percent developed imperviousness within the fayetteville arkansas planning area

The City of Fayetteville Planning Area Percent Developed Imperviousness

The effective management and regulation of urban runoff can help reduce the potential for property damage, environmental harm or personal injury do to the impacts of major flooding events. Runoff is the flow of water that occurs when excess stormwater flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more quickly than soil can absorb it, or because impervious areas (roofs, pavement, etc.) send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion and other forms of nonpoint source pollution that can contaminate drinking water. (Source: https://en.wikipedia.org/wiki/Surface_Runoff) __________________________ The City of Fayetteville enforces several regulations designed to mitigate the adverse impacts of runoff including: •  The Fayetteville Drainage Criteria Manual. •  The Stormwater Management, Drainage, and

Erosion Control Ordinance. •  ADEQ NPDES Construction Stormwater General

Permit. •  U.S. Army Corps of Engineers Section 404 of the

Clean Water Act . •  Floodplain Development Permits •  Ordinances including; The City 2030 Plan and

Zoning Regulations.

Source: https://www.fayettevilleflyer.com

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The Fayetteville Drainage Criteria Manual outlines the minimum

stormwater standards including the following equations for estimating runoff:

- The Rational Formula, Q=ICA

- The SCS TR-55/TR-20 Formula, Q=(P-0.2S)2/(P+0.8S)

where S=(1000/CN)-10

Percent Imperviousness represents one of the major physical characteristic affecting surface runoff and has been incorporated through coefficient calculations in the equations above for estimating runoff. Other physical characteristics affecting runoff include:

•  Land Cover/Use •  Soil type (infiltration rate) •  Slope •  Drainage area •  Basin shape

Meteorological factors affecting runoff include:

•  Type of precipitation •  Rainfall intensity •  Rainfall amount •  Rainfall duration •  Distribution of rainfall

Source: http://water.usgs.gov/edu/runoff.html

Source: http://firstarkansasnews.net/2011/04/flood-photos

City of Fayetteville Planning Area Percent Developed Imperviousness

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The greater the amount of impervious surfaces the greater the potential runoff. That is why documenting and tracking the degree, quantity and distribution of this significant variable is useful to help quantify the potential magnitude of surface runoff that may

result from major rain events.

Study Objectives: •  Identify a regularly updated, consistently

produced, quality source of derived percent developed imperviousness data.

•  Utilize this data to document the distribution and general characteristics of percent developed imperviousness within the City of Fayetteville Planning Area.

•  Propose adopting “percent developed imperviousness” metrics to help monitor progress in reaching selected 2030 Plan goals and managing runoff potential within the Fayetteville Planning Area.

•  Propose adopting “percent developed imperviousness” metrics to help monitor progress in reaching a 2030 Plan goal, manage conservation activities and document runoff potential within the Enduring Green Network.

Geospa*al Model


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The study utilizes 2001, 2006 and

2011 input raster's that are derived products from the National

Land Cover Database

Data Product Advantages: •  The National Land Cover Database (NLCD) serves

as the definitive Landsat-based, 30-meter resolution, land cover database for the Nation.

•  NLCD provides spatial reference and descriptive data for characteristics of the land surface, percent impervious surface, and percent tree canopy cover.

•  NLCD products are created by the Multi-Resolution Land Characteristics (MRLC) Consortium, a partnership of Federal agencies led by the U.S. Geological Survey.

•  NLCD data products are available for download at no charge to the public from the MRLC Web site: http://www.mrlc.gov.

•  NLCD land cover products are directly comparable products to enable a wide spectrum of change analysis by users.

•  NLCD conducts formal accuracy assessments to provide users feedback on product accuracy.

•  The NLCD Imperviousness product is scheduled to be updated regularly on a five year cycle.


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Source: Derived from NLCD Percent Developed Imperviousness, MRLC GIS: ESRI ArcMAP 10.4.1

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Source: Derived from NLCD 2001 Percent Developed Imperviousness, MRLC: GIS: ESRI ArcMAP 10.4.1


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Suggested Percent Developed Imperviousness Metrics •  Mean % Imperviousness – This metric represents the average of all the cell values (0 to

100%) within the Fayetteville Planning Area for an assessment year. This is a good index of the overall runoff potential within the Planning Area.

•  Mean >0 % Imperviousness – This metric represents the average of all the cell values

within the Fayetteville Planning Area that have undergone some level of impervious development. This is a good index for the overall intensity or magnitude of impervious development within the Planning Area.

•  % of Area with Cell Values >0 – This metric represents the total number of cells with

percent imperviousness values greater than zero divided by the total number of cells in the Planning Area. This metric is a good index of the spatial extent of impervious development with in the Planning Area.

•  The Fayetteville Planning Area is used as the geographic extent for calculating the metrics

because it represents the City’s potential growth area, the City has some level of control over the area and the boundaries do not change as frequently as the city limits.

