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Question 5 - Impact on Flooding - Full EAF (Part 2)

Full Environmental Assessment Form (FEAF) Workbook

The proposed action may result in development on lands subject to flooding.

A flood scene with houses and trees

Floodplains are low-lying lands next to rivers and streams. When left in a natural state, floodplain systems store and dissipate floods without adverse impacts on humans, buildings, roads and other infrastructure. Natural floodplains add to our quality of life by providing open space, habitat for wildlife, fertile land for agriculture, and opportunities for fishing, hiking and biking.

Floodplains can be viewed as a type of natural infrastructure that can provide a safety zone between people and the damaging waters of a flood. But more and more buildings, roads, and parking lots are being built where forests and meadows used to be which decreases the land's natural ability to store and absorb water. Coupled with changing weather patterns, this construction can make floods more severe and increase everyone's chance of being flooded.

Some projects may be outside of a floodplain, but still be in an area with known flooding history. Some projects that disturb more than one-acre may be required to have a stormwater pollution prevention plan (SWPPP) and will need to include engineered or site designed methods to control stormwater. Development proposed in a floodway or floodplain will need to meet State or local regulations. For more information, see the DEC Floodplain Construction Requirements page.

To answer this question

Review Part 1 questions D.1.h., E.1.e., E.2.e., E.2.h., E.2.i., E.2.j., and E.2.k.

Lands subject to flooding can include:

  • Lands in a floodway or floodplain.
  • Lands in wetlands or in areas where the water table is less than 3 feet.
  • Lands where development will change drainage patterns so as to create the potential for flooding.

If the proposed action will not result in any development of lands subject to flooding, then check 'No' and move to question 6. If the proposed action will result in development of lands subject to flooding, check 'Yes' and answer sub-questions (a) through (g).

Identifying potential impacts

The reviewing agency should evaluate the following sub-questions and decide if there will be any impact. If there will be an impact, the reviewing agency must then evaluate the magnitude of that impact, and decide if the impact will be small or moderate to large. This will depend on the overall scale and context of the proposed project as described in the Introduction to Part 2. The reviewing agency should be reasonable when conducting this review.

  • If the proposed project exceeds a numeric threshold in a question, it is presumed to be a moderate to large impact.
  • If the proposed project does not exceed a numeric threshold in a question, the reviewing agency should consider the scale and context of the project in determining if an impact may be small or moderate to large.
  • These sub-questions are not meant to be exhaustive. The reviewing agency should use the "Other impacts:" sub-question to include any additional elements they feel need to be analyzed for potential impacts.

a. The proposed action may result in development in a designated floodway.

The floodway is that area that must be kept open to convey flood waters downstream. Within an "AE" zone or a numbered "A" zone on a floodplain map, there may be an area known as the "regulatory floodway," which is the channel of a river and adjacent land areas which must be reserved to discharge the 100-year flood without causing a rise in flood elevations. No development is allowed unless the developer has first proven that the development will not increase flood elevations at any location during the 100-year flood.

Applicable Part 1 Information

E.2.i.

Analysis

  • Is any part of the proposed action located within the floodway?
  • Does the proposal meet the requirements of the local municipality's floodplain management law or ordinance?
  • If yes, what type of development or land disturbance is planned for the floodway?
  • Do the local floodplain regulations impose more stringent restrictions on floodway development than the State?
  • If land disturbance or development is proposed in the floodway, has the developer conducted studies to prove flood elevations will not be increased?

Will there be an impact?

If there is no land disturbance or development of any kind in the floodway, then there will be no related impacts. Check 'No or small impact may occur."

Small Impact:

Some proposed projects that include minor changes to the landscape with non-permanent structures placed in the floodway are likely to have only a small impact. An example would be:

  • Utility poles, posts or piers, or elevated structures designed to allow flow underneath.
Moderate to Large Impact:

It is likely that one or more moderate to large impacts could occur under one or more of these circumstances:

  • Grading, fill, or land clearing takes place in the floodway.
  • Construction of any kind of permeable surface is planned in the floodway.
  • Construction of any structure that impedes or changes drainage patterns or water flow is planned in the floodway.
  • Construction of piers, weirs, docks, retaining walls, and other features that reach from land to water are planned in the floodway.
  • Riparian vegetation that grows from the water or bank edge (sometimes called stream side or lake side vegetation) is removed.

b. The proposed action may result in development within a 100 year floodplain.

