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Clean water resources are critical to the health of plant communities, wildlife, and people. It is also important for supporting recreation. Stewardship of waterways and surrounding areas can protect and improve water resources.
Water resources in Pennsylvania include rivers, creeks, runs, ponds, lakes, wetlands (swamps, marshes, fens, bogs, spring seeps, vernalF pools), and groundwater. This section of the Stewardship Handbook focuses on aquatic resources and groundwater; see Wetlands for the rest. Pennsylvania has over 86,000 miles of streams, second only to Alaska among U.S. states. Pennsylvania also contains over 2,500 lakes and 1,500 ponds, covering more than 160,000 acres. Only about 50 of Pennsylvania’s lakes originated naturally, nearly all remnants of glaciation during the last several ice ages in the northwest and northeast parts of the state. Water bodies are vital for aquatic life and as integral parts of food webs in Pennsylvania. They are also valued for drinking water, recreation, and scenic views.
Qualities of healthy rivers, creeks, and runs include stable streambanks, forested riparian buffers, cobble and gravel streambeds, healthy macroinvertebrate populations, and having unimpaired floodplain connectivity (streams are connected to adjacent natural cover in their floodplains, rather than being disconnected through disturbances like levees or channel downcutting, leaving the streams too low to connect to adjacent, higher vegetation). Most streams have a diversity of habitats, including sequences of pools with deeper and slower water, and riffles, faster moving areas that are shallow and often have rocky beds. Healthy streams are free of pollutants from surrounding land uses. Free-flowing streams without dams to hinder upstream passage of fish and other organisms are healthier. These characteristics together help ensure high water quality and good habitat for aquatic life.
Qualities of healthy ponds and lakes include water chemistry below pollution thresholds, a vegetated riparian buffer, minimal to no human disturbance of shorelines, minimal fluctuation of water levels, diversity and abundance of vegetation structure (submerged and emergent species) in shallow areas, and diversity of habitat in the shoreline corridor from shallow water to upland vegetation.
Natural lands directly influence the quality and quantity of water that constitutes the system of streams, ponds, lakes, wetlands, and groundwater in the region. In general, rivers, creeks, and runs and their associated aquatic biota in Pennsylvania developed within forested landscapes. Forest cover moderates streamflow throughout the year by maximizing infiltration and groundwater recharge, shades the water surface helping to maintain cool water temperatures that many native fish and aquatic insect species require, and provides food and structure through debris fall for aquatic organisms. Streams in forested areas tend to be shallow and wide with rocky beds that serve as breeding and nesting sites for aquatic organisms. Forest cover provides the same benefits for ponds and lakes—shading water, adding detritus to water edges, filtering stormwater, and recharging groundwater. A primary threat to water quality and quantity is land conversion and the loss of the benefits natural cover provides.
Key features of healthy streams
Key features of healthy ponds and lakes
Because aquatic ecosystems can be quite complex and multidimensional, gleaning critical hydrologic, habitat, and species diversity information can be difficult. However, describing in as much detail as possible what type of aquatic system it is, its condition, what kinds of plants and animals it supports, and the characteristics of the watershed of which it is a part will help to inform potential management goals and actions. A well-planned and executed inventory can provide the baseline for monitoring studies and adaptive management.
An effective inventory should seek to assess the key features and identify possible issues. While inventories are important, they can be resource intensive. The following categories, Good, Better, and Best, outline three different levels of inventories, which generally follow the availability of resources, expertise, and time. While the Best category can be considered the “gold standard,” any of the three options can provide valuable insights into the condition and health of aquatic ecosystems and resilience in the face of ecological stressors.
Water quality and the condition of aquatic ecosystems can be assessed through evaluation of the system’s chemical, physical, and biological factors. Chemical factors that can be measured include pH, dissolved oxygen, total suspended solids (including algae and sediment), nutrient levels (nitrogen and phosphorus), and chlorophyll a (a measure of algal biomass). These chemistry metrics can influence what species can survive within the water and how safe the water is for drinking and recreation.
Physical characteristics of aquatic ecosystems include light levels, turbidity (the inverse of water clarity), depth, velocity of the flowing water, and temperature.
Species present are powerful biological indicators of the health of an aquatic ecosystem. Knowing the species and population abundances of macroinvertebrates (aquatic animals lacking a backbone including insect nymphs, larvae and adults, crayfish, worms, snails, and clams), fishes, and diatoms (single-celled photosynthetic organisms related to kelp) can provide insight about chemical and physical factors, as different macroinvertebrate species tolerate different levels and combinations of pollution, disturbance, temperature, and other factors. Diatoms and macroinvertebrates also are essential links in the food web supporting fish, amphibians, reptiles, and birds. The presence and abundance of nonnative species are indicators of aquatic ecosystem degradation. Introduced invasive organisms in Pennsylvania waters include: animals such as zebra mussel, grass carp, and northern snakehead; plants such as hydrilla, European water-chestnut, and parrotfeather; and microscopic organisms such as didymo (a colony of organisms also known as “rock snot”). Also, the abundance in surface waters of E. coli (short for Escherichia coli), a bacterium that is abundant in human intestines, is an index of sewage pollution load.
