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FPUP Application Guide

Single-Lot Floodplain Use Permits

A floodplain use permit is a document issued by the District that authorizes a specific improvement within unincorporated Pima County within a regulatory floodplain or erosion hazard area, as well as within mapped riparian habitat. Regulatory floodplains include areas along any wash with a base flood discharge that equals or exceeds 100 cubic feet per second, and areas subject to sheet flooding.

The purpose of the permit process is to minimize the likelihood of damages to buildings or improvements in the event of a flood. The regulations are also enforced to ensure that proposed improvements do not cause flooding problems for downstream -- or upstream -- neighbors.  Since riparian habitat is important for flood hazard mitigation and for the preservation of wildlife and ecosystems that are key to maintaining Pima County’s natural resources, the District regulates the preservation of riparian habitat.

Virtually all man-made structures or improvements constructed within regulatory floodplains or erosion hazard areas require Floodplain Use Permits or floodplain approval prior to beginning construction. These include: all structures, additions, fencing, walls, pools, drainage improvements or modifications, erosion control measures, and some temporary construction.

Before issuing a Floodplain Use Permit, District staff undertakes a detailed review of the hydrologic conditions that affect the subject property, and then checks to make sure that any proposed improvements are in conformance with the County's Floodplain and Erosion Hazard Management Ordinance. Due to the comprehensive nature of the review, please be advised that floodplain use permits may take several weeks to complete.

Please bear in mind that your project or activity may require the review and approval of other County departments. The Development Services Department provides a quick reference guide for what requires permits.

Site Plans

Example site planIn order for the District to adequately evaluate a proposed improvement, a complete and accurate site plan, drawn to a standard engineering scale, is required.  An example site plan is provided in Technical Procedure 102 to help you create a good site plan.

Some of the requirements are as follows. The site plan must:

  • Accurately represent the property boundaries and all proposed and existing improvements using a standard engineering scale. Acceptable scales are limited to: 1"=20', 1"=30', 1"=40', 1"=50', 1"=60', 1"=100', or multiples of 100 up to 1"=600'. For large properties, 1"=1000' or greater may be used, but a more detailed drawing of the area of work may be required.
  • Accurately state the scale of the map elements.
  • Contain a North arrow.
  • Provide information that identifies the property (address, tax code, etc.)
  • Show and label all existing and proposed improvements, to scale and properly dimensioned, including structures, septic systems, fences, walls, shade structures, berms, ditches, driveways, grading, or any other manmade feature that may divert, retard, or obstruct flow.
  • Show the extents of any fill pad. Unless an alternative is approved by the District, fill pads for structures must extend a minimum of 10 feet from the edge of the structure.
  • Show and label tops of banks of all regulatory washes on or near the property, where applicable.
  • Show and label floodplain boundaries, erosion hazard setback limits, and riparian habitat boundaries, where applicable.
  • Show any additional details, such as the locations of flood openings in structures or walls, side views of fences/walls, etc., when applicable
  • Details of flood resistant materials used in the construction of structures that are to be floodproofed.

Please see Technical Procedure 102 for more details on site plan requirements.

Construction Methods

Orientation

Floodwaters exert tremendous force upon objects which obstruct their flow, therefore the Ordinance requires that all structures with a long axis be oriented with the long axis parallel to the direction of flow. Floodwaters exert tremendous force upon objects that obstruct its flow, so reducing the area perpendicular to the direction of flow significantly reduces the flood forces that the structure must withstand. Orienting structures parallel to flow also reduces the erosion potential of floodwaters at the structure.

Flood Resistant Materials

For all structures and all methods of elevation, it is important to ensure that materials that may be exposed to flood waters are resistant to flood damage. The District requires the use of flood-resistant materials below the Regulatory Flood Elevation (RFE) on all structures. All materials below the RFE must be flood-resistant, not just the structural components. The best and easiest way to accomplish this is to use only masonry (block, brick) or steel below the RFE. Pressure treated or naturally decay resistant wood is also acceptable. Standard construction products such as untreated lumber and drywall are not acceptable for use below the RFE. More information is available in Technical Policy 021. Please visit the District if you have any questions about the use of flood resistant materials.

Method of Elevation

Protecting structures from flood hazards is one of the District's primary responsibilities. The District accomplishes this by elevating structures above flood waters, and minimizing the obstruction to flow caused by the structure, along with other methods discussed in later sections.

Some potential methods of elevation are similar for both manufactured homes and site-built structures, others are impractical or uncommon.

