Stream Habitat
Stream habitat is one of the important factors that affect aquatic communities. Stream habitat describes the quality of the place or environment where wildlife live.
In Montgomery County, poor habitat is usually the most likely cause of a lack of aquatic species diversity, poor health, and decreased population sizes. Degraded in-stream habitat often results from uncontrolled storm water runoff and uncontrolled runoff from intensively grazed or cultivated agricultural land.
Other reasons for poor stream habitat include altered stream flows, excess sediment, and a loss of surrounding trees and shrubs that help slow the erosion of the stream. Chemicals and pollutants also negatively impact stream habitat.
How does stream habitat affect the aquatic community and the environment?
Stream habitat affects the aquatic community in many ways.
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Too much sediment can smother bottom living organisms and communities by filling in the spaces between the stream bed material that the aquatic community needs for respiration and habitat space.
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Lack of stream cover can impact the fish community by removing places for them to hide and rest.
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Lack of clean stream gravel, clean running water and small pools removes places aquatic organisms need for egg laying and for nurseries for small fish fry.
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Lack of riffles, pools and runs can impact separate life stages of aquatic organisms.
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Murky, cloudy water prevents fish from seeing their food.
- Too much sediment can cover the gills of aquatic insects affecting their ability to respire
In addition to habitat conditions in the stream, the condition of the adjacent stream banks and stream valley also affect the aquatic community. Some of the problems in the stream valley and stream bank include:
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Uncontrolled access by agricultural animals into the stream causing siltation and muddy conditions.
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Lack of trees on the bank to provide shade for cooler water conditions.
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Stream bank erosion caused by mowing up to the edge of the stream.
Stream habitat is monitored by the DEP every time a stream is monitored for either aquatic insects or fish.
Habitat Assessment Activities
Stream habitat is assessed in the field by trained biologists using a set of ten habitat features that rank important physical habitat attributes * .Each habitat feature is scored by two biologists who work together as a team to assess each specific habitat attribute. Habitat features are ranked into a category (i.e.: optimal, sub-optimal, marginal, or poor) using well defined criteria. All rankings are done through observation by the team, no direct measurements are taken.
The County reduces subjectivity and personal biases in using this visual based ranking method by having everyone on the monitoring team attend and successfully complete a calibration session. The habitat assessment is always done by 2 people so the final ranking represents a ‘compromise’ between the 2 staff that actually reduces variability among raters.
Each habitat parameter is given a score from 0 to 20. For cases where each side of the stream is assessed separately (e.g., stream banks), each side is scored from 0 to 10. There are a total of ten habitat parameters, so the highest possible score is 200.
The ten habitat parameters are as follows:
1. In-stream Fish Cover
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Measures: quantity and quality of a variety of stable in-stream structures that provide cover for fish.
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Natural in-stream structures include:
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root wads
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undercut banks
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deep pools
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boulder cover
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Generally, the greater the variety of available cover, the better.
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Artificial structures are also beneficial to fish populations.
2. Epifaunal Substrate
- Measures: quantity and quality of a variety of in-stream structures that provide living spaces for benthic macroinvertebrates .
- Natural structures that increase the amount of dissolved oxygen (e.g.: riffles) are beneficial to the benthic macroinvertebrate community.
- Heterogeneous structures that offer more variety of habitats (e.g.: various sizes of riffle substrate) are better than homogeneous structures that offer less variety.
3. Embeddedness
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Measures: the extent that riffle substrate (e.g.: gravel, cobble, and boulders) are embedded with silt, sand, or sediments.
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The filling in with sediment in between rocks within the riffle reduces:
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the amount of available habitat
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the amount of oxygen that is produced by the action of water flowing through the riffle.
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4. Channel Alteration
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Measures: human-caused changes to the size and shape of the stream channel. (Example: many streams in urban areas were transformed into concrete to transport water or to restore banks.)
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Effects:
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less suitable habitat for benthic macroinvertebrates and fish.
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disrupts the aquatic communities with hydrologic impacts during high flows.
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Artificial support structures for the stream banks (e.g.: rip-rap or concrete sidewalls) indicate the need for unnatural repair processes to streams that have already been damaged from the effects of urbanization.
5. Sediment Deposition
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Measures: the accumulation of sediments within the stream channel
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Sources of accumulation:
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within the stream channel (i.e.: bank erosion)
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from outside of the stream channel (e.g.: uncontrolled runoff from construction sites).
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Effects of high levels of sediment:
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an unstable environment that is continuously changing.
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unsuitable environment for aquatic organisms, especially benthic macroinvertebrates.
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6. Riffle Frequency
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Measures: relative frequency of riffles within a stream compared with the width of the stream channel.