Pennsylvania’s streams have been the focus of water quality assessment by the Pennsylvania Department of Environmental Protection (PA DEP) as well as many conservation organizations, colleges and universities, conservation districts, and watershed associations. These data are often publicly accessible; compiling them should be the first step in determining the quality and condition of a stream or other water body. A few suggested resources are (see Related Library Items for noted resources):
Comprehensive assessments for indicators of stream health are critical in conservation and restoration of aquatic ecosystems; however, methods to determine chemical, physical, and biological parameters of ecosystem health often require expensive equipment and know-how and may be out of reach for many. Visual assessments are a basic qualitative approach to evaluating multiple physical parameters of aquatic ecosystems. A visual assessment protocol converts qualitative observational information to numerical scores, and can be easily implemented by staff and volunteers. Visual assessments conducted consistently allow for comparison between sites, types of aquatic habitat, regions, and the same site before and after management activities.
Several visual assessment protocols are in use for evaluating streams in our region. One is the visual assessment methodology developed by the U.S. Environmental Protection Agency in its Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates, and Fish. In this protocol, cover, pool substrate, pool variability, sediment deposition, channel flow status, channel alteration, channel sinuosity, bank stability, vegetative protection, and riparian zone width are evaluated on a scale of 0-20 and are combined to obtain an overall condition score for the reach.
For the most rigorous level of assessment, the physical, biological, and chemical properties of the aquatic ecosystem are measured in the field using specialized equipment to determine the exact value of each parameter linked to water quality. These data are often the first (baseline) data collected in the long-term monitoring of an aquatic system and can be used to determine the effects of restoration activities, the impact of an ecological stressor, or simply as a way of detecting potential problems early.
Monitored physical and chemical water quality parameters should, at minimum, include temperature, dissolved oxygen, and pH. These can be incorporated into a more comprehensive stream evaluation by combining them with visual assessments. Additional parameters that can be measure include dissolved oxygen, total suspended solids, nutrient levels, chlorophyll a, light levels, turbidity, depth, and flow velocity.
Assessment of biological indicators typically focus primarily on aquatic macroinvertebrates and diatoms, and may also include surveys of fish species. Data collection follows detailed procedures developed by regulatory agencies to increase operational transparency and facilitate the use of the data in regulation and litigation, as well as the transfer of data to other organizations through publicly accessible online databases. This type of in-depth baseline inventorying and potential follow-up monitoring may require the services of a consultant or assistance from qualified volunteers such as university students and professors.
For Pennsylvania, a protocol for assessment of macroinvertebrate species indicators of aquatic ecosystem quality is given in PA DEP’s Assessment Methodology for Streams and Rivers. The results of surveys using this protocol are available to the public through an online map viewer (see Related Library Items).
Streamflow is the volume of water that moves over a designated point within a waterway over a fixed period of time, often measured in cubic feet per second. It is an important component of aquatic ecosystem health because of its effects on water quality and the living organisms and habitats in the stream. The species within a waterway are adapted to the stream’s range of flow rates. From a pollution standpoint, streams with lower flow may have less capacity to dilute pollution and be more susceptible to degradation. From a land stewardship perspective, the purpose of streamflow measurement is to gauge whether and to what degree stream and watershed improvement projects decrease streamflow during storms, and to track changes in flow over time due to climate change.
Flows are measured regularly at nearly 400 U.S. Geological Survey gauging stations in Pennsylvania. The data are readily available and should be the first level of streamflow assessment (see Related Library Items). Additional flow assessments can be completed with field measurements using specialized equipment and capacity. Continuous flow monitoring often involves installation of monitoring equipment such as weirs, gauging stations, water wells, and continuous monitors.
The USGS National Water Dashboard’s interactive map can be used to access real-time water data from over 13,500 stations nationwide (see Related Library Items).
Accurately measuring streamflow at each visit to a site is important to gauging the amount of water flowing through an aquatic system and an initial step in repeated monitoring. The USGS has an online resource titled “How Streamflow is Measured) which can be used as a starting point for monitoring (see Related Library Items). https://www.usgs.gov/special-topics/water-science-school/science/how-streamflow-measured
Scientists and engineers involved in detailed flow assessment and monitoring studies will install a set of weirs (small low-head dams to measure water flow), gauges to measure water level, and permanent streamflow monitors to determine the effect of stream and watershed improvement projects, such as stormwater management activities. These methods are used when precise measurements are needed. They are not expensive but do require installation and maintenance.
Waterways (streams, ponds, and lakes) support wildlife and provide clean drinking water and recreational opportunities. Water quality in healthy aquatic ecosystems must be below regulatory standards for pollutants such as nitrogen, phosphorus, sediment, and E. coli. They must also have appropriate structure for aquatic wildlife, such as branches, rocks, gravel, and sand, and a high diversity of native animal and vascular plant species. Having an adequate riparian buffer is critical in achieving healthy waterways.