•  Population is used to project metric values over time.

Faye5eville Planning Area 2001 2006 2011 2016p 2021p 2026p 2031p 2036p

Mean % Imp 7.70 9.05 9.95 10.40 11.95 13.45 15.03 16.93 >0 % Imp Mean 27.94 29.99 31.09 36.30 39.12 41.85 44.72 48.17 Cells >0 % Imp 71932 78767 83538 88973 97319 105400 113908 124128 % of Plan Area 27.57 30.19 32.02 34.11 37.31 40.40 43.66 47.58 Popula*on 69759 79202 88994 97827 111921 125565 139932 157189

p Projected (Source: h5p://www.faye5eville-‐ar.gov/DocumentCenter/Home/View/1220)

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Establishing metrics like the three proposed above offer advantages for the City of Fayetteville to monitor its efforts to manage runoff. The Mean % Imperviousness metric allows the City to track a general, but, meaningful runoff variable over time. The fact that it is a simple calculation performed on data supplied by a reputable third party is important in making the metric highly credible. In addition, the availability of equivalent percent imperviousness values over the entire United States opens up the opportunity to make valid comparisons of runoff conditions over large geographical areas (i.e. counties, region, watersheds, etc.) resulting in policy opportunities a several levels. Finally, the spatial nature of a 30 meter raster providing values of imperviousness (0 to 100%) allows the City to document its distribution and investigate its relationship with other spatial data while preserving an important degree of anonymity. The Mean >0 % Imperviousness and % of Area with Cell Values >0 offer the same advantages outlined above while allowing the City to focus on understanding the geographic nature and intensity of imperviousness in areas being impacted by the encroachment of urban development. In addition, the three metrics discussed above can help the City monitor and manage it’s efforts to accomplish thee of the City’s 2030 Plan Goals:

•  Make appropriate infill and revitalization our highest priorities. •  Discourage suburban sprawl. •  Make traditional town form the standard.

As an example, if the City is experiencing year over year increases in the first two metrics, but is able to hold the line on the third metric, it would suggest that progress has been made towards the accomplishment of all thee goals.

City of Fayetteville Planning Area Percent Developed Imperviousness 9

Percent Developed Imperviousness in the

Enduring Green Network

There is another important application for the Percent Developed Imperviousness metrics in helping the City monitor and manage the accomplishment of a fourth 2030 Plan Goal:

�  Assemble an Enduring Green Network (EGN) The 2030 Plan defines the Enduring Green Network as a A linear park, trail corridor, or open space conservation area that provides passive recreational opportunities, alternative transportation options and the conservation of open space or natural areas. The Plan further defines natural areas as lands approximating or reverting to a wilderness condition, including those with limited development potential due to topography, hydrology, vegetation or value as an environmental resource. These resources can include stream and wildlife corridors, as well as natural hubs and cores, as identified in the Fayetteville Natural Heritage Association study, many of which make up the backbone of the Enduring Green Network.

The City can use percent developed imperviousness metrics as a tool to help manage the Enduring Green Network (EGN) by identifying the aerial extent and intensity of the threat of encroaching development. This type of metric can also be used as an index of the Enduring Green Network’s overall ability to function as a green infrastructure resource that helps reduce the negative impacts of excessive runoff. Mean % Imperviousness and Mean >0 % Imperviousness – These metrics represents the average % imperviousness of all the cell values within the EGN and the average of just cell values greater than zero for an assessment year. In 2011 the first metric value was 4.73 % and the second metric value was 26.4 %. A future increase in these metrics would suggest a progression in the encroachment of urban development in the EGN. And the examination of an updated raster map of percent imperviousness values would show where the encroachment was occurring. % of Area with Cell Values >0 - This metric is the number of raster cells with values greater than zero divided by the total of raster cells comprising the EGN. In 2011 this metric value was 17.9%. An increase in this metric would suggest a progression in the encroachment of urban development on the EGN. A future increase in all three metrics would suggest a reduction in the ability of the EGN to help reduce the negative impacts of excessive runoff.

The map below illustrates the distribution and intensity of areas of low to high percent development imperviousness within the intersection of the boundaries of the Enduring Green Network and Fayetteville Planning Area. The light green polygon is the boundary of the EGN. The red polygon is the boundary of the Planning Area and for reference, the blue polygon is the 2011 city limits. In areas of the EGN outside the Planning Area, the City has the least control over managing the percent development imperviousness within the EGN. Relying primarily on attempts to influence land use policy, conservation and preservation actions taken by the NWARPC, counties or other municipalities. Therefore, this area is not part of the raster data depicted on the map. The map depicts areas within the EGN that have lower percent imperviousness as darker green and areas with higher percent imperviousness as lighter green to white. This information, when combined with other spatial data, can be used by the City to prioritize and direct conservation, preservation and restoration activities within the EGN.

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percent developed imperviousness within the fayetteville arkansas planning area

Environment