A 100-year floodplain is the area that would be inundated by the 100-year flood. It is an area that has a one percent or greater chance of experiencing a flood in any single year. The 100-year floodplain is called a Special Flood Hazard Area and is shown on federal flood maps, known as Flood Insurance Rate Maps (FIRM). On the FIRM, these areas are shaded and labeled with the letter "A" or "V" sometimes followed by a number or letter.

In the coastal "V" zone, new construction and substantial improvement or substantially damaged structures must be elevated on pilings, columns or sheer walls such that the bottom of the lowest horizontal structural member supporting the lowest elevated floor is elevated to or above the base flood elevation plus two feet. Detailed standards exist regarding how to elevate the structure.


When there is a base flood elevation available, the lowest floor of any residential or commercial structure, including any basement, must be at or above the base flood elevation plus two feet. Alternatively, non-residential structures may be flood proofed in lieu of elevation. Every community should have a local flood plain administrator and questions on building in a floodplain should be directed to that office.

Applicable Part 1 Information

E.2.j.

Analysis

  • What land disturbance or construction will take place in the 100-year floodway?
  • Will the proposed project alter the flow of water or change drainage patterns into the water body?
  • What is the base flood elevation compared to the elevation of the structure and has the applicant calculated the base flood elevation?
  • Does the proposal meet requirements of the local municipality's floodplain management law or ordinance?
  • What flood protection is proposed?
  • What is the extent of recurring flooding in that location?
  • What is the vulnerability of existing and proposed development activities?
  • Are any other mitigation methods included in the proposed project to reduce flooding or flood damage?

Will there be an impact?

The absence of a stream, river, or lake on a property does not necessarily mean there will be no flooding on the property. Floodplains can extend for a distance beyond streams, rivers, lakes, and tidal waters.


If a stream, river or lake is on or near the property and there are no mapped floodplains and there is no history of flooding at the location, there will likely be no flooding impacts. Further, if there is a designated 100 year floodplain but the proposed project is not located in or near the floodplain, or does not change stormwater runoff or flows of water within that floodplain, there will likely be no flooding impacts. Check 'No, or small impact may occur."

Small Impact:

Proposed projects that include minor changes to the landscape, uses with pervious surfaces, structures built above base flood level, limited grading or clearing, or limited changes of drainage patterns in the 100-year floodplain are likely to have only a small impact. Examples would be:

  • Construction of any structure in the 100 year floodplain but it is built above base flood, plus 2 feet, pursuant to floodplain management regulations.
  • Land uses that include pervious surfaces such as gravel parking lots.
  • Land uses that do not change the flow of water or drainage patterns.
  • Limited clearing or grading activities.
Moderate to Large Impact:

It is likely that one or more moderate to large impacts could occur under one or more of these circumstances:

  • Construction of large expanses of impervious surfaces within the 100 year floodplain.
  • Clearing or grading, creation of walls or berms that alter the flow of water or drainage patterns.
  • Land uses that store chemicals or petroleum products above ground or below ground in areas subject to flooding.
  • Waste treatment or solid waste facilities located in the 100 year floodplain.
  • Alterations to surface water bodies with a designated 100 year floodplain in a manner which alters flow or drainage patterns.

c. The proposed action may result in development within a 500 year floodplain.

A 500-year floodplain is the area that would be inundated by the 500-year flood. It is an area that has a 0.2% chance of experiencing a flood in any single year.


Coastal "V" zones are particularly hazardous areas.

Applicable Part 1 Information

E.2.k.

Analysis

  • What land disturbance or construction will take place in the 500-year floodplain?
  • Will the proposed project alter the flow of water or change drainage patterns into the water body?
  • What is the base flood elevation compared to the elevation of the structure and has the applicant calculated the base flood elevation?
  • Will the development be protected to the 500 year flood elevation?
  • What is the extent of recurring flooding in that location?
  • What is the vulnerability of existing and proposed development activities?
  • Are any other mitigation methods included in the proposed project to reduce flooding or flood damage?

Will there be an impact?

As stated previously, the absence of a stream, river or lake on a property does not necessarily mean there will be no flooding on the property. Floodplains can extend for a distance beyond streams, rivers, lakes, and tidal waters.


If a stream, river or lake is on or near the property and there are no mapped floodplains and there is no history of flooding at the location, there will likely be no flooding impacts. Further, if there is a designated 500 year floodplain but the proposed project is not located in or near the floodplain, or does does not change stormwater runoff or flows of water within that floodplain, there will likely be no flooding impacts. Check 'No, or small impact may occur."