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Importance of riffles:
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are a high quality habitat for benthic macroinvertebrates.
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more riffles means more available benthic macroinvertebrate habitat, which ultimately leads to a greater amount of food for fish.
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7. Channel Flow Status
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Measures: the degree to which the stream channel is filled with water.
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Channel Flow Status is:
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most closely affected by sediment deposition. (The more sediment there is in the stream, the more channel bars are formed, and the less the channel is filled with water.)
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assessed by observing whether the water reaches from bank to bank or whether there are parts of the channel exposed.
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most influenced by natural factors such as drought or flooding.
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When there is less water in the channel, there are also fewer habitats available for aquatic organisms.
8. Bank Vegetative Protection
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Measures: the amount of the stream bank (on the top and along the sides) that is covered by rooted (as opposed to overhanging) vegetation.
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Root systems are important to help to stabilize the banks. (The greater the variety (i.e., trees, shrubs, herbaceous) of bank side vegetation the greater the stability of the bank.)
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Native vegetation is much more desirable.
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Invasive exotic vegetation typically have shallow root systems that are poorly suited to stabilizing the soil and tend to crowd out more desirable native vegetation.
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Some exotic vegetation (e.g., multiflora rose) that grows on top of the banks hangs over the sides of the bank and shades out vegetation that could have kept the banks stable.
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Soil that is colonized by exotic vegetation is more prone to erosion than solids with a mixture of native vegetation.
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Exotic vegetation tends to establish itself as a single dominant species crowding out a more desirable mixture of native vegetation which also is less stable.
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9. Bank Stability
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Measures: quality of bank side vegetation; closely related to bank vegetative protection.
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The better the quality of bank side vegetation, the more stable the banks, and vice versa.
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Unstable banks are also a source of sediment for the streams.
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Signs of an unstable bank include dewatered and exposed tree roots, crumbling, sloughing, and exposed soil.
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10. Riparian Vegetative zone and width
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Measures: the transitional zone between terrestrial and aquatic habitats, usually corresponding with the flood plain area.
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This is the only parameter that does not assess the condition of the stream itself, but rather the land immediately adjacent to the stream.
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Importance of riparian zone:
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serves as a buffer between the stream and the uplands.
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shades the stream from thermal impacts.
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slows down runoff to the stream to control erosion
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traps nutrient runoff that would otherwise end up in the stream.
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The wider the riparian zone and the more diverse the vegetation within the riparian zone, the better the condition of the stream.
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A variety of predominately native vegetation within the riparian zone is of higher quality than a riparian zone dominated by a few species of mostly invasive exotic vegetation.
* Barbour and Stribling: Visual Based Habitat Assessment for Riffle/Run Prevalent Streams
Habitat Assessments Combined with Biological Monitoring
In-stream aquatic biological communities that are found to be impaired often are a result of degraded habitat. The table below describes four possible simplified scenarios relating biological condition to habitat condition. For example, if habitat is degraded, the biological community would be expected to be impaired. However, if the habitat is not degraded, but the biological community is impaired, then chemical contamination is suspected.
| Biological Condition | Habitat Condition | |
|---|---|---|
| GOOD | POOR | |
| GOOD | Not impaired | Not possible |
| POOR | Possible chemical contamination | Habitat probably primary cause |
Improving Habitat Quality with Stream Restoration
DEP restores streams with damaged habitat . For stream restoration to be most effective and remain in place, uncontrolled stormwater flows to the stream must be controlled which often involves retrofitting stormwater management ponds in sequence with the stream.
Water Chemistry
Chemical monitoring provides additional insight into the quality of water every time a site is visited. Occasionally, it is possible to detect a pollution event in a stream by taking note of pH, conductivity, temperature, and/or dissolved oxygen. After noting an abnormal reading, it is sometimes possible to walk upstream to investigate a potential pollution source.
Physical Chemistry Monitoring Activities
The following physical chemistry data is collected at every stream monitoring site:
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pH
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Dissolved oxygen (DO) – the amount of oxygen in the water that is available to biological life, including benthic macroinvertebrates and fish
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Conductivity
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Water Temperature
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Air Temperature
Physical and Chemical Monitoring
Stream Channel Surveying
Taking different measurements of a stream channel over time will show how the stream channel changes (or remains stable). These changes are from natural and human-caused influences. The physical shape and features of a stream are necessary for aquatic organisms to survive. Diverse channel features can support healthy aquatic communities. Four measurements are frequently taken to describe stream shape, slope, and stream bed composition:
1. Longitudinal profile
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Is a ‘slice’ down the stream.
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Measures the slope of the stream, and lengths and number of riffles, runs and pools.