Key strategies for achieving this goal include:
Many artificial ponds are in agricultural and residential landscapes, surrounded by mowed lawn grass or pasture. As such, they lack the benefits of riparian buffers and are plagued by polluted runoff, excess nutrients, and sedimentation. Such ponds require ongoing intensive management to maintain good water quality. Another option is to convert the ponds to wetlands. This reduces the potential for many problems including algal blooms and eutrophication. Wetlands also slow and filter stormwater runoff.
Converting ponds to wetlands requires careful planning and permitting to carry out. Steps may include establishing an outlet channel or rerouting, creating berms, and installing native plants, both along the edges of the wetland and upslope from the margins to provide a riparian buffer.
Riparian buffers are vegetated areas dominated by native plants along waterways that protect water quality and quantity. Well-functioning riparian buffers minimize soil erosion, keep water temperature low, promote infiltration and groundwater recharge, mitigate flooding, filter nutrients, and provide food and habitat for aquatic organisms. Due to this wide range of benefits, protecting and improving riparian buffers is critical for water quality.
Riparian buffers will become increasingly important as the effects of climate change escalate. Climate change is predicted to increase temperatures and change current precipitation patterns across the state, resulting in more rainfall overall and more intense events, but with rainfall concentrated in the spring and fall and a potential for drought conditions over the summer. Riparian buffers can help mitigate these impacts to water quality, temperature, and flow volume by shading streams and increasing infiltration into groundwater reserves.
It is important to note that riparian zones dominated by invasive species, especially Japanese knotweed, giant knotweed, Japanese stiltgrass, mile-a-minute, and Japanese hops, are ineffective as buffers. Even though they appear to be well-vegetated in summer and fall, those plants’ root systems do not protect against soil erosion and their stems and leaves are so dense that their shade excludes the establishment of native shrubs and trees, which have extensive, fibrous, soil-binding root systems that can stabilize streambanks. Additionally, invasive plants can overrun and kill shrubs and saplings that are already established. Invasive plants die back to the ground in late fall and leave the soil surface unprotected against erosion by rainfall, runoff, and floodwaters through winter and spring. They also preclude the growth of native plants that are essential components of the wildlife food web.
The Stroud Water Research Center (SWRC) and the Pennsylvania Department of Conservation and Natural Resources (DCNR) have spent considerable time and effort developing recommendations for riparian buffers based on research and experience. For riparian buffers to adequately perform their crucial functions, SWRC recommends a forested buffer of at least 100 feet in width on both sides of a stream and around a pond or lake. SWRC has found that this width is effective in shading waterways, protecting streambed habitat, adding large woody debris, maintaining appropriate stream width and velocity, and removing pollutants including nitrogen and phosphorus. A width of 100 feet is the minimum recommendation. A wider forested buffer can provide even greater benefits.
Although a forested riparian buffer is typically recommended as the best management practice for water protection, this is sometimes not possible due to roots interfering with underground pipes. Woody shrubs also may not be an option for the same reason. In instances where streambanks have been disturbed and woody vegetation cannot be used, herbaceous plants with deep roots, especially native warm-season grasses, can be enough to hold a streambank. Herbaceous plants that thrive in riparian areas should be chosen for streambank stabilization.
DCNR recommends utilizing multi-functional riparian forest buffers to provide greater flexibility for landowners in terms of design, width, and plant species. This approach to riparian buffers includes a “no management” zone closest to the waterbody that is comprised of native plants, particularly trees, and is stewarded to control stressors like invasive plants. Outside of this zone, the land manager may include species that provide an economic benefit such as fruit and nut trees or shrubs with edible fruit like elderberry.
Generally, installing riparian buffers involves planting and maintaining native plants along the bank of the waterway. The species composition should include a diverse mix of native plant species that will thrive in riparian conditions. The plants must be tolerant of periodic inundation, soil compaction, and disturbances associated with floodplain ecosystems. The wider and more species-diverse a riparian buffer is, the more likely it will provide the desired ecological functions. Riparian buffers should have a minimum width of 100 feet.
Where riparian buffers are less than 100 feet in width, or where a land manager has a desire and resources to further increase the width, trees can be planted to establish a buffer. Trees can be spaced 15 feet apart, or approximately 200 trees per acre. Unless the entire area is fenced and the fencing is high enough to prevent deer from entering, all trees should be protected with tree shelters. The shelters need to be maintained to prevent damage by voles and encroachment by other plants. More information on planting and tree selection can be found in Tree Selection and Planting. Climate change should also be considered when planning planting time, tree size, and species (see Forest Management and Climate Change). Climate change may make establishment more difficult due to increased storm frequency and flooding intensity.
Stroud Water Research Center has created a library of resources for riparian buffer establishment and maintenance (see Related Library Items).
