Impacts of Urbanization on Waterways · Impacts of Urbanization on Waterways 1 Impacts of Urbanization on Waterways Cooperative Extension Bringing the University to You Audiovisual-05-14

Impacts of Urbanization on Waterways 1

Impacts of Impacts of Urbanization on Urbanization on

WaterwaysWaterways

Cooperative ExtensionBringing the University to You

Audiovisual-05-14

S. Donaldson

Impacts of Urbanization on Waterways

Susan DonaldsonMelody HefnerUniversity of Nevada Cooperative Extension Audiovisual-05-14

Healthy streams are essential for protecting water quality. They also add to the quality of life in our area, providing recreational opportunities such as fishing and swimming, and an attractive element of green in the parched desert. As our community grows, it becomes increasingly important to safeguard our streams by planning ahead to avoid impacts.

Portions of this presentation were adapted from The Impacts of Urbanization, Center for Watershed Protection, 1999.


NNonpoint onpoint EEducation for ducation for MMunicipal unicipal OOfficialsfficials

NEMONEMO is an educational program for is an educational program for land use decision makers addressing the land use decision makers addressing the relationship between land use and water relationship between land use and water

resource protection.resource protection.

NEMO stands for “Nonpoint Education for Municipal Officials.”


Water movement (hydrology)Water movement (hydrology)Stream channel shape and Stream channel shape and function (fluvial geomorphology)function (fluvial geomorphology)Water qualityWater qualityHabitat Habitat

The effects of urbanization on The effects of urbanization on water resources can be water resources can be organized into four categories:organized into four categories:

This presentation will examine four categories of impacts to our water resources.


How does urbanization affect How does urbanization affect stream hydrology?stream hydrology?

Disrupts natural Disrupts natural water balancewater balanceIncreases Increases flood peaksflood peaks, storm water , storm water runoff, and bankfull flowsrunoff, and bankfull flowsMore frequent floodingMore frequent floodingLower Lower baseflowbaseflow to streams to streams (less water in the stream)(less water in the stream)

One of the major impacts of urbanization on streams is the effect on stream hydrology. Stream hydrology is defined as the study of the movement or flow of water in streams. Understanding water movement is essential to understanding the impact of development on urban streams.


•Greater infiltration •Greater uptake by plants

•Reduced infiltration •Reduced uptake by plants•Increased surface runoff

Center for Watershed Protection

Water balance is a measure of the amount of water entering and leaving a system. As rain falls to earth, some of it is infiltrated, absorbed, and evapotranspired, and some becomes runoff. As you learned earlier, in a pre-developed setting, much of the rainfall is absorbed by the surrounding vegetation, soil and ground cover. This diagram shows how development and its corresponding increase in impervious cover disrupts the natural water balance. In the post-development setting, the amount of water running off the site is dramatically increased and the amount of water infiltration is decreased. The changes in the water balance in urban streams are exemplified by changes in the volume of runoff, increased flood peaks, increased and earlier peak flows and frequency of bankfull flows, floodplain widening, and decreased dry weather flows.


Catch basins or inlets collect

storm water and direct it through

pipes to a downstream storm water detention/

retention facility or to the

receiving waters.

Curbs and gutters are designed to

deliver storm water away from the road surface

in an efficient and timely manner.

Photos Copyright 1999, Center for Watershed Protection

Flooding occurs when there are excessive runoff volumes. These excessive volumes are caused by both the total amount of impervious cover as well as the rate at which the runoff is delivered to the stream. Curbs and gutters, storm drains, storm drain pipes, ditches, catch basins and other drainage systems quickly speed the runoff to a storm water detention/retention facility or directly into the nearest water body. Curbs and gutters are designed to deliver storm water away from the road surface in an efficient and timely manner.Catch basins or inlets collect storm water and direct it through pipes to a downstream storm water detention/retention facility or to the nearest water body.


Often, the runoff is directly

discharged into nearby water

bodies without any treatment.

Photo Copyright 1999, Center for Watershed Protection

And as you now know, most of our local storm drains deliver storm water to the nearest water body without treatment.


The large amount of runoff

entering an urban stream can frequently

result in flooding, such as

this moderate overbank

flooding event.

S. Donaldson

This picture was taken one week after the January 1997 flood peak. Note that Steamboat Creek in Pleasant Valley is still flowing over its banks due to releases of water from Little Washoe Lake.



