDlCES
FIGURE 6
�
�:�
5.2 - Estimated Project Costs
Table 5-1 summarizes the total estimated project cost for the proposed
master plan system. These costs include construction, engineering, adminis-
trative, legal, financing costs as well as a factor for construction contingencies.
Land and right-of-way costs include $900,000 for purchase of a 30 acre site for
a major retardation facility to be included in the proposed Sand Dunes Park. The
total project cost of the recommended master plan is estimated to be $14,300,000.
TABLE 5-1
ESTI MATED PROJ ECT COST OF
RECOMMENDED DRAINAGE PLAN
Construction Cost
Contingencies @ + 10 0
�
Land and Right-of-Way Acquisition
Technical, Legal and
Administrative Costs
$10,715,000
1,070,000
$11,785,000
1,065,000
2,350,000
$15,200,000
TOTAL PROJ ECT COST
The project costs of the various system elements are listed by drainage
basin in Table 5-2.
TABLE 5-2
ESTIMATED BASIN COSTS
FOR RECOMMENDED DRAINAGE PLAN
Drainaqe Area
Cook
Del Safari
- Frank Sinatra
''i" Monterey (North)
Portola/Hovely
Portola (North)
Rebecca
TOTAL PROJECT COST
Project Cost
$ 2,300,000
600,000
2,250,000
420,000
4,970,000
910,000
3,750,000
$15,200,000
30
�
�
5.3 - Proiect Cost of Alternative Systems
� The master plan considered several alternatives to the recommended
facilities plan. These were previously discussed in Chapter 4. The following
are our estimated costs for these various alternatives.
Alternative "A" - Recommended system with capacity for
"r` 100-year frequency storm utilizing a retarding basin in
Sand Dunes Park.
Estimated Cost: $15, 200, 000
Alternative "A-1" - Similar to Alternative "A" except that
� design capacity for the Portola/Novely system is based on a
25-year frequency storm.
Estimated Cost: $14, 130, 000
Alternative "B" - Similar to the recommended alternative except
� that no retarding basin has been utilized in the Whitewater Basin
necessitating a separate outlet for the Portola/Hovely Branch.
Estimated Cost: $18, 510, 000
Alternative "B-1" - Similar to Alternative "B" except that a
- 25-year frequency storm has been used as a basis for design
`"�' of the Portola/Hovely system.
Estimated Cost: $15, 660, 0�0
�
�
31
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�
CHAPTER6
FUNDING METHODS
For the master plan of drainage to be implemented it is necessary that some
,y„ mechanism be developed for project funding. The following discussion describes
several possible financing methods. For the most part, these are commonly
known and relatively simple techniques and are therefore, discussed only
briefly .
It is evident that a program of offsite drainage fees (or construction of
�" facilities by developers) could play a major part in implementing the master
plan of drainage. It will be necessary however, particularly with respect to those
facilities in the Whitewater Basin, to develop some additional source of financing.
6.1 - General Fund
General fund monies can be legally used for the construction of drainage
facilities to serve the community. However, general fund monies have almost
always been over-subscribed and since the advent of Propositivn 13 the likelihood
of general fund monies being used for construction of drainage facilities is extremely
remote .
6.2 - Drainage Fees
Under the provisions of the government code of the State of California, a
local governmental agency may adopt a program for the collection of drainage fees.
The Subdivision Map Act inables the City to enact a drainage fee program after
certain prerequisites have been satisfied. The requirements for the drainage fee
program include:
(1) Adoption of a master drainage plan program for each local
drainage area.
(2) Certification of the master drainage plan by the legislative
r,,, body of the County and/or special district having a County-
wide and/or districtwide drainage plan.
32
�
�
(3) Adoption of a fee structure based on the cost of the
required facilities for each drainage area and equit-
ably proportioned to all affected properties.
(4] Establishment of "local drainage facilities fun�ls".
Following adoption of appropriate local ordinances, drainage fees can be
collected from developers as a condition of approval of final subdivision maps.
°"` Funds are then deposited in the appropriate "local drainage facilities fund". They
may then be expended for engineering, administrative, and construction costs of
drainage facilities to be constructed within a particular drainage area. The
City may elect to waive the drainage fees provided that the developer of the
adjacent properties constructs a portion of the master plan system. The waiver
� of fees can be on a whole or partial basis depending on the value of the facilities
being constructed by the developer. Table 6-1 lists the area drainage costs
associated with the recommended plan.