Good—Plant and maintain a 100 foot-wide buffer of native trees. The management objective should be to install a dense riparian buffer that is at least 100 feet in width made up of a diverse mix of native trees. Use resources such as the Pennsylvania Natural Heritage Plant Community Predictor Tool for Site Restoration to select species that will thrive at a specific site, based on data collected by Pennsylvania Natural Heritage Program ecologists. Typical trees include American sycamore, silver maple, eastern cottonwood, river birch, black willow, American elm, honeylocust, and eastern box-elder. Cultivars should be avoided to best support native wildlife, particularly pollinators.
Better (in addition to Good) —Plant and maintain a 100-foot buffer of native trees and understory. Typical understory plants include shrubs such as silky dogwood, red-osier dogwood, northern and southern arrow-woods, ninebark, buttonbush, and shrub willows; warm-season grasses such as Indian-grass, big bluestem, switchgrass, and northern wood-oats; cool-season graminoids such as deertongue, Virginia wild-rye, soft rush, woolgrass (a bulrush), and Carex sedges; and perennial forbs such as Joe-Pye-weeds, common wingstem, cutleaf coneflower, swamp milkweed, ironweeds, various wetland goldenrods and asters, and many others.
Best (in addition to Good and Better) —Plant and maintain a wider than 100-foot buffer of native trees, shrubs, and herbaceous perennials with well-developed structural layers.
Under natural conditions, the areas adjoining rivers, streams, lakes, and ponds are protected by forested riparian buffers of plant species tolerant of flooding and inundation. These transitional areas (partially upland, partially wetland), play an important role in maintaining aquatic ecosystems and provide significant ecosystem services for people, such as limiting erosion and downstream impacts of catastrophic flooding. The loss of a riparian buffer has an adverse effect on the quality of water and aquatic habitats, limits the overall benefit to wildlife, and limits the ecosystem services a site may provide. Without the protective canopy and filtering and stabilizing root systems of riparian vegetation, streams can be degraded by thermal pollution and higher levels of total suspended solids, nutrients, and bacteria from stormwater runoff and nearby farms (livestock, fertilizer application) and homes (failing septic systems, lawn fertilizers).
Decades of deforestation, agricultural expansion, and increasing suburban development have drastically reduced the extent of water edge protected by forest in Pennsylvania. However, in some watersheds, the combination of fewer acres in agriculture and better management practices promoted by the U.S. Department of Agriculture’s Natural Resources Conservation Service have resulted in more miles and increased quality of riparian buffers. Nonetheless, there is much more work to do.
Water quality is degraded by erosion, sedimentation, and serious flooding associated with ineffective management of stormwater from impervious surfaces. Uncontrolled roadside runoff (which often contains oils, metals, and road salt) from ditches and culverts is a region-wide problem. Severe erosion impacts are readily evident along stretches of headwater streams, particularly in certain agricultural settings where functioning vegetated buffers have been lacking for many years and livestock are allowed to trample streambanks and stream bottoms. Sediment is generated by stormwater runoff and associated soil erosion from streambanks, farm fields, and construction sites. Excessive sediment in streams, lakes, and ponds inhibits fish reproduction by smothering eggs and harms other aquatic life, particularly bottom-dwelling species that live among pebbles and cobbles, which are important links in the aquatic food web.
Unfortunately, forests are often seen as a good place to direct concentrated runoff from farm fields and roads. While forest cover and forest soils can capture and absorb precipitation better than any other land cover, forest vegetation is not good at protecting soils and surface waters from pollutants and sediment in runoff from major storms, especially in watersheds with large amounts of impervious surfaces or agriculture. Frequently, gullies are gouged within forests by stormwater runoff from adjacent agricultural or residential areas.
Residences in local watersheds may contribute to high fecal bacteria, nitrogen, and phosphorus pollution from failing septic systems and use of phosphate-based detergents. Nitrogen and phosphorus often contaminate runoff from lawns and gardens where chemical fertilizers are used. Phosphorus is the main nutrient responsible for eutrophication (nutrient enrichment, which causes algal blooms) in waterways. As algae die off, dissolved oxygen is consumed by decomposing bacteria, potentially suffocating healthy populations of fish and other aquatic life. Residents can exacerbate streambank erosion and sedimentation by mowing and dumping lawn debris near streams (which prevents the growth of trees and shrubs with root structures that can stabilize the soil) or filling wet areas that slow and absorb stormwater.
The presence of cattle and horses in streams and wetlands can degrade stream quality through trampling and erosion of streambanks and input of waste material. Dogs, even though they are smaller, can have a similar impact on streambanks and water quality, including inputs of nutrients, sediment, and fecal bacteria.
Addressing these issues of nonpoint source pollution depends on addressing the sources of pollution and maintaining a healthy riparian buffer. A healthy riparian buffer will help mitigate these issues. Where next to a pasture, a fence is recommended to keep livestock out of the buffer and away from the waterway. Livestock access to a stream may be limited to a small area, or preferably by providing an alternative water source. Short-duration grazing may be allowed within some riparian buffers, but grazing should not occur when soil is wet, when plants are emerging or setting seed, or when plant cover is limited or stressed by dry conditions. See Forest Management for more information about how to create and manage a riparian buffer.