This slide illustrates the effect of urbanization on hydrograph peak discharge. A hydrograph is a graph showing the changes in streamflow with respect to time. During storms, in pre-developed “natural” conditions (the solid line), the stream flow gradually increases to a relatively flat, prolonged peak that is about twice the pre-storm flow rate, and gradually descends to a low-flow condition (“gradual recession”). During storms, in the urbanized condition (dashed line), the flow rapidly increases to a peak that occurs earlier in time due to the rapid delivery of water from storm drains and pavement. You’ll notice that the peak flows are much higher than occurred prior to development (more than double) which means that flows in the stream will be much higher than occurred previously, and flooding may increase. The flow then sharply decreases, often to a low-flow condition that is lower than occurred prior to development. This means that during dry periods, the flow in streams is decreased and impacts to water users or aquatic habitat may occur.


Bankfull flooding (or the condition of the flow that

"fills up" the channel) occurs

much more frequently in

highly urbanized areas and has the potential to be extremely erosive and

damaging to the natural form and function of the

stream.


In addition to the increase in flood peaks and peak discharge, the frequency of bankfull flows also increases with increased urbanization. Bankfull flows are simply runoff events that fill the normal channel of a stream to the top of the banks. Bankfull flows are significant because they are the channel-forming flows in streams, and they are highly erosive, turbid, and damaging to the natural morphology of the stream.


Floodplain After Filling

ASFPM

Development within the floodplain area also changes the fluvial geomorphology, or stream form and function. Not only is the volume of runoff increased due to less infiltration resulting from increases in impervious surfaces, space in the floodplain is now occupied by fill and buildings. This causes the floodplain height to rise, potentially damaging adjacent buildings that once were considered “safe” during floods. This effect was seen during the 1997 flood in the Sparks industrial area.


Decline in Decline in streamflowstreamflow due to diminished due to diminished groundwater rechargegroundwater recharge

An increase in impervious surface often decreases the amount of rainfall available for infiltration. Without infiltration, the groundwater will not be recharged and the stream will

lose this potential source of water. Thus low flows tend to be lower in urbanized watersheds.


The hydrologic impact of urbanization is not limited to storm events. During dry weather periods, urban streams tend to have less flow because groundwater recharge from storm water infiltration has been diminished. While streams that have never been developed retain their flow during dry weather conditions, many urban streams lack the baseflow (flow contributed by groundwater) necessary to sustain healthy habitat conditions during extended periods of dry weather.


Summary: Hydrologic EffectSummary: Hydrologic Effect

Disrupted natural Disrupted natural water balancewater balanceIncreased Increased flood peaksflood peaks, storm water , storm water runoff, and bankfull flowsrunoff, and bankfull flowsMore frequent floodingMore frequent floodingLower baseflow to streams (less Lower baseflow to streams (less water in the stream)water in the stream)

The changes in hydrology may have unexpected impacts to the surrounding land. As water tables drop, plants that depend on certain levels of soil moisture may die. This changes the plant community, dries the soils, and has the potential for increasing soil erosion and wind-borne dust.


How does urbanization affect the How does urbanization affect the stream form and function?stream form and function?

Stream widening & erosionStream widening & erosionReduced fish passageReduced fish passageDegradation of habitat structureDegradation of habitat structureDecreased channel stabilityDecreased channel stabilityLoss of poolLoss of pool--riffle structure needed riffle structure needed by fishby fish

Fluvial geomorphologic changes, or changes in the shape, function, and composition of streams, occur along with hydrologic changes as urbanization increases.


Functioning channel

Downcutting and bank erosion have occurred.

Stream is very wide and shallow. This stream is not functioning.

UNCE

This diagram shows the progression of stream channel degradation.

Many functioning channels are narrow and deep, with overhanging banks. Vegetation shades the water surface, keeping temperatures cool. Stored ground water sustains grass, shrub, and/or tree communities. The riparian resources of vegetation, water, and soil are working together.Once downcutting and bank erosion have occurred, the stream becomes wider and the water table drops. As the stream becomes wider and shallower, the water gets hotter in the summer. In cold climates it may begin to freeze solid in the winter. Both are problems for cool-water fish and other species. The water no longer spills out onto the floodplain on a regular basis. Because water is no longer freely available on the old floodplain, water-loving vegetation on the new stream terrace dies. This further weakens the streambanks. As the riparian area loses its vegetation, erosion increases, and the channel becomes very wide and very shallow before it creates a new floodplain down along the sides of the channel. Water-loving vegetation may begin to grow on the new floodplain in the bottom of the channel. The stream, if left alone, will slowly begin to heal itself in a new form with a new floodplain in the bottom of the incised channel.Too many streams have already experienced some level of degradation. Fortunately, many that incised long ago are beginning the process of healing via increased width, floodplain development, and riparian vegetation.