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Measurements over time can show trends in sediment build-up or erosion. Looking at these trends, we can see how disturbances such as floods or increased sediment amounts from land-use modify the channel bed.
2. Cross-section profile
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Is a ‘slice’ across the stream.
- Measures the shape of the steam bed, stream banks and the width of the stream channel.
- Measurements over time can show how the stream channel adjusts (widening, getting deeper or shallower) to accommodate the various flows and amounts of sediment it handles.
3. Channel sinuosity
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Is the wavy shape of a stream.
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Streams form into these wave-like shapes because of the amount of flow and sediment they carry.
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Importance of measuring channel sinuosity:
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It compares the stream’s adjustment to flow and bed load.
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A stream that changes from a wavy shape to a straight stream is reacting to increased flow and bed load.
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4. Pebble counts
- Will measure the changes in the composition of the stream bed material over time.
- For example, a stream may go from having mostly large, cobble size particles, to having mostly sand and gravel size particles as the stream fills in.
Why is Stream Channel Surveying Important?
A carefully designed monitoring program can be an effective tool for tracking changes to the stream channel that result from both natural occurrences and changes in land use; both of which can have profound effects on the shape of the stream.
Longitudinal Profile
A longitudinal profile depicts the down slope gradient of the stream. Measurements of the longitudinal profile taken over time can document trends in aggradation (sediment build-up) or degradation (erosion). Looking at these trends, we can see how disturbances such as floods or increased sediment inputs from land-use modify the channel bed.
The longitudinal profile also shows features such as riffles, runs, and pools. Typically, biological diversity is greatest when a variety of feature types are present (i.e., a combination of riffles, runs, and pools).
Longitudinal profiles, in combination with cross-sectional profiles, are useful in determining the vertical dimension of channel features. Over time, repeated surveys show how the stream channel adjusts (horizontally and vertically) to accommodate the various flows it handles.
Channel sinuosity
Channel sinuosity is important because it reflects the stream's adjustment of its slope to the valley slope. The more sinuous (curvey) a stream is, the more gentle the valley slope.
Pebble Counts
Pebble counts can show shifts in stream bed material composition over time. For example, a stream may go from having mostly large, cobble size particles, to having mostly sand and gravel size particles as the stream aggrades (fills in).
Stream Channel Surveying Activities
The Montgomery County Department of Environmental Protection (DEP) conducts annual geomorphic surveys at 17 separate areas to assess stream channel characteristics. The surveys are performed as part of the requirements for the state NPDES permit. They provide an effective tool for tracking changes to the stream channel that result from natural occurrences and changes in land use; both of which can have profound effects on the stream.
Most of the study efforts to date have focused on the Clarksburg Special Protection Area since it offers the County a unique opportunity to observe changes in the morphology of the stream channel in response to surrounding land use changes. What we learn from indepth study in the Clarksburg SPA will be applied elsewhere in the County as we set the standard for future development requirements to mitigate environmental impacts.
Stream Flow Monitoring
Monitoring of stream flow is a critical component in the assessment of stream structure and stream quality. Stream flow data can be used to:
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Enhance public safety through forecasting and managing floods
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Delineate floodplains
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Determine water quality conditions
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Compute loads of sediment or nutrients being carried downstream
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Design reservoirs, bridges, and culverts
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Compare to rainfall data to depict stream response to local storm events
Stream Flow Monitoring Activities
The Montgomery County Department of Environmental Protection (DEP) and the U.S. Geological Survey (USGS) are working cooperatively to monitor stream flow continuously at numerous stations in Montgomery County, Maryland. These stations include:
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Five stations in the Clarksburg Special Protection Area (2004 to present) to monitor hydrologic changes that occur from changes in land use
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One station in the Northwest Branch of the Anacostia River near Colesville, Maryland (1997 to present) to monitor urban flooding issues and hydrology associated with watershed restoration efforts
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Two stations on Turkey Branch and Good Hope Tributary (2007 to present) to monitor stream restoration efforts in the headwaters of the Rock Creek and Anacostia watersheds
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One station on Sligo Creek near Takoma Park (October 2008 to present) to monitor stream flow. (The County has a long-term goal of establishing a water-quality monitoring program at the Sligo Creek station (if funded) as part of its efforts to reduce pollutant loads in the Anacostia River watershed—including loads from nutrients, sediment, fecal colliform, and trash.)