Green stormwater infrastructure can also be used to manage stormwater. Structures such as planted swales, infiltration trenches, detention basins, and retention ponds can retain, filter, and infiltrate stormwater prior to it reaching a waterway. Additional information can be found in the Stormwater Management section below.
Finally, outreach and education to surrounding landowners and visitors to publicly accessible lands can be used to inform people about the risks associated with stormwater runoff, particularly regarding household pollutants and pets.
Year-round Canada goose populations can cause unnaturally high levels of fecal bacteria and nutrients in waterbodies. Geese favor waterbodies that have open sightlines and clear access to water, such as ponds and lakes surrounded by maintained lawn. As such, resident geese can be a particularly problematic wildlife species, particularly in agricultural and suburban settings where streams and ponds are surrounded by open, maintained lawn. Installing vegetated riparian buffers of tall native grasses, sedges, forbs, and woody species will make the area less desirable for geese.
In general, management can involve multiple tactics—from passive methods, such as modifying habitat to be less desirable for geese, to more active deterrents, such as harassing geese, use of repellants, and lethal removal. More information on management can be found in the Goose Management section.
Dams, historically built to power mills and facilitate transportation, or more recently for sedimentation and flood control, negatively affect water quality and aquatic habitats, particularly for fish. Dam pools trap sediment and allow greater sunlight exposure. The resulting turbidity, silt-covered stream bottom, and high summer water temperature are conditions that native aquatic wildlife cannot easily tolerate. Reservoirs also attract large numbers of year-round resident Canada geese, adding nutrient and fecal pollutants, and reducing dissolved oxygen. Aquatic wildlife migration patterns also suffer disruption by dams. Although fish ladders are being installed on the largest dams, thousands of dams exist on streams of all sizes across the region, preventing migration of many species, from shad to American eels to stoneflies.
While some dams may still be serving a purpose that balances the aquatic ecosystem harms they cause, many are historical remnants of now defunct mills and transportation corridors. Management of dams should consider current function as well as impact to the environment. At base levels, fish ladders can be installed to facilitate fish movement. At the other end of the spectrum of both beneficial effect and cost, dams can be removed and waterways restored. In between, dams can be modified and maintained to reduce sediment buildup, adjust the depth from which outflow is drawn to reduce downstream temperature, and alter the timing and volume of water releases to benefit aquatic wildlife. Any dam modification or removal will need to go through proper planning and permitting channels. More information about dam management is available through the Department of Environmental Protection.
Good—Install a fish ladder to facilitate upstream and downstream fish movement around the dam.
Better—Modify the dam where it is not providing a critical function to create a water flow regime designed to benefit the downstream aquatic ecosystem. Restore the newly exposed upstream stream channel if the reservoir water level is lowered.
Best —Remove non-essential dams. Restore the stream channel and revegetate new streambanks with native plants selected to thrive best in each of the resulting soil moisture zones, from upland to floodplain to aquatic shallows.
Unnaturally warm water temperatures along some reaches of local streams may exacerbate the impact of nonpoint source pollution on the health of aquatic life. Higher water temperatures are mainly attributable to lack of shade along streambanks, discharge of warm surface water from ponds, and runoff from sun-heated pavement, roofs, and lawn areas. Thermal pollution can trigger a vicious cycle as warm water encourages algal blooms, which absorb more sunlight, further warming the water. As algae die they are decomposed by bacteria, which consume oxygen from the water, further depleting dissolved oxygen.
Reducing thermal pollution involves several management activities that focus on reducing the temperature of the water. These include increasing shade, reducing impervious surface in the watershed and thus reducing stormwater runoff, and increasing groundwater storage using green stormwater infrastructure.
Good—Maintain at least 100 foot wide riparian buffers along waterways and plant native vegetation in and around detention basins (see Riparian Buffer section). Riparian and wetland vegetation shades the water, slows surface flow, which increases groundwater infiltration, and takes up water in the roots and transpires it through the leaves, cooling the air slightly above the surface water.
Better (in addition to Good)—Reduce impervious surfaces within the property, including lawn. Permeable surfaces reduce stormwater flow into the water body by promoting infiltration, growth of vegetation, and slowing the velocity of surface flows.
Best (in addition to Good and Better)—Work with upstream landowners to create and maintain riparian buffer along waterways and reduce impervious surfaces across the watershed to limit thermal pollution at the watershed scale.