In watersheds with less than 5

percent impervious

cover, streams are typically stable and pristine.


Following are some examples of streams in watersheds with varying amounts of impervious cover.

An undeveloped watershed with less than 5 percent impervious cover is characterized by excellent streams conditions - good riparian cover, high quality substrate, and wetted perimeter during low flow conditions.


While this stream at 8-10

percent impervious cover is still relatively stable, signs of stream erosion

are more apparent.


While this stream at 8-10 percent impervious cover is still relatively stable, signs ofstream erosion are more apparent and include loss of the wetted perimeter, more eroded material in the banks, and debris.

Generally, most urban streams begin to enlarge as impervious cover exceeds 10 percent in the watershed. This finding has been discovered in various places like Puget Sound, Washington; Austin, Texas; and Vermont. The enlargement process may take up to 50 years to fully occur, but urban streams with more than 10 percent impervious cover are characterized by various degrees of stream enlargement and widening, erosion, downcutting, decreased channel stability, and embeddedness.


The surrounding area of this stream is

approximately 20 percent

impervious cover and the stream exhibits much

more bank erosion.


Note the vertical banks with eroded material at their base. The absence of a vigorous root structure provides little protection from erosion as flows increase.


This stream has a surrounding area of approximately 30 percent

impervious cover.


This stream has a surrounding area of approximately 30 percent impervious cover. The large amount of impervious cover has increased the size of the stream by a factor of five to ten. The manhole in the middle of the picture was originally in the floodplain and is an indicator of the degree to which channel erosion has occurred.


The stream pictured here has downcut several feet in elevation because of the increased storm water flow. In this case, the forested wetland in the floodplain is now hydraulically disconnected from the stream that sustained it.


Not only can a stream widen, but given the right soil conditions, it can cut down (or incise) as well. In this slide, the stream has dropped several feet in elevation because of increased storm water flows. The forested wetland in the floodplain is now hydraulically disconnected from the stream that sustained it. These trees will likely die due to lack of water.


In many highly urbanized areas, natural streams have been

channelized to speed runoff along, but these fail to provide any habitat

value.


When impervious cover exceeds 40 percent, engineers are often called in to channelize or stabilize stream channels. In the past, concrete channels were used to speed runoff further along, but there is no habitat value to these engineered channels.


How does urbanization affect How does urbanization affect water quality?water quality?

Increased stream temperature Increased stream temperature (thermal stress)(thermal stress)Increased pollutantsIncreased pollutantsIncreased risk of fishing Increased risk of fishing advisories/beach closuresadvisories/beach closuresIncrease in costs!Increase in costs!

In addition to hydrologic and geomorphologic changes to the stream, urbanization directly impacts the quality of the receiving water. Some of the indicators of the impact of urbanization on water quality include increased stream temperature and pollutants.


Urbanization causes the

temperature of streams to rise, both during low flow and storm

events.


Stream temperature is a very important habitat parameter for salmon, trout, and other fish and insects. Temperature variability can dictate the growth of aquatic insects and timing of migration and molts. Impervious cover increases air and soil temperatures and can create an increase of 5 to 10 degrees Fahrenheit in urban streams.


S. Donaldson

An increase in pollutants can adversely affect aquatic organisms and can result in beach closure, safety concerns, and/or activity limitations for people. High levels of bacteria can create unsafe conditions, leading to warnings and use restrictions.


C. Conway

Another common pollutant in urban storm water is sediment. Sediment can smother bottom organisms or it can clog gills of fish and aquatic insects when it is in the water column. Sources of sediment include streambank erosion, construction sites, and the runoff from paved surfaces. This picture shows sediment entering the Truckee River from the North Truckee Drain on an average day. Greater amounts enter the Truckee River after rainstorms.