TABLE 6-1
DRAINAGE COSTS
AS50CIATED W1TH THE
RECOMMENDED FACILITIES PLAN
0
Drainage
Area
Area
(acres)
Estimated Cost
of F�cilities
Drainage
Costs
(Per Acre)
Cook
'� Del Safari
Frank Sinatra
Monterey (North)
Portola/Hovely
Portola (North)
�' Rebecca
TOTA LS
*Overall Average
580
320
860
180
1, 220
280
1, 040
4,480
$ 2,300,000
600,000
2,250,000
420, 000
4,970,000
910,000
3,750,000
$15,200,000
$3, 960
1, 875
2,615
2,335
4, 075
3,250
3, 605
3,390*
33
�
�":
Since it would be impractical to establish and administer a system of
drainage fee collection based on seven fee structures and a system of rela-
tively complex drainage boundaries, the City may wish to establish the drain-
age districts on a broader base than that indicated in Table 6-1. Two possible
consolidations suggest themselves. One would be to consider the entire study
area as a single drainage district. The other would be to divide the study
area into two districts with a boundary running from the westerly City limit
along Frank 5inatra Drive, southerly along Cook Street and then easterly on
Country Club Drive.
The drainage fee for a single basin would be approximately $3,400 per
acre. For the two districts the fees would be $2, S00 for the northerly one and
$3, 700 for the southerly one.
The drainage fee program for the North Palm Desert area would be an
effective way in which to implement much of the master drainage plan. There are
areas, however, such as in the Portola/Hovely tributary basin where drainage
fees would offset only a part of the expense associated with the drainage program.
In these areas some additional source of revenue will be necessary to completely
implement the program. Table 6-2 presents an estimate of potentially collectible
dra i nage fees .
TABLE 6-2
Dra inage
Area
Cook
Del Safari
Frank Sinatra
�'' Monterey (North)
Portola/Hovely
Portola (North)
Rebecca
TOTA LS
*Overall average
�':
POTENTIALLY COLLECTABLE
DRAINAGE FEES
Percentage
Undeveloped
Tota I
Cost
Cost Allocable
to Developments
780
1000
100 0
100 0
47 0
100 0
100°0
84 0*
$ 2,300,000
600,000
2,250,000
400,000
4,970,000
910,000
3,750,000
$15,200,000
$ 1,795,000
600,000
2,250,000
400,000
2,335,000
910,000
3,750,000
$12,040,000
34
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�
It is recommended that drainage fees be reviewed annually and adjusted
to reflect then current construction costs. This can be readily accomplished
�" if the ordinance adopting drainage fees ties annual adjustments to some recog-
nized cost index (e.g. , ENR or Bureau of Reclamation indicies) .
It should also be noted that no cost for drainage easements has been
included in the project cost estimates. It has been assumed that dedication of
„� such easements would be a condition of development. The City has, on occasion,
accepted dedication of drainage facilities satisfying master plan requirements in
lieu of drainage fees. However, it is recommended that either:
(1) The unit drainage fees be increased to provide for
purchase or credit for rights-of-way; or
(2) Dedication of drainage easements be made a condition
of development and no credit be given for right-of-way
in lieu of fees.
6.3 - Federal/State Assistance Programs
There are a number of Federal or State programs which provide financial
assistance to local communities for the development of needed facilities. The
;,�, City currently receives an allotment of funds under the Housing and Community
Development Act of 1974. These HCDA monies could be potentially utilized to
construct certain portions of the drainage systems. However, because of the
limited funding available and the demand for other community facilities, it
probably cannot be considered a primary source of funding. Many of the other
" Federal programs are geared to assist communities with lower per capita incomes
� or where the nature of the community is less urbanized.
6.4 - Assessment Districts
Assessment district proceedings offer a variety of inethods of financing
storm drain systems under the Acts of 1911, 1915, or other assessment pro-
ceedings. Assessment district financing could be used for funding in local
drainage areas, particularly those which are now substantially developed.
However, the establishment of an assessment district requires that property
owners within the area recognize the problem and agree to the assessment
approach to facility financing.
�
35
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Assessment districts, like most other methods of municipal financing, have
been affected by the passage of Proposition 13. Certain cases now being consi-
�► dered by the courts may affect the viability of assessment proceedings for the
funding of future municipal improvements.
6.5 - Combinations of Funding Methods
It is unlikely that any one single financing method will be sufficient to
provide the funding necessary to implement the master drainage plan. Of the
several methods reviewed previously, it appears that drainage fees c�uld pro-
vide the largest single source of revenue, nearly 80$ of the total project cost.
It will, however, be necessary for additional monies to be generated from other
sources. Whether these be from federal grant programs or from some other
means, the funding of these remaining improvements will be of significant im-
portance to the successful implementation of the program.
vr
36
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