Climate change is virtually certain to impact water quality and quantity due to expected changes in precipitation, storm frequency, storm intensity, drought frequency and severity, and temperature. According to climate models, Pennsylvania is expected to get warmer and wetter. At the same time, periods of drought are expected to increase. Winter flooding may be more frequent as warmer temperatures will result in precipitation falling as rain and not snow. This will be catastrophic to mountainous watersheds in the western U.S. that depend on snowmelt to feed streams and rivers. While Pennsylvania may not see as severe an effect from low winter snowpacks, rivers are expected to see more severe winter storms resulting in larger volumes and higher velocities of stormwater flow. This will lead to more frequent and severe floods and increased streambank erosion, especially when vegetation is dormant. It may also lead to a greater amount of pollution, trash, and organic debris (logs, tree limbs, leaves) entering waterways.
Climate change may most visibly impact riparian areas (see Forest Management). Changes in precipitation, temperature, and storm severity, including high winds, may affect the survival of existing trees and the success rate of natural regeneration. Over time, or quickly in the case of severe flood disturbance, this can degrade the quality of the floodplain.
Management should focus on managing stormwater prior to it reaching a waterway. Of primary importance is protecting and restoring the riparian buffer. Additionally, management efforts can focus on green stormwater infrastructure and reducing or limiting impervious surfaces in the watershed. All management activities should consider the expected increases in severity and frequency of flooding events.
Flooding is a natural process whereby streams overflow their banks during and after heavy precipitation or snowmelt and spill into floodplains. In natural settings in this part of the continent, streams typically reach bankfull stage (at the verge of spilling over into the floodplain) and above once every 1½ years, on average. Natural floodplains are ecosystems that share traits with both uplands and wetlands and often are networks of connected wetlands that dissipate the velocity and volume of floodwaters. Intact floodplain ecosystems reduce downstream flooding hazards to agricultural and residential areas.
Much of the agricultural area in Pennsylvania has been cleared of natural vegetation for centuries. This has led to streams cutting deeply into their channels, reducing their ability to overflow their banks and disperse energy into their floodplains. As a result, even more downcutting occurs, further increasing the volume of water that the stream channels carry during storms.
By clearing vegetation, grading and compacting soils, and paving more of the land—even with stormwater management systems in place, we have altered the natural flooding process in a way that prolongs periods of high flow in local streams. The major cause of dangerous flooding is altered runoff patterns, as we plow fields and pave over watersheds, allowing most of the stormwater runoff to head directly into streams rather than recharging into the soil as it would do naturally. The suburban land-use pattern favors seemingly benign single-family residential neighborhoods and shopping centers; however, the construction sites, roads and parking lots, lawns, and sewage systems of this deceptively tame suburban landscape are responsible for the greatest threats to water quality and quantity in many Pennsylvania watersheds.
Effective management requires addressing the issues causing flooding, such as development, and ensuring that natural systems are functioning to the highest extent possible, such as by maintaining or creating adequate riparian buffers. Green stormwater infrastructure can also be used to manage stormwater to reduce flooding.
Groundwater depletion is a serious condition that can lead to drying of local wells and loss of baseflow (water that moves underground) to wetlands and streams. Soils lose their natural groundwater recharge ability when natural vegetation is cleared and replaced with lawn, graded and compacted soils, and impervious surfaces such as paved areas and rooftops. Depletion of groundwater is difficult to monitor, since it requires comparison of groundwater well and stream gauge data over time.
Most local wells are private. When wells go dry, it is difficult to pinpoint the cause; it may be a combination of factors including drought, shallow well depth, increased withdrawals from surrounding wells, and increased impervious surface coverage.
As groundwater supplies diminish, less water reaches the streams that depend on groundwater during dry months. In first and second order streams, decreased baseflow magnifies the concentration, and thus the adverse effects, of pollutants. This results in increased stress on pollutant-sensitive aquatic species. Under drought conditions during dry summer months, some Pennsylvania streams can have so little input from groundwater that 90% of the streamflow is treated sewage discharge.
The quality and quantity of surface and groundwater and the ecological integrity of natural areas are closely interrelated. Increased surface runoff generated by poorly planned development results in increased flooding and erosion, diminished groundwater levels, increased pollution of groundwater and surface water, increased concentration of pollutants, and reduced diversity of native plants and wildlife. The next section provides general guidelines and innovative strategies for areas under suburban development that will minimize the impact to on- and off-site land and water resources.
Managing stormwater runoff from impervious surfaces is an essential aspect of land and water stewardship. Natural areas typically retain far greater volumes of stormwater than agricultural or developed areas. This translates to fewer and less severe floods and more consistent stream baseflows during drought periods. When a natural area is altered to allow for recreation, such as through the installation of trails, or destroyed by conversion to residential or other intensive use, innovative stormwater systems may be used to help compensate for the degradation of natural hydrology by infiltrating and retaining stormwater runoff on-site during storm events and discharging it more slowly; this also helps to maintain a more natural hydrologic regime in nearby streams. Without such interventions and management of stormwater, erosion and water quality and quantity issues are likely to occur that can impact surrounding natural areas.