Effects of urbanization on habitatEffects of urbanization on habitatLoss of buffer zonesLoss of buffer zonesLoss of Loss of large woody debrislarge woody debrisCreation of fish barriersCreation of fish barriersDecline in habitat value of streamsDecline in habitat value of streams

Decline in habitat quality for all wildlifeDecline in habitat quality for all wildlifeDecline in plant and animal diversityDecline in plant and animal diversityDecline in reproduction and loss of plants Decline in reproduction and loss of plants and animals species and animals species

Consequences of habitat declineConsequences of habitat decline

Along with changes in hydrology, geomorphology, and water quality, the habitat value of urban streams diminishes with increased impervious cover. There are numerous impacts to the aquatic habitat as well as the streamside (riparian) zone.



Here the banks of the stream are lined with grass, which provides some protection

for the streambank but

lacks the stability,

shading, and habitat benefits that trees can

provide.

S. Donaldson

All vegetation is not equal! Trees are useful for providing stability, shade, and habitat benefits. This stream, while it is well-vegetated with grass and has good floodplain access, could have been planted with a variety of types of vegetation to improve habitat. Also, the intensive use of turf grass is likely associated with fertilizer and pesticide inputs.


Culverts and dams such as

this act as barriers to fish migration and

cut off spawning areas.

worldpoto.com

The creation of fish barriers is another impact of urban development. Culverts and dams like this one at Marble Bluff act as barriers to fish migration unless they are carefully designed. Barriers can prevent the movement of both anadramous(migrating) and resident fish. In some cases, the fish barriers are created by culverts that are put in stream crossings for roads and other urban infrastructure. As the stream erodes down, vertical barriers to fish movement are created that cut off spawning areas. In many areas of the West Coast, where salmon spawn, fish barriers are a major biological problem associated with urban development.



In this urban stream, habitat structure is lost

and flows are more shallow,

slow-moving and indistinct.

S. Donaldson

In an enlarged urban stream, habitat structure is lost and flows become more shallow, slow moving and indistinct. The channel enlargement process sharply degrades stream habitat structure and flows become more shallow, slow-moving and indistinct. High-quality streams have a series of pools, riffles, and glides thatprovide unique and stable habitat areas for different fish and aquatic insects. Urban streams are characterized by highly scattered and poor-quality stream beds.


This wide stream with huge sediment

deposits, no forest canopy, and likely poor

aquatic community is classified as

non-supporting.


Much of the biological diversity and many of the human uses of impacted streams can be protected and restored through proper watershed management. If degradation proceeds to the non-supporting classification, restoration becomes much more difficult. Non-supporting streams can no longer support a diverse stream community and water contact recreation is no longer possible due to high bacteria levels.


What makes a “healthy”stream?

S. Donaldson

A well-functioning or “healthy” stream:•Has clean, clear water•Has vegetation on its banks to knit soil together and reduce erosion•Aids in flood retention and recharge•Can handle typical sediment loads•Provides habitat and supports greater biodiversity

The official definition is provided below:Proper functioning condition (PFC): Riparian-wetland areas are functioning properly when adequate vegetation, landform, or large woody debris is present to dissipate stream energy associated with high waterflows, thereby reducing erosion and improving water quality; filter sediment, capture bedload, and aid floodplain development; improve flood-water retention and groundwater recharge; develop root masses that stabilize streambanks against cutting action; develop diverse ponding, and channel characteristics to provide the habitat and the water depth, duration, and temperature necessary for fish production, waterfowl breeding, and other uses; and support greater biodiversity. The functioning condition of riparian-wetland areas is a result of interaction among geology, soil, water, and vegetation.


S. Donaldson

This local creek (Galena) has some of the attributes of a healthy stream. Note the variety of riparian vegetation shading the stream. The stream itself is relatively narrow, but has room to spread out onto the floodplain. There are no obvious signs of major erosion. The water is clear and cool, and supports trout.


S. Donaldson

Steamboat Creek near the Truckee River is very different from Galena Creek. Notice the steep, vertical, eroded banks; the widened channel; the lack of vegetation other than noxious weeds (tall whitetop); the murky water; and the lack of a floodplain. This creek is the largest source of NPS pollution to the Truckee River.


Photo Copyright 1999, Center for Watershed ProtectionS. Donaldson

Efforts are underway to restore a number of local creeks. Here, Dry Creek has been routed into a low-flow channel with good floodplain access. However, work remains to be done to establish a diverse, desirable plant community. Currently, many of the plants are noxious weeds or undesirable species such as stinging nettles. There is no shade to cool the water.


Knowledge of the amount of

impervious cover in a watershed

can help managers

assess the most effective

techniques for managing streams.