The following tasks are typically handled during service visits to stream flow-gage stations by USGS hydrologic technicians and/or Montgomery County water quality specialists:
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Checking data recorder operation and gage height relative to the outside reference gage
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Replacement of batteries
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Clearing of sediment or debris from the orifice and purge orifice lines
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Checking and servicing crest-stage gage(s)
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Inspecting the control conditions and removing any leaves, debris, or trash that may be causing backwater at the station
Stream flow data is collected through the stream gages as well as through use of a hand-held velocimeter. The stream gage records the stage, or the height of the water surface above a known elevation, such as sea-level or the gage station. Measurements of the area and velocity of the stream are used to calculate volume passing a particular point in a certain amount of time, or discharge (usually measured in cfs, or cubic feet per second).
After enough measurements of the stage and the discharge are collected, a correlation between the two begins to emerge. This is known as the stage-discharge relationship, and when plotted on a graph it is called a rating curve. It provides a useful tool for land-use planners, engineers, and other interested parties to evaluate stream flow conditions. Since the stage-discharge relationship can change over time, an ongoing record of gage height and discharge data (with mean daily flows and yearly flow statistics) is kept by USGS, along with a record of datum corrections and rating shifts that are required to maintain an accurate stage-discharge relationship. The daily values are published in the USGS Annual Water-Data Report .
The stream flow gages collect a continuous record of gage heights (in 5 minute to 15 minute intervals) by use of a non-submersible pressure transducer system that is interfaced with a Data Collection Platform (DCP). The data is transmitted using a satellite or phone modem in near real-time to the USGS Maryland-Delaware-DC Water Science Center .
Looking for more DEP data? Visit our data page to view all the physical and biological monitoring data sets available to the public.
Map of Stream Gage Locations
Locations of USGS Stream Gages. These gages have USGS site identification numbers. You can access real time flow data from these gages using the USGS National Water Information System Web interface
Additional Resources
Temperature Monitoring
All aquatic organisms have an optimal range of temperature under which they can successfully maintain populations. Some species may be able to tolerate higher than optimal temperatures and survive, but they will not thrive. For example, brown trout can tolerate temperatures above 68 °F (20 °C) indefinitely, but they would not be successful reproducing.
Maryland classifies its waterbodies into Use Classes. Each Use Class has an associated range of species and species function (e.g., adult brown trout survival, or brown trout reproduction). Acceptable temperature ranges are defined so that these species can survive in their particular Use Class.
Class IV Waters
- Use Class IV waters are waters that brown trout can survive in but not reproduce in, hence Use Class IV waters are meant to designate waters that can support a fishery where the brown trout populations are maintained by periodic stocking. An example of Use Class IV waters are portions of Northwest Branch and Upper Rock Creek. Maryland sets a maximum threshold water temperature of 75 °F (24 °C) for Use Class IV waters.
Class III Waters
- Class III waters includes waterbodies where brown trout can reproduce. An example of a Class III water in Montgomery County is Paint Branch. The maximum water temperatures does not usually exceed 68 °F (20 °C). Brown trout are able to reproduce here and stocking is usually not necessary to maintain populations with proper regulations in place (e.g., catch and release fishery).
Class I Waters
- Use Class I waters include all other freshwaters of the state where a maximum temperature of 90 °F (32 °C) should not be exceeded.
What about Class II? Class II is reserved for brackish water and does not apply to Montgomery County streams.
Learn more about Use Classes in Montgomery County
Temperature Monitoring Activities
Given that the concern with temperature monitoring are high temperatures rather than low ones, stream temperatures are monitored from May 31 to September 30, when temperatures are highest. Temperature loggers are placed in specific stream sites during May, and are recovered in October. Loggers are set to record the maximum temperature within a 24 minute period continuously during the time period specified.
DEP monitors temperatures at targeted stream sites where land uses are expected to raise water temperatures (such as in areas that are under construction). Special Protection Areas (SPA) are also subjected to concentrated temperature monitoring. Temperature meters are deployed at specific sites to assess the ability of stormwater or sediment and erosion control devices and systems (otherwise known as Best Management Practices or BMPs) to minimize thermal impacts.
Typically, a temperature logger is placed in the stream, both upstream and downstream of the discharge channel from the BMP. Generally, the temperature of the stream and the water discharging from the BMP is monitored by a consultant hired by the developer.
Precipitation Monitoring
Many stream flow and hydrologic relationships are based on precipitation levels. DEP measures precipitation to properly characterize rain events and relate them to the stream flow response.
DEP maintains two rain gages— both of which are located within the Clarksburg SPA (one in Black Hills Regional Park and one in Little Bennett Regional Park). DEP is investigating re-installing gages in the Paint Branch and Piney Branch SPAs.
Requests for Data
Interested in accessing Montgomery County's biological or stream habitat data? Individuals and groups can file a request for data by contacting the Department of Environmental Protection.