In large part, the Stormwater Master Plan has been crafted based upon the recommended stormwater management alternative for each of the 59 TSMS watersheds.
These recommended stormwater management alternatives were presented in the TSMS, Phase II, Task 9 document Watershed-Specific Alternatives Analysis and Evaluation Report .
The 59 watershed-specific stormwater management alternatives have certain common elements which can be grouped into five major categories of both nonstructural and structural stormwater management measures: (1) Preservation of Naturally Vegetated Watercourses (nonstructural); (2) Flood Hazard Studies (nonstructural); (3) Stormwater Quality Investigations (nonstructural); (4) Stormwater Capital Improvement Projects (structural); and (5) Miscellaneous Capital Projects (structural).
To assure a comprehensive, watershed-wide approach for management of the stormwater system, two or more stormwater management alternatives were formulated for each watershed to address the potential flooding hazards within each watershed; then the system-wide impacts of the formulated stormwater management alternatives were analyzed based on pre-determined social, environmental, economic, and technical factors; and finally the relative effectiveness of the watershed-specific alternatives were evaluated according to the analysis which was performed.
The common elements of the 59 recommended watershed-specific stormwater management alternatives have been grouped into five major components for the purpose of (1) identifying the relative significance of each component; (2) identifying the overall effects and potential impacts; and (3) assessing the implementability of each component, all on a City-wide basis.
Since it may not be possible to implement all elements immediately, prioritization schemes for each of the five major components were developed.
Methodologies for prioritizing (1) the naturally vegetated watercourses recommended for preservation; (2) Flood Hazard Studies; and (3) Stormwater Quality Investigations were developed by the Project Team with input from the TSMS advisory committees.
The actual prioritization was accomplished by the Project Team.
In contrast, the prioritization of the Stormwater Capital Improvement Projects was performed by the Stormwater Capital Improvement Project Prioritization Committee utilizing a methodology developed by the Project Team.
This Prioritization Committee consisted of members of the Project Team, City staff, City Council Aides, and representatives from the TSMS advisory committees. Miscellaneous Capital Projects were prioritized, where appropriate, by the Project Team and City staff.
Riparian habitat along the naturally vegetated watercourses within the City has been identified and tabulated within the TSMS, Phase II report titled Natural Riparian Habitat Inventory .
All of the naturally vegetated watercourses containing riparian habitat, with the exception of approximately 10 acres that may be disturbed as the result of several proposed Stormwater Capital Improvement Projects, have been identified as candidates for preservation in accordance with the goals and objectives of the Stormwater Master Plan.
These goals and objectives were defined in the TSMS, Phase II, Task 5 "Planning Criteria Document".
The goals and objectives were based, in part, on Mayor and Council Resolution No. 15269 (March 29, 1990), which states that "The Mayor and Council find that protection and preservation of natural drainage systems should be the primary emphasis of City stormwater management efforts. Nonstructural solutions to flooding hazards shall be the preferred strategy over structural solutions."
Table 3 of this report summarizes the amounts of riparian habitat that are recommended for preservation for each of the six Hydrologic Units within the City. Table 3 of this report also shows the area that may be disturbed and require mitigation as the result of a Stormwater Capital Improvement Project. Approximately 98% of the riparian habitat that has been identified along naturally vegetated watercourses within the City is recommended for preservation.
The watercourses identified for preservation are considered at this time to be candidates for preservation. No detailed environmental assessment of the relative environmental value of each watercourse segment has been conducted, nor has any inventory of the right-of-way or land ownership along these naturally vegetated watercourses been compiled.
In addition, no administrative policy, ordinance, zoning regulation, or land acquisition program currently exists which guarantees the preservation of these naturally vegetated watercourses.
Possible strategies for implementing a preservation program for these naturally vegetated watercourses are discussed in more detail in Section V of this report.
While all riparian habitat not disturbed by a proposed Stormwater Capital Improvement Project is recommended for preservation, measures cannot be taken to preserve all of the watercourses at one time due to economic or regulatory constraints.
In addition, certain watercourses or watercourse segments may be preserved prior to others.
To address these factors, a methodology for prioritizing the riparian habitat was developed, for both watercourses and individual watercourse segments, as a planning tool to guide future preservation efforts.
Table 4 of this report presents a prioritized list of the watercourses and watercourse tributaries.
Table 5 of this report shows the prioritized list of individual watercourse segments, categorized by riparian class.
Initially, each continuous segment of riparian habitat along a naturally vegetated watercourse was scored according to habitat type, area of habitat, cultural resources along the watercourse segment, and other environmental values.
The scores for watercourses and watercourse tributaries were determined as the sum of the individual segment scores, multiplied times a connectivity factor. The prioritization methodology and corresponding results are discussed in more detail in the TSMS, Phase II document "Preservation Tools and Strategy Report".