Why is there so much emphasis on stream condition? Stream condition directly affects water quality. It’s not always easy to predict whether there will be impacts to waterways from development, however. Impervious cover estimates can help us determine the impacts we should expect to experience, and some strategies for coping.


Impervious surfaces vs. runoffImpervious surfaces vs. runoff

Increased:Increased:Runoff speedRunoff speedBankfull flowsBankfull flowsPeak flowsPeak flowsVolumeVolumeFlood heightsFlood heights

Decreased:Decreased:InfiltrationInfiltrationBaseflowBaseflowGroundwater Groundwater rechargerechargePollutant filtrationPollutant filtrationRunoff qualityRunoff quality

This slide summarizes what we’ve learned about the effects of impervious surfaces on runoff quantity and quality.


ADAPTED FROM SCHUELER, ET. AL., 1992ADAPTED FROM SCHUELER, ET. AL., 1992

8080

7070

6060

5050

4040

3030

2020

1010

00STREAM DEGRADATIONSTREAM DEGRADATION

WA

TER

SHED

IMPE

RVI

OU

SNES

SW

ATE

RSH

ED IM

PER

VIO

USN

ESS

( per

cent

)( p

erce

nt)

DEGRADED

PROTECTED

IMPACTED

Relationship between impervious Relationship between impervious cover and streamcover and stream qualityquality

A simple model to classify and manage urban streams can be constructed based on impervious cover. The model helps determine the impacts of impervious cover based on three stream categories: sensitive, impacted, and non-supporting. When impervious cover is less than 10 percent, we still can maintain a high quality stream system that maintains stable banks, has high fish diversity and good water quality. Once impervious cover exceeds 10 percent, the pristine conditions of the sensitive stream cannot be maintained. Impacted streams characterized by 10 percent and 25 percent impervious cover begin to show varying degrees of influence from land development, including unstable channels, declining water quality, and diminished biological communities. Non-supporting or degraded streams exceed 25 to 30 percent impervious cover and are characterized as highly unstable, have poor fish and aquatic insect diversity, and very poor water quality. Certain measures can be taken to reduce impacts, but water quality is still going to suffer some level of degradation in these developed watershed.

Urban Stream Classification ModelImpervious cover <10 percent = sensitive or protectedImpervious cover 10-25 percent = impactedImpervious cover >25 percent = degraded to non-supporting


Las Vegas, Las Vegas, 19731973

USGS

We hear a lot about incredible growth rates in the Las Vegas Area. These images are from a USGS circular. This first one shows development in Las Vegas in 1973.The images used in this circular were generated from land cover data developed by the USGS. The data sources include the Geographic Information Retrieval and Analysis System (GIRAS) for the 1970s images and the National Land Cover Dataset (NLCD) for the 1990s images. The images were developed using a geographic information system (GIS). In the final images, all urban areas are shown in red. A shaded-relief map of each region was used to display the topographic context of the red polygon coverage. For all of these images, urban land is defined as areas transformed into a built-up environment for human use. It includes residential areas, commercial and industrial developments, transportation features, and institutions.This image is from USGS circular 1282, Urban Growth in American Cities Glimpses of U.S. Urbanization, Roger Auch, Janis Taylor, and William Acevedo, January 2004.


Las Vegas, Las Vegas, 19921992

USGS

This second Las Vegas image shows substantially increased amounts of development in Las Vegas as of 1992.

This image is from USGS circular 1282, Urban Growth in American Cities Glimpses of U.S. Urbanization, Roger Auch, Janis Taylor, and William Acevedo, January 2004.


Reno, 1973

USGS

But Las Vegas is not the only area in Nevada experiencing significant growth. This map shows the Truckee Meadows area in 1973.



Reno 1992Reno 1992

USGS

This graphic shows the spread of development in the Truckee Meadows as of 1992.



Where do we go Where do we go from here?from here?

NRCS photo gallery

We’re faced with evidence daily that growth has steadily increased since 1992 in the Truckee Meadows. Growth is a fact of life, but we must ensure that our development plans and methods work towards decreasing runoff, promoting infiltration, and protecting waterways. This will help us meet our ultimate goal -protecting water quality.

Documents

Impacts of Urbanization on Waterways · Impacts of Urbanization on Waterways 1 Impacts of Urbanization on Waterways Cooperative Extension Bringing the University to You Audiovisual-05-14