It is important to note that service facilities such as air conditioning units, water heaters, and furnaces must also be elevated to prevent damage from flood waters.

Pilings or Piers (Manufactured Homes)

Elevating on pilings or piers is a common method for elevating manufactured homes, and is occasionally used to elevate site-built structures or additions to manufactured homes. This elevation method is usually the best method for elevating structures within a floodplain because they offer the least obstruction to flow, allowing floodwaters to pass underneath the structure with little or no resistance. The force of moving water can be significant and like any moving object, it resists changing direction due to it's momentum. Pilings and piers are the most "invisible" to flood waters.

In floodprone areas, flood depths, velocities, and/or soil types lead to the potential for floodwaters to undermine pilings or piers, therefore it is necessary to toe-down the base of the pilings or piers below grade to a certain depth. Common toe-down depths below natural grade range from 18 inches to 30 inches. Toe-down depths may also be established by a civil engineer. You are encouraged to visit the District to determine what toe-down requirements will be placed on your improvement before getting bids from contractors or providing bids to clients to ensure that the true cost of construction is included.  More information about construction on piers can be found in Technical Policy 003.

Stem Walls (Manufactured Homes and Site Built Structures)

There are two ways to elevate a structure on a stem wall, with a crawl space or with the area behind the stem wall being back-filled. From an obstruction to flow perspective, stem walls are the best method of elevation for site-built structures and the second best method of elevation for manufactured homes. Since stem walls do divert flow, there is greater potential for erosion to undermine the foundation, and thus stem walls must always be toed-down below natural grade at least 18 inches, but potentially to greater depths depending on the location and orientation of the structure, the soil type, and the depth and velocity of the flood.

Due to non-floodplain related crawl space requirements for manufactured homes, stem walls must be crawl space type. If the area behind the stem wall is not backfilled, such as is the case with all manufactured homes and occasionally with site-built structures, the stem wall must have adequate flood openings to ensure that the force of water on the outside of the stem wall doesn't exert enough force to cause structural failure of the stem wall. Allowing water to reach equilibrium on both sides of the stem wall equalizes the hydrostatic pressure. Guidelines for flood openings are addressed in Technical Policy 022.

If the area behind the stem wall is backfilled, no flood openings are required, as the backfill acts against the pressure of the flood waters.

Fill Pads (Manufactured Homes and Site Built Structures)

The floodplain ordinance for Pima County requires that fill pads within the floodplain extend 10 feet from the edge of a structure at the base flood elevation and be adequately protected from erosion by rip-rap toed-down below natural grade or other approved methods, unless an alternative method, designed by an Arizona registered civil engineer at the owner's expense, is approved by the District. Since fill pads increase the obstruction to flow and take up more volume of the floodplain, they are the most likely method of elevation to increase the flood damage potential for adjacent properties. The use of fill pads may be limited or restricted in some circumstances. Technical Policy 006 provides additional guidance on the use of fill pads.

Erosion Hazard Setbacks

Water is only one of the hazards associated with flooding. Any time water is moving, it has the potential to cause erosion. As exemplified during the 1983 flood on the Rillito River, houses that were well above the flood waters were nonetheless destroyed as the river eroded it's banks, migrating to and eventually undercutting structures, which then fell into the river. The same phenomenon can and does occur on virtually all washes. Over time, nearly all washes will erode their banks and migrate to a certain extent. The ability of a wash to migrate depends on many factors, including the discharge, depth and velocity of the water, the soil or other material that the wash is flowing through, and type and density of vegetation along the banks of the wash. As a result, the floodplain ordinance also contains provisons designed to protect structures from erosion from regulatory washes.

It is important to note that all washes have floodplain and erosion hazards, and all regulatory washes (any wash having a discharge of 100 cubic feet per second or greater) have a regulatory erosion hazard setback, whether there is a mapped floodplain associated with the wash or not.

The ordinance focuses on the discharge of the wash as a representative value for erosion potential. Regulatory washes with higher discharges have a generally greater ability to erode banks, and thus require greater setbacks from the wash to protect structures. Currently, standard erosion hazard setbacks range from 25 feet for relatively small regulatory washes up to 500 feet on major watercourses where bank protection is not present. In most cases, erosion hazard setbacks are measured from the top of the bank of the wash.