Due to high levels of both social acceptability, environmental compatibility, and economic feasibility, nonstructural stormwater management measures, such as the purchase of flood insurance as part of the National Flood Insurance Program, have been emphasized whenever and wherever practicable to do so.
Accordingly, the potential flooding of approximately 1808 homes within the City has been addressed not by structural flood-control measures; but rather by a recommendation that flood insurance be purchased by individual homeowners (or purchased by renters for home contents) as protection against large monetary losses resulting from flood damages.
As a part of adopting a comprehensive approach to nonstructural stormwater management, it is proposed that detailed Flood Hazard Studies be conducted by the City for those areas where flood insurance is recommended. Such studies are proposed in order to better define the extent of flooding potential.
It is also recommended that the Flood Hazard Studies include provisions for public education, with the City notifying both property owners and residents in affected floodprone areas of potential flooding hazards.
Possible nonstructural stormwater management measures, in addition to the purchase of flood insurance, that each individual property owner or resident could undertake in order to protect themselves and their property, would also be an element of the public education component of Flood Hazard Studies.
A general Scope of Work for these proposed Flood Hazard Studies will be provided as part of the Final Report for the Stormwater Master Plan.
Since it is likely that recommended Flood Hazard Studies will be conducted for individual watercourses, and not as a City-wide study of all watercourses, a prioritization methodology was developed for ranking watershed-specific Flood Hazard Studies.
The results of this prioritization are summarized in Table 6 of this report. A Prioritization Index was defined to be a measure of the relative cost effectiveness of each individual Flood Hazard Study.
The Prioritization Index is calculated as the ratio of the area of floodprone buildings along the watercourse to the estimated cost of performing each study.
The amount of floodprone buildings was determined from the total area, in square feet, of the residential homes and other buildings which are located in areas of high density land uses (i.e., residential, commercial, and industrial). The estimated cost of the study is based on an average unit cost (dollars per mile) determined from similar studies. Actual costs of performing the Flood Hazard Studies will depend on the level of detail desired; and, for very short and very long watercourses, may likely vary from the average unit cost estimates used to develop the Prioritization Index.
As part of the Stormwater Master Plan, Stormwater Quality Investigations have been identified as one possible way to address both existing and future stormwater quality concerns within the City.
Stormwater Quality Investigations may consist of one or more of the following items: (1) stormwater quality sampling; (2) more detailed land-use characterizations; (3) investigations into specific chemical/material usage at facilities within each watershed; (4) identification of existing BMPs; and (5) evaluation of the potential impacts of stormwater runoff on the quality of the ground water within the regional aquifer.
Other possible techniques include Best Management Practices (BMPs) and New-Development Controls, which could be utilized to both protect and enhance stormwater quality. BMPs and New-Development Controls have been discussed in more detail in the TSMS, Phase II report "Stormwater Quality BMPs, New- Development Control Recommendations".
A prioritization scheme was developed in order to identify the individual watersheds within the City that represent a greater concern with regard to potential stormwater quality issues.
In general, the objective prioritization methodology incorporates (1) contaminant loadings determined from modeling results; (2) potential sources of stormwater constituents in excess of that predicted by the land-use based modeling; (3) environmental sensitivity of a watershed; and (4) potential implementation of stormwater quality controls. The prioritization methodology and results are presented in detail in the TSMS, Phase II Technical Memorandum titled: Watershed Stormwater Quality Prioritization .
The prioritized list of potential Stormwater Quality Investigations is presented in Table 7 of this report.
If Stormwater Quality Investigations prove to be a necessary and viable approach to address stormwater quality concerns, then initial investigations would be considered for the highest ranked watersheds. At the present time, no significant problems with the quality of stormwater runoff within the City have been documented.
Stormwater Quality Investigations would only be implemented if warranted by the ongoing stormwater management program.
The major structural component of the Stormwater Master Plan consists of 47 Stormwater Capital Improvement Projects which generally involve channelization, watercourse bank protection, storm drains, and detention/retention facilities.
These projects were compiled based on the recommended stormwater management alternatives presented in the TSMS, Phase II, Task 9 "Watershed-Specific Alternatives Analysis and Evaluation Report". The analysis and evaluation of these recommended stormwater management alternatives was completed by the Project Team in conjunction with City staff and the TSMS advisory committees.
Comparative rankings of the Stormwater Capital Improvement Projects were determined by the Stormwater Capital Improvement Project Prioritization Committee, made up by members of the Project Team, City staff, City Council Aides, and representatives from the TSMS advisory committees. The comparative rankings were subsequently used for crafting a series of 5-year Stormwater Capital Improvement Programs.
The results of the rankings, project descriptions, Ward locations, information regarding existing flooding hazards, project costs, and other economic data are presented in Table 8 of this report.
The estimated costs of the Stormwater Capital Improvement Projects have been refined from the project costs that were presented in the TSMS, Phase II, Task 9 "Watershed-Specific Alternatives Analysis and Evaluation Report".