Eliminating unnecessary clearing, grading, and impervious surface and promoting groundwater recharge can minimize the watershed impacts of development, whether it be for building or recreational amenities. The technique of handling runoff in many small systems close to where it is generated on the site is a major improvement over concentrating runoff in a few large basins at the lowest areas of the site (often where the poorest soils for recharging groundwater are located).
The need to manage stormwater runoff on-site provides numerous opportunities for the land steward to address some of the major water quality issues facing local watersheds. Incorporating current stormwater best management practices (BMPs) can reduce nonpoint source pollution and flooding and increase baseflow.
The previous generation of stormwater systems provided virtually no means of filtering out contaminants from stormwater runoff, other than by allowing suspended solids to settle out in detention or retention basins. In contrast, present-day stormwater BMPs, also known as green stormwater infrastructure, filter runoff to improve water quality. Simply recharging runoff into soil rather than discharging it to wetlands and streams allows the soil and vegetation to remove excess nutrients, chemicals, sediments, and salts from paved areas, rooftops, and lawns. If carefully designed, these systems will not contaminate nearby wells with nonpoint source pollutants. With the addition of innovative techniques such as vegetated filter strips, vegetated swales, sediment forebays, and constructed wetlands (see Recommended BMPs, below), the filtration effects on runoff from each site are significantly enhanced.
Stormwater planning and design strategies include evaluating the entire project from a stormwater perspective, taking into consideration such factors as:
More information for each of these items is included below.
When compared to conventional stormwater management systems, projects designed using this approach can reduce runoff volume and peak rate reaching streams, maintain recharge of groundwater, and enhance the quality of runoff water. If designed properly, the result is less downstream flooding and erosion, cleaner water, healthier aquatic life, and more baseflow for streams and wetlands. The techniques proposed here are consistent with the National Pollution Discharge Elimination System (NPDES) Phase II requirements (see Related Library Items).
These BMPs can also be used in areas that are already developed and are having stormwater issues. Additional information about stormwater management and trails can be found in the Recreation chapter.
Every stream and its floodplain evolve over time in the context of their drainage area’s specific slope, geology, vegetation, and climate. However, as land use (and climate) changes, watershed hydrology changes, so the stream system must adapt to manage the new flows. Streams once buffered by forests that absorb and slow surface runoff must accommodate larger quantities of runoff flowing from suburban landscapes and with higher peak rates—“flashier flooding.” These same streams, which once were fed by a steady flow of groundwater seeping from beneath a natural landscape, may cease flowing in drier months due to depleted groundwater baseflows.
Natural stream systems in Pennsylvania develop a dynamic equilibrium with their floodplain and channel that creates natural areas with moderate sedimentation and erosion, both in the channel and out onto the floodplain. A stream in an undisturbed landscape meanders back and forth across its floodplain, splits into multiple channels and rejoins, and changes its course over time. Streams respond to flashier flood patterns created by land clearing and suburban development by quickly expanding their channels wider, deeper, and straighter.
Broader, more entrenched streams are unable to overflow their banks in a flood, restricting all the erosive velocities to the channel. These streams undercut surrounding vegetation, further destabilizing their banks and causing still more erosion.
Stream channels can be restored to a state that reduces bank erosion and reaches a new, more natural equilibrium. Often, the reason why streams experience accelerated bank erosion and in-stream habitat loss is because of poor stormwater management from upstream land use. This constraint should always be considered in order to set realistic expectations of success from a stream restoration project. If there is a high proportion of impervious surface upstream, with few opportunities to better manage runoff using BMPs or through redesign and redevelopment, the potential for stream restoration to a natural state is limited. In such a case, it may make more sense to stabilize a stream in its existing degraded state in the short term and attempt incremental improvements over the long term.
To restore streams that are constricted within their channels from the vicious cycle of undercutting and bank destabilization, the following methods should be considered.
“Hard engineering” is an approach that emphasizes installation of retaining walls and gabions to lock streams into place in areas where space is limited and in-stream erosion is severe. These devices do little to dissipate energy from accelerated runoff, will likely experience undercutting, and often transfer erosion problems downstream to another site. Therefore, preferred techniques aim to restore natural ecosystem functions in and adjacent to streams. This is known as bioengineering.
Management Objectives
The main objective of bioengineering is to use natural materials and plants to restore degraded streams and protect aquatic habitats. Bioengineering includes a variety of methods.
Live stakes are a dependable, cost-effective way to introduce stabilizing vegetation to under-vegetated streambanks. A number of native shrub species are available that will grow from live stakes (without roots), mainly various species of willows, silky dogwood, and red-osier dogwood. These species readily grow fibrous root systems that help hold soils together and are specifically adapted to a streamside environment. Their flexible stems bend without breaking, dissipating energy from floodwaters and protecting banks from damaging ice flows. They can also be integrated into gabion construction.