It is possible to reduce the erosion hazard setback for a particular property or improvement by either demonstrating to the District that the default setback is overly conservative or by designing and constructing engineered erosion protection measures. This analysis must be completed by an Arizona registered civil engineer and must be submitted to the District as part of an FPUP for District review and approval. Please have your engineer use the Technical Policy 020: Engineering Analysis Requirements for Determining an Alternative Safe Erosion Hazard Setback Limit to assist in preparing the analysis.

An important point to make here is that erosion hazard setbacks apply to structures and septic systems, not to walls, fences, ramadas, swimming pools, and the like. Since these other improvements may get damaged by erosion and cause other damage if they fail, it is highly recommended that all improvements on a property be placed outside of the erosion hazard area, but it is seldom required. Property owners should be prepared to have to repair or replace any improvement placed within the erosion hazard area.

For the convenience of our customers, the District maintains a List of Engineers who have successfully submitted reports for Floodplain Use Permits.

Minimizing Adverse Impacts

Any activity within a floodplain that takes up space or diverts water from it's natural path has the potential to adversely impact adjacent properties, or even your own property and welfare. It is therefore important to minimize adverse impacts to the floodplain. Living in a floodprone area means that there will be certain restrictions on what one can do on the property. Completely removing your property from flooding by adding fill or surrounding the property with a block wall is not allowed because doing so increases the flooding on adjacent properties. You have the right to develop your property only so far as you do not cause harm to others. When developing or improving your property, please keep the following things in mind:

  • Locate improvements on the highest ground on the property. That's where the least amount of water will be.
  • It is wise, and may be required, to reduce the size of major obstructions to flow such as walls and fences.
  • Aligning improvements in the direction of flow will minimize the diversion of water, maintaining more of the natural flow of the floodplain and making the improvement safer by impounding less water behind it.
  • Design improvements so that water can pass underneath them whenever possible.
  • Minimize the amount of grading, clearing, or grubbing on your property. Graded areas often divert flow, and areas cleared of vegetation often promote erosion and formation of new washes.

Covenants

Most permits issued by the District require the current property owner(s) to sign Covenants and Restrictions Running with the land (covenants).  There are three types of covenants, General, Specific and Access.  Each type of covenant is described below.  More information can be found in Technical Procedure 103.

Covenants must be signed by any and all current property owner(s)  in front of a Notary Public and thus require the District to obtain the latest recorded deed for the property.  If the District is unable to obtain the latest recorded deed electronically from the Pima County Recorder's office, it will be necessary for the applicant or property owner to supply the deed to the District.  A list of acceptable deed types can be found in Technical Procedure 103.  Due to Pima County Recorder's office requirements for document legibility, font size and document margins, the District may not accept photocopies or copies that have been Faxed at any time.

General Covenants

General covenants are required when the District approves a permit for any activity on a property that is impacted by a regulatory floodplain. General covenants require all property owners to acknowledge that:

  • uses of the property are restricted by a Floodplain Use Permit (FPUP)
  • all or part of the property is impacted by a floodplain and/or erosion hazard and, as such, any improvements may be subject to damage
  • an FPUP will be obtained for all activities requiring an FPUP
  • natural drainage will not be altered without the express written approval of the District
  • Owner(s) assume full responsibility for their actions and shall hold Pima County and the District harmless.

Specific Covenants

Specific covenants are generally appended to General covenants, and as the name implies, are specific to the activity being permitted.  Examples of specific covenants are:

  • Elevating a fence at or above the Base Flood Elevation
  • Maintaining openings in a block wall to be free of debris
  • Maintaining flood openings in a structure
  • Inspecting and maintaining erosion protection
  • Maintaining vegetation planted under a Riparian Habitat Mitigation Plan

Access Covenants

Access Covenants are required when unpaved and/or not publicly maintained roadways necessary to access the property are within a regulatory floodplain.  The area of applicability for Access covenants is from the end of a paved, publicly maintained roadway to the property line of the property for which the permit is being obtained.  Access covenants entail the property owner acknowledging that:

  1. owner(s) and guests may not have access to and from the property in times of flooding
  2. emergency vehicles may not have access to and from the property in times of flooding
  3. neither Pima County nor the District are responsible for maintaining the unpaved and/or unmaintained access and holds both entities harmless
  4. owner(s) are responsible for notifying users of the property that vehicular access may be impossible and/or hazardous during times of flooding.  The District recommends that signs be erected, but signs are not required.  Notification, however, is required.

