chapter 26 pop-land changes

Chapter 26
Population Growth, Land Cover Changes and Water
Quality

26.1 Introduction

Human activities can negatively impact surface water quality, even when the activity is far
removed from the waterbody. Pollutants that enter waters fall into two general categories: point
sources and nonpoint sources. With increased population comes increased demand for
wastewater discharge and conversion of land from lower impact uses to more intensive urban
and suburban land uses. In the Cape Fear River basin, there are over 300 miles of Impaired
streams that drain urban or urbanizing areas. With proper management of wastes and land use
activities, these impacts can be minimized. Every person living in or visiting a watershed
impacts water quality. Therefore, each individual should be aware of these contributions and
take actions to reduce them. This chapter provides an overview of population growth impacts
associated with increased wastewater discharges and conversion of land from agriculture and
forestry to urban land uses.

The Cape Fear River basin is one of the fastest developing basins in the state; the effects of
development are impacting water quality. Population in the Cape Fear River basin has grown
from just under 1.5 million to over 1.8 million people from 1990 to 2000. The overall population
of the basin based on 2000 Census data is 1,834,545, with approximately 197 persons/square
mile. This growth is expected to continue especially around existing urban areas. The 26
counties with some land area in the Cape Fear River basin are expected to increase population
from just under 3 million to over 5 million people (28.9 percent) over the next 20 years
(Appendix I). Associated with this growth will be increasing strain on water resources for
drinking water, wastewater assimilation and runoff impacts. There will also be loss of natural
areas and increases in impervious surfaces associated with construction of new homes and
businesses.

26.2 Impacts of Increased Wastewater Discharges

Point sources are typically piped discharges and are controlled through regulatory programs
administered by the state. All regulated point source discharges in North Carolina must apply for
and obtain a National Pollutant Discharge
Elimination System (NPDES) permit from
the state. There has been an increase in
wastewater flow discharged to waters in
the Cape Fear River basin to meet the
demands of the rapidly growing
population. Generally, treatment
technology has improved to the extent that
point sources are no longer the primary
source of water quality problems.
Point Sources

Piped discharges from:
• Municipal wastewater treatment plants
• Industrial facilities
• Small package treatment plants
• Large urban and industrial stormwater systems

Chapter 26 – Population Growth, Land Cover Changes and Water Quality 246

In the Cape Fear River basin, there are just over 150 Impaired stream miles where point sources
are a possible contributor to water quality problems. There are just over 340 miles of streams
that may have been adversely impacted by discharges. Most of these streams are located in
urban areas where water quality is already degraded. Because of limited assimilative capacity in
the basin local governments, industry and the state must carefully plan for wastewater increases
on a basinwide scale. Chapter 30 discusses NPDES compliance issues and permitting strategies
to be used to accommodate new and expanding discharges in this basin.

26.3 Impacts of Growth and Development

Nonpoint sources are from a broad range of land use activities. Nonpoint source pollutants are
typically carried to surface waters by rainfall, runoff or snowmelt. Sediment and nutrients are
most often associated with nonpoint source
pollution. Other pollutants associated with
nonpoint source pollution include fecal coliform
bacteria, heavy metals, oil and grease, and any
other substance that may be washed off the
ground or deposited from the atmosphere into
surface waters.
Nonpoint Sources

• Construction activities
• Roads, parking lots and rooftops
• Agriculture
• Failing septic systems and straight pipes
• Timber harvesting
Unlike point source pollution, nonpoint pollution
sources are diffuse in nature and occur
intermittently, depending on rainfall events and
land disturbance. Given these characteristics, it is difficult and resource intensive to quantify
nonpoint contributions to water quality degradation in a given watershed. While nonpoint source
pollution control often relies on voluntary actions, the state has many programs designed to
reduce nonpoint source pollution.
• Hydrologic modifications
Cumulative Effects Water quality issues and programs associated with
agricultural are discussed in Chapter 28. Water quality
issues and programs associated with forestry are
discussed in Chapter 29. The remainder of this chapter
will discuss water quality issues associated with
conversion of land to urban and suburban areas.

While any one activity may not have a
dramatic effect on water quality, the
cumulative effect of land use activities
in a watershed can have a severe and
long-lasting impact.

Urban land uses have increased from 370,000 acres in 1982 to 627,000 acres in 1997 (70
percent) in the Cape Fear River basin (Appendix III). At this rate of development, well over 1
million acres will be in urban land cover by 2020. Water quality declines dramatically in
streams in and around urban centers and along interstate corridors. Most of the Impaired streams
in this basin are concentrated in and around existing urban areas. In the Cape Fear River basin,
over 300 Impaired stream miles are associated with urban and urbanizing areas. Programs in
place to help prevent further degradation to water quality during development are discussed in
Chapter 31.

More than any other human activity, urban growth is the greatest threat to aquatic resources. The
impacts on rivers, lakes and streams, as development surrounding metropolitan areas consumes
neighboring forests and fields, can be significant and permanent if stormwater runoff is not
Chapter 26 – Population Growth, Land Cover Changes and Water Quality 247

controlled. Greater numbers of homes, stores and businesses require greater quantities of water.
Growing populations not only require more water, but they also lead to the discharge and runoff
of greater quantities of waste and pollutants into the state’s streams and groundwater. Thus, just
as demand and use increases, some of the potential water supply is lost (Orr and Stuart, 2000).

In addition, as watershed vegetation is replaced with impervious surfaces in the form of paved
roads, buildings, parking lots, and residential homes and driveways, the ability of the
environment to absorb and diffuse the effects of natural rainfall is diminished. Urbanization
results in increased surface runoff and correspondingly earlier and higher peak streamflows after
rainfall. Flooding frequency is also increased. These effects are compounded when small
streams are channelized (straightened) or piped and storm sewer systems are installed to increase
transport of drainage waters downstream. Bank scour from these frequent high flow events tends
to enlarge urban streams and increase suspended sediment. Scouring also destroys the variety of
habitat in streams, leading to degradation of benthic macroinvertebrate populations and loss of
fisheries (EPA, 1999).
Water supply needs have normally been sufficient to meet agriculture, water supply, industrial
and power generation needs. The severe drought conditions in 2001 and 2002 stressed water
resources to near the limit for these uses. It is during these periods of drought that point to the
impending threats to the availability of good quality water. Clean water can likely be provided
in sufficient quantity to supply the future needs of the basin, but only with inspired foresight,
planning and management. Refer to Chapter 32 for more information on water resources
management.

Most of the impacts result in habitat degradation (Chapter 27), but urban runoff also carries a
potentially toxic cocktail including oil and grease from roads and parking lots, street litter and
pollutants from the atmosphere. Cumulative impacts from developing and urban areas can cause
severe impairment to urban streams.

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