Stakes can be purchased commercially or selectively harvested from nearby sources. They are often 18 inches long, ½ to 1 inch in diameter, and are sometimes scarred on the lower end to encourage rapid root growth. Planting is done in early spring when plants (and stakes) are still dormant. A pilot hole is made in the bank using a dibble bar and sledge. Using a rubber mallet, the stake is then driven into the bank at least 12 inches. Stakes should be planted at a 45° angle facing downstream so that currents and floating debris do not rip them out. The lower ends of stakes should be within 12 inches of the normal water line in the stream. Stakes are most successful when invasive species and low-hanging tree branches are removed so they receive sufficient sunlight.
Coconut fiber (coir) logs serve as a short-term bank stabilization tool as well as a growing medium for live stakes and other streamside-stabilizing plants such as soft rush. Made from coconut fiber, they are 18 inches in diameter × 10 feet or more in length and are staked in at the toe of the slope at the water line. They fill with sediment, which becomes an excellent medium in which to grow species with strong fibrous root systems.
Fascines are bundles around 1 foot in diameter of live cuttings from shrubs at least 6 feet long. They are staked into a streambank at or below the waterline, similar to coconut fiber logs. Sometimes a trench can be made at the toe of the bank where a fascine can be staked. The live material will then grow roots and stems while the space between the cuttings will allow sediment to collect to help stabilize the bank.
Fascines of dead cuttings can also be used to buffer streambanks and collect sediment temporarily. These are useful below the water line when eroded voids exist under trees along the bank.
Plantings of container-grown shrubs of native willow species, silky and red-osier dogwoods, buttonbush, black elderberry, smooth and speckled alder, swamp rose, and other wetland species can be used higher on the streambank where soil moisture is too intermittent to plant live stakes.
Bioengineering techniques can help stabilize a mildly degraded streambank. However, where a bank is steep (30°-90°), erosion potential is usually greater than the ability of bioengineering techniques to stabilize it. In these cases, the streambank, or the channel itself, may first need to be sculpted. In Pennsylvania, any earthwork in or near a stream requires a General Permit from the Pennsylvania Department of Environmental Protection.
Management Objectives
Management needs depend on the extent of streambank erosion. This will determine if stabilization or channel modification is needed.
Bank regrading, where a streambank’s slope is 30°-90°, can be considered if it is accompanied by effective bioengineering practices. The simplest form of bank regrading entails removing soil above the water line to reduce steepness, ideally to a 3:1 slope (3 feet horizontal for each 1 foot vertical, or 18°). Erosion-control fabric is staked in to protect new seeded areas and plantings until their roots have spread. However, where valued existing trees or their roots are on the slope or the working area is limited for other reasons, the technique must be modified. Every stream is different, and one method does not fit all conditions. All streambank modifications should consider upstream land-use changes, the likelihood of the project’s long-term success, and downstream effects of new flow patterns.
Hydrogeomorphology or fluvial geomorphology is a multidisciplinary field of study that analyzes local topography, soils, and climate to optimize stream geometry. The recommended geometry based on such a study includes specifications on entrenchment and sinuosity of the stream in order to mimic natural stream patterns. In extreme cases, modifying stream geometry may lead to actual earthwork within the stream to help restore equilibrium. This could include a variety of methods such as J-hook vanes and log deflectors. These and other, similar structures are used to slow and redirect water to protect eroding banks.
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Environmental Protection Agency, National Pollution Discharge Elimination System (NPDES) Phase II requirements (https://www.epa.gov/npdes, as of 2024)
Pennsylvania Department of Environmental Protection: Looking Below the Surface—PA DEP's macroinvertebrate dataset for stream assessments (gis.dep.pa.gov/macroinvertebrate/index.html, as of 2024)
Pennsylvania Department of Environmental Protection: Stream Improvements (dep.pa.gov/Business/Water/Waterways/Flood-Protection/Pages/StreamImprovements.aspx, as of 2024)
Pennsylvania Department of Conservation and Natural Resources: Forest Buffers Along Waterways (http://dcnr.pa.gov/Conservation/Water/RiparianBuffers/Pages/default.aspx, as of 2024)
Pennsylvania Fish and Boat Commission: map resources on aquatic resources (https://www.fishandboat.com/About-Us/PFBC-by-Region/Pages/MapResources.aspx, as of 2024)
Pennsylvania Natural Heritage Program: Aquatic Community Classification (https://www.naturalheritage.state.pa.us/aquatic.aspx, as of 2024)
Stroud Water Research Center: Macroinvertebrate Identification Key (stroudcenter.org/macros/key/, as of 2024)
Stroud Water Research Center: Watershed Restoration Resources and Fact Sheets (stroudcenter.org/restoration/resources/, as of 2024)
U.S. Environmental Protection Agency: Constructed Wetlands (epa.gov/wetlands/constructed-wetlands, as of 2024)
U.S. Geological Survey: Current Conditions for Pennsylvania—Streamflow (393 sites) (waterdata.usgs.gov/pa/nwis/current/?type=flow, as of 2024)
U.S. Geological Survey: How Streamflow is Measured (usgs.gov/special-topics/water-science-school/science/how-streamflow-measured, as of 2024)