Access covenants are required under the following circumstances:

  • If, after leaving a publicly maintained paved roadway, it is necessary to cross a regulatory floodplain on a private road or easement (whether paved or unpaved) before getting to the property.
  • If, after leaving a publicly maintained paved roadway, it is necessary to cross a regulatory floodplain on a dirt road or easement (whether public or private) before getting to the property.

Access covenants are NOT required under the following circumstances:

  • If the property is accessible directly from a paved, publicly maintained roadway.
  • If access to the property requires driving through a regulatory floodplain on a paved, publicly maintained roadway but the unpaved and/or unmaintained portion of the access to the property does not cross a regulatory floodplain.

Engineering

There are some areas within Pima County in which the flood and/or erosion hazards are unknown or are significant enough to warrant the requirement that the propety owner obtain the services of an Arizona registered civil engineer to either determine the extent of the hazards and demonstrate that the proposed improvements are safe from that hazard, or to design structural protections for the improvement. The engineering analysis must be submitted to the District for review and approval. Please be advised that FPUP review and approval times will be longer due to the highly technical nature of the review of these reports. Placing improvements in locations that require an engineering analysis should be avoided if at all possible, therefore it is recommended that you discuss your plans with the District during the planning stages of the project in order to site the project in the least hazardous location on the property.

For the convenience of our customers, the District maintains a List of Engineers who have successfully submitted reports for Floodplain Use Permits.

Elevation Certificates and As-Built Certifications

Commonly, a Floodplain Use Permit for a structure will have an elevation requirement. In these cases, the Floodplain Ordinance requires that an Arizona registered land surveyor or Arizona registered civil engineer complete an Elevation Certificate demonstrating that the structure and all associated service equipment (air conditioning units, water heaters, furnaces, etc.) are adequately elevated and that flood openings, if required, are constructed properly. The Elevation Certificate form will be provided to you by the District at the time of issuance, but it is your responsibility to contract privately for the service of completing the form. The District currently ensures the return of Elevation Certificates by placing holds on certain inspections until a correct and complete Elevation Certificate is returned to, and approved by, the District. Only Elevation Certificates containing the surveyor's original signature and seal will be accepted by the District.  For the convenience of our customers, the District maintains a List of Surveyors who have attended a recent Elevation Certificate Workshop.

If the elevation requirement for your permit is based upon natural grade and natural grade is going to be disturbed by the project, it may be necessary to have the surveyor or engineer perform a site visit to obtain pre-disturbance information that will be necessary later to demonstrate that the structure is in compliance with the permit conditions.

If your permit requires the construction of engineered structural improvements to protect your property from flooding or erosion hazards, an As-Built Certification is required. This certification must be completed by an Arizona registered civil engineer, and is generally completed by the engineer that performed the design. The District currently ensures the return of As-Built Certifications by placing holds on certain inspections until a correct and complete certification is returned to, and approved by, the District. Only As-Built Certificates containing the engineer's original signature and seal will be accepted by the District.

It may be necessary for the engineer to view the construction of engineered improvements at various times during the construction of those improvements. For example, if it is necessary to toe-down an erosion cut-off wall down a certain depth below natural grade, the engineer must verify the depth of the cut-off wall before the trench for the wall is backfilled. Please coordinate such inspections with the engineer.

It may take several days for the District to review and approve these certifications, and thus release the inspection holds that allow you to proceed with your project. To avoid delays, have your surveryor or engineer perform the site visit and complete the form as soon as possible after the necessary work has been completed. Make sure you understand when all of the above certificates need to be returned to the District in order to avoid delays in your construction and inspection process.

Minimizing Disturbance to Riparian Habitat

Due to it's association with floodplains and importance in mitigating flood-related hazards, the District also regulates disturbance to mapped riparian habitat. The mapping effort was conducted in conjunction with the Sonoran Desert Conservation Plan approved by the Board of Supervisors in 1998 in part to comply with federal regulations. The floodplain ordinance does not prohibit all development within riparian habitat, but it does place certain restrictions on development.

Permitting Violations

In the case of existing improvements constructed within a floodplain without a permit, additional requirements may be applied in order to obtain a permit. For unpermitted structures, it will be necessary to demonstrate whether the structure conforms to the ordinance or not. If it does not conform to the ordinance, it will be necessary to provide the District with a report from an Arizona registered civil engineer that either demonstrates that the structure is safe from flood related hazards, or designs flood and/or erosion protection for the structure. If flood protection measures are required, then in most cases the flood protection must be constructed and approved prior to the issuance of any permits. This is done to ensure that the violation is corrected prior to the issuance of permits.