Small Impact:

Proposed projects that include minor changes to the landscape, uses with pervious surfaces, structures built above base flood level, limited grading or clearing, or limited changes of drainage patters in the 500-year floodplain are likely to have only a small impact. Examples would be:

  • Construction of any structure in the 500 year floodplain but it is built above base flood pursuant to floodplain management regulations.
  • Land uses that include pervious surfaces such as gravel parking lots.
  • Land uses that do not change the flow of water or drainage patterns.
  • Limited clearing or grading activities.
Moderate to Large Impact:

It is likely that one or more moderate to large impacts could occur under one or more of these circumstances:

  • Construction of large expanses of impervious surfaces within the 500 year floodplain.
  • Clearing or grading, creation of walls or berms that alter the flow of water or drainage patterns.
  • Land uses that store chemicals or petroleum products above ground or below ground.
  • Waste treatment or solid waste facilities located in the 500 year floodplain.
  • Alterations to surface water bodies with a designated 500 year floodplain in a manner which alters flow or drainage patterns.
  • Any development in a coastal "V" zone is likely to have a moderate to large impact.

d. The proposed action may result in, or require, modification of existing drainage patterns.

There are several actions that can modify existing drainage patterns. Any kind of change such as channeling, creation of impoundments, and stormwater increases or altered flow patterns are all actions that can modify drainage patterns of surface water flow. Stormwater runoff causes erosion but construction activities and land clearing can also change drainage patterns. The concern about altered drainage patterns is that it could adversely impact streams, rivers and lakes, or redirect coastal storm surges or wave actions. Altered flow can increase flooding and introduce more erosion and potential for pollution. If water is diverted from its normal flow, the opposite may occur: wetlands and streams may not receive as much water as needed to maintain the ecology and functioning as before. Drainage can be directed to stormwater drains,or to constructed bioretention, rain garden, or other storage and retention areas designed to slow water and allow sediments to settle out. When a large amount of stormwater is created, municipalities may need to construct a stormwater management system. Some stormwater may be directed into a water treatment facility that is already over-capacity. This can cause impacts when stormwater surges allow sewage to flow untreated into rivers and streams.

Applicable Part 1 Information

D.1.h., D.2.b., D.2.e., E.2.e., and E.2.h.

Analysis

  • Is any type of land disturbance or construction planned that would increase, decrease or change the flow of stormwater?
  • Will there be any increase in stormwater discharge from the site, and if so, how much?
  • Will there be a need for new stormwater retention ponds, or other stormwater management practices?
    • If there are stormwater discharges and no existing conveyance system, what are the plans to address stormwater and erosion from the site?
  • If Part 1 indicated that storm water discharges might flow to adjacent properties, where, how much, and what impacts might occur on the adjacent property.
  • If Part 1 indicated that there will be storm water discharges conveyed to established systems, is there enough capacity to handle the extra storm water?
    • Do the proposed plans include any upgrades or expansion to that system?
  • Is the project going to disturb more than one-acre of land and require a SWPPP and coverage under the stormwater general permit?
    • If it does not disturb more than one acre, but still has some land clearing, does the application include any erosion control and runoff controls?
  • Are there any protected water bodies or important surface drinking water supplies nearby that need to be protected from erosion and sedimentation (wetlands, reservoirs, protected streams)?
  • Are any stormwater reduction methods included such as minimizing impervious surfaces, using porous materials, or collecting and reusing stormwater?

Will there be an impact?

If there are no land disturbances or construction planned that would result in, or require, modification of existing drainage patterns, then there is no related impact. Check "No, or small impact may occur."

Small Impact:

Proposed projects that include minor changes to the drainage patterns are likely to have only a small impact. Examples would be:

  • Land uses with pervious surfaces that create limited stormwater runoff.
  • Where stormwater is contained on site and does not flow to or impact surface water bodies off-site on other properties.
  • Projects that are designed so that the amount of stormwater generated before construction is the same as afterwards. Projects that are designed using low impact development techniques for stormwater.
Moderate to Large Impact:

It is likely that one or more moderate to large impacts could occur under one or more of these circumstances:

  • When land uses with high percentages of the lot are covered in impervious surfaces.
  • Where stormwater generated on site will impact water bodies off-site on other properties.
  • With projects that generate large amounts of stormwater that need engineered stormwater control devices.

e. The proposed action may change flood water flows that contribute to flooding.