In that document, project design and corresponding costs were developed strictly at a concept/planning level, and were used only for comparing the relative costs of stormwater management alternatives that were being analyzed for each watershed.
The procedure that was used for the Task 9 analysis to estimate capital, operating, and maintenance costs for the Stormwater Capital Improvement Projects was originally presented in the Task 6 "Watershed-Specific Criteria Document".
Unit construction costs were developed based on 1993 City bid tabulations for projects designed and constructed to City standards.
Allowances were made for construction contingencies; as well as engineering, administrative, legal, and financial costs.
Due to a lack of any reliable data regarding existing City right-of-way and property ownership, right-of-way costs were not included in the Task 9 analysis for any of the projects, with the exception of the proposed detention/retention facilities.
As can be expected with any procedure utilizing average unit costs, the reliability of such a procedure for cost estimating decreases for those projects that are not "average" in nature; ( i.e., small projects, large projects, projects requiring substantial roadway modifications, projects requiring substantial right-of-way acquisition, and projects with innovative or unusual elements). In addition, the proposed Stormwater Capital Improvement Projects were formulated at a planning level only; and final, detailed project designs will certainly result in adjustments to the scope of each project.
For future programming purposes, costs of the recommended Stormwater Capital Improvement Projects were revised to account for anticipated right-of-way needs. However, the costs still represent "average" project conditions, and actual costs may deviate due to final design considerations and other unforeseen circumstances.
Preliminary 5-year Stormwater Capital Improvement Programs have been crafted based on (1) the comparative rankings determined by the Stormwater Capital Improvement Project Prioritization Committee, (2) an assessment of the relative benefits and costs of each Project, (3) the relative cost of each project, and (4) geographic distribution (Ward location) within the City of Tucson.
Each 5-year Program is relatively balanced in terms of the total 5-year cost, a mixture of both large and small projects, and geographic distribution. Table 9 of this report summarizes the six recommended Stormwater Capital Improvement Programs for the years 1995 through 2025.
Subsections A. through D. of Section II of this report describe the first four major components of the Stormwater Master Plan which have been developed as part of a comprehensive, watershed-wide approach for stormwater management within each of the 59 TSMS watersheds located within the City.
These four components are: (1) Preservation of Naturally Vegetated Watercourses; (2) Flood Hazard Studies; (3) Stormwater Quality Investigations; and (4) Stormwater Capital Improvement Projects.
The need for various smaller projects have been identified within each watershed; but the projects are generally isolated, localized, and relatively insignificant in terms of overall cost and the magnitude of flooding hazards the projects are designed to address.
In contrast, the 47 Stormwater Capital Improvement Projects presented in Section II.D. of this report require substantial funding, and have been developed to address more widespread flooding problems within the watersheds.
Nevertheless, these localized projects are an integral part of the Stormwater Master Plan because they address both existing and potential flooding concerns, although at a much smaller scale.
These Miscellaneous Capital Projects can be categorized into the following groups: (1) Roadway Culverts; (2) Potential Localized ("SPOT") Projects; and (3) Grade-Control Structures.
Each individual Miscellaneous Capital Project has been presented in the TSMS, Phase II "Watershed-Specific Alternatives Analysis and Evaluation Report" as (1) an element of a recommended stormwater management alternative, or (2) a potential localized stormwater project.
Throughout the City there are existing roadway culverts and dip sections that do not meet current drainage and roadway standards for conveying stormwater runoff.
Stormwater runoff at these culverts and dip sections can interfere with the normal flow of traffic, as well as pose a potential threat to public safety during times of heavy rainfall.
It is recommended that many of these substandard roadway culverts and dip sections be replaced with new roadway culverts that meet current City drainage and roadway standards.
The existing culverts and dip sections recommended for replacement have been prioritized using a Culvert Prioritization Index, which is calculated as a function of Average Daily Traffic, capacity of the existing culverts to convey stormwater runoff, and depth and velocity of flow in the existing dip sections. The results of this prioritization are presented in Table 10 of this report.
Potential Localized ("SPOT") Projects were not formulated as part of the watershed-wide stormwater management alternatives because they address isolated, localized problems which may not be representative of overall conditions within the watershed.
These projects are recommended for future consideration, and are listed in Table 11 of this report for both stormwater quantity and quality projects.
Grade-control structures have been identified as appropriate measures for erosion mitigation along watercourses where (a) erosion has been identified as an existing problem; and (b) potential erosion along naturally vegetated watercourses may result due to stormwater runoff from existing or future urbanization.
In most cases, these grade-control structures have been identified based on a qualitative, planning level of analysis.
Before any specific projects are proposed, a more detailed analysis is recommended for those watercourses listed in Table 12 of this report. Table 12 presents a list of the watercourses where grade-control structures may be necessary, along with an estimate of the possible costs of these structures and any ancillary structural elements necessary in conjunction with their construction.
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