NOTICE: With the exception of 01467200, calibration of water-quality instrumentation is conducted exclusively by Philadelphia Water Department personnel with USGS oversight. Erroneous or missing data, resulting from instrument malfunction, are not the responsibility of USGS.
Discharge (Q): The amount of water flowing in a stream or river at a particular time. This flow comes from two main sources - baseflow and stormwater. Baseflow is the relatively constant flow of water from natural springs and rain water that has infiltrated into the ground (groundwater). When it rains, stormwater runoff flows into the stream or river, increasing the discharge. All of Philadelphia's streams drain areas with lots of streets, roofs, sidewalks, and other places where the rain cannot soak into the ground, so the stream discharge changes very quickly when it rains.
Units of measure= cubic feet per second
pH: pH measures how acidic or how alkaline a solution is on a scale from 0-14, with 7 being "neutral" (neither acidic or alkaline). Smaller values indicate greater acidity while larger values indicate greater alkalinity. Stream pH may fluctuate over the course of the day because of biological activity. Most plants and animals do best in fairly neutral water with a pH range of 6.5-8.0, and more extreme values (either high or low) are undesirable. While Philadelphia's streams generally have relatively neutral pH conditions, some streams in Pennsylvania are affected by acid mine drainage (AMD), and have very low pH, creating inhospitable conditions for fish and other aquatic life.
Dissolved oxygen (DO): The amount of oxygen gas that is dissolved in water. Just like humans, most living creatures in our watersheds need oxygen to survive. Instead of using lungs to breathe oxygen in the air, many aquatic animals get oxygen from water, using gills to breathe. As the DO level rises, the gills work more efficiently, but as the DO level decreases, it is much harder for the fish and other aquatic life to get the oxygen they need to live. Dissolved oxygen conditions in Philadelphia's streams change over the course of the day, because plants and algae produce oxygen only during the daytime, while fish, algae and other aquatic life constantly remove oxygen from the water. Streams with an unhealthy overabundance of algae and aquatic life may have very severe fluctuations in DO, even to the point of lethally low DO during the early morning hours. Units of measure = mg/L.
Turbidity: Turbidity is a measure of clarity, or the light scattering ability of water. Light is scattered (reflected in random directions) by particles that are suspended or dissolved in water. Turbidity is measured by a light source shining through the water while a very sensitive light sensor measures the amount of light reflected at a 90 degree angle. If there are lots of small particles suspended in the water, such as clay and silt from streambank erosion, much of the light will not shine straight through the water sample, but be scattered off in different directions. It is natural for turbidity to increase somewhat, along with stream discharge, in response to wet weather. Severe increases in turbidity may indicate sediment pollution from stream erosion, and this fine sediment can be harmful to fish and other aquatic life.
Units of measure = Formazin Nephelometric Units (Formazin is a standard compound used to calibrate turbidimeters)
Photosynthetically active radiation (PAR): Photosynthetically Active Radiation (PAR) sensors measure the intensity of light that plants use for photosynthesis. Plants can use light of wavelengths 400-700 nm. Light is measured as a quantity of discrete particles (called photons) per unit area per unit time. Multiple factors can affect the intensity of light. Solar radiation fluctuates over the course of the day, increasing during the morning, peaking around noon, then declining again as the sun sets in the evening. Seasonal variations are present due to the tilt of Earth's axis. Light is especially intense during the summer months, as the sun is most directly overhead. Variations also occur from day to day primarily due to cloud cover, which reflects light that would otherwise reach Earth's surface.
Gage Height (GH): Gage height is a measurement of how deep the water is at the gage at a given time. By measuring the amount of flow during different conditions, scientists can establish a relationship between the depth of water and amount of flow.
Units of measure= meters
Units of measure= cubic feet per second
Specific Conductivity at 25 C (K): The ability of water to carry an electrical current. Pure water is actually a fairly good insulator, but substances dissolved in water, such as salt (sodium chloride, or NaCl), can help allow electrical current to flow. When the salt dissolves, the individual Na and Cl atoms split apart. The Chlorine atom tends to "steal" a negatively charged electron from sodium, giving the chlorine a negative (-) electric charge and sodium a positive (+) electric charge. These charged atoms are called ions. It becomes much easier for electricity to flow when there are lots of positively and negatively charged ions dissolved in the water. Conductivity depends on the total number and type of ions in the water, not just Na and Cl from table salt. Rainwater tends to be more pure than stream baseflow in Philadelphia's streams, so conductivity may decrease during storm events. Conductivity may increase during winter, when ions from snow melt salts can run off into the stream.
Units of Measure= mS/cm.
Precipitation (PPT): Amount of water (e.g. rain, sleet or snow) falling at a given place. For example, a coffee can could be used to estimate precipitation. If one inch of rainfall occurs, there would be approximately 1 inch of water at the bottom of the can. However, this method would not be very useful for measuring very small amounts of rain. The USGS rain gage uses a large, funnel-shaped collector so it can catch rain over a much larger area. This increased sensitivity also allows the rain gage to measure how much rain falls in a relatively short amount of time, as short as 15 minutes. In this way, scientists can examine not only how much rain falls in total, but also how intense the precipitation is at different times during a rainstorm.
Units of measure = inches
L= Photosynthetically active radiation (average flux density on a horizontal surface during measurement interval), micromoles of photons per square meter per second ; WT= Temperature, water, degrees Celsius; K= Specific cond at 25C; pH= pH, water, unfiltered, field, standard units; DO= Dissolved oxygen; Q= Discharge; GH= Gage height; WWF= Warm Water Fishery
01474000 - Wissahickon Creek at Mouth, Philadelphia, PA: TSF
L= Photosynthetically active radiation (average flux density on a horizontal surface during measurement interval), micromoles of photons per square meter per second ; T= Turbidity, water, unfiltered, monochrome near infra-red LED light, 780-900 nm, detection angle 90 +/ -2.5 degrees, formazin nephelometric units (FNU); WT= Temperature, water, degrees Celsius; K= Specific cond at 25C; pH= pH, water, unfiltered, field, standard units; DO= Dissolved oxygen; Q= Discharge; GH= Gage height; PPT= Precipitation; WWF= Warm Water Fishery
01465798 - Poquessing Creek at Grant Ave. at Philadelphia, PA: WWF