Similar to Question 5.d., any project that alters or increases surface water runoff has the potential to contribute to flooding, both on-site and at downstream, upstream, or across stream locations. In addition to channeling, creation of impoundments, or increased or altered stormwater runoff, activities such as removal of stream-side vegetation, changes to riverine wetlands, or changes to stream and river banks can also contribute to flooding. Inadequately sized culverts or bridges can also clog and impede the passage of flood waters. Review the answers and analysis of Part 2, Question 5 (a, b and c) to understand any flooding issues.

Applicable Part 1 Information

D.1.h., D.2.b., D.2.e., E.2.e., E.2.h., E.2.i., E.2.j., and E.2.k.

Analysis

  • Are there any streams, rivers, lakes and any designated floodplains on the project site or nearby that could be influenced by the project?
  • Is any stream side vegetation being removed?
  • Will any changes to drainage ditches or existing channels occur?
  • Are any wetlands being impacted that could change water flow downstream?
  • Is the project impacting any regulated floodplain (see question 5 a, b, and c)?
  • Where will surface water flow from the project site and will it affect off-site streams, rivers or lakes?

Will there be an impact?

If the proposed project does not change floodwater flows to on-site or off-site streams, rivers and lakes, then there will be no related impact. Check 'No, or small impact may occur."

Small Impact:

Proposed projects that include minor changes to the flow patterns but that do not direct large volumes of water into different locations are likely to have only a small impact. Examples would be:

  • Construction of any structure in a 100 year or 500 year floodplain but it is built above base flood pursuant to floodplain management regulations.
  • Land uses that are maintaining or increasing pervious surfaces.
  • Land uses that do not change the flow of water or drainage patterns off site or into surface water bodies that have not received that volume of stormwater before.
  • Minor clearing or grading activities.
Moderate to Large Impact:

Moderate to large impacts could occur under one or more of these circumstances:

  • Construction of large expanses of impervious surfaces within the floodplain.
  • Clearing or grading, creation of walls or berms that alter the flow of water or drainage patterns.
  • Alterations to surface water bodies within a designated floodplain in a manner which alters flow or drainage patterns.

f. If there is a dam located on the site of the proposed action, the dam has failed to meet one or more safety criteria on its most recent inspection.

water cascading down an opening of a dam

Dam failure can do great damage to people, property, and natural habitats downstream, potentially including loss of life.

Dams in the state's inventory of dams are classified according to potential for downstream damage upon dam failure, called Hazard Classification. The safety standards for a dam depend on its hazard classification, with higher hazard dams having to meet more robust criteria. Development within the dam's potential failure inundation area can cause an increase of the dam's Hazard Classification, and put the dam owner out of compliance. A project that contributes more runoff to a dam's impoundment can lead to exceeding the dam's design, and challenge the dam's ability to safely pass flood flows, potentially causing dam failure. High and Intermediate Hazard dam owners are required to have certain documents and submit some of them to the DEC. This includes an Emergency Action Plan

Applicable Part 1 Information

D.1.h., and E.1.e.

Analysis

  • If the dam is in the state's inventory of dams, what is its current Hazard Class?
  • Has there been a recent inspection of the dam?
  • If the dam is a Class C (High Hazard) or Class B (Intermediate), does the owner have an emergency action plan and other required documents?

Will there be an impact?

If there is no dam on the project site, and none is proposed, there will be no related impacts. If a dam is present or proposed that is classified as Hazard Class A and is in compliance, and no part of the project will be downstream of the dam, there would likely be a no impact. Check 'No, or small impact may occur."

Small Impact:
  • If there is a dam on the project site, and it is proposed to be repaired or upgraded, and no part of the project will be downstream of the dam, there will be a small impact.
Moderate to Large Impact:
  • If a dam is present or proposed that is classified as a Hazard Class B or Class C, or if it currently is Class A but parts of the project will be built downstream of the dam such that its hazard class could be raised and the dam will have to be upgraded, there would be a moderate to large impact.

g. Other impacts:

There may be other impacts identified by the reviewing agency that are not addressed by the above questions. If so, they should be identified and briefly described here.

Some proposed actions may have beneficial impacts on the environment. The reviewing agency can use the 'other' category for that purpose, too.

Back to Part 2 (FEAF) Identification of Potential Project Impacts || Continue to Part 2 (FEAF) Question 6 Impacts on Air


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