A door that provides a pocket of air between the main door and the exterior door to improve insulation. Storm doors also protect the main door from wind, rain and ice.
A construction method that uses waste straw left over from crops, such as wheat, oats, barley, rye, rice and flax, after all the food has been extracted. Straw is gathered, baled, compressed and tied together. Bales are placed over a “stem wall” to protect the straw from the ground soil and the straw bales are stuccoed and plastered over for finishing.
According to the Intergovernmental Panel on Climate Change, SF6 is the most potent greenhouse gas that it has evaluated, with a global warming potential of 22,800 times that of CO2when compared over a 100-year period. Sulfur hexafluoride is also extremely long-lived, is inert in the troposphere and stratosphere and has an estimated atmospheric lifetime of 800–3200 years. Average global SF6 concentrations increased by about seven percent per year during the 1980s and 1990s, mostly as the result of its use in the magnesium production industry, and by electrical utilities and electronics manufacturers. Given the low amounts of SF6 released compared to carbon dioxide, its overall contribution to global warming is estimated to be less than 0.2 percent.
In Europe, SF6 falls under the F-Gas directive which ban or control its usage for several applications. Since 1 January 2006, SF6 is banned as a tracer gas and in all applications except high-voltage switchgear.
Hydrological droughts are typically described by a reduction in lake storage, a decrease of stream flow discharge, and a lowering of groundwater levels over large areas, over one year or several consecutive years.
A drought is a more general phenomenon than low flow and can be characterized by more than low stream flows. Droughts can be classified as meteorological, atmospheric, agricultural, hydrological, and water management. Typically, a drought is defined in terms of water availability for various designated uses.
Low flow is the “flow of water in a stream during prolonged dry weather,” according to the World Meteorological Organization. Many states use design flow statistics such as the 7Q10 (the lowest 7-day average flow that occurs on average once every 10 years) to define low flow for the purpose of setting permit discharge limits.
What factors affect variations in flow?
- Rainfall and snowmelt
- Land use/land cover (e.g., the permeability or imperviousness of surrounding land)
- Water control structures (e.g., reservoirs and dams)
- Water intakes (e.g., for drinking water and industrial cooling)
- Water discharges (e.g., from industries, utilities, and wastewater treatment plants)
- Geological characteristics (e.g., groundwater flow and stream slope)
Do low flows occur at the same time each year?
Most streams will illustrate annual variation that can be explained by seasonal changes in snowmelt, rainfall, and other factors. For many areas in the country, the lowest flows often occur near the end of the summer or beginning of fall. However, each stream is different and any particular year can be an anomaly in terms of if and when low flows occur. The magnitude and duration of low flows can vary significantly from year to year.
Why does a low flow year begin in April while a water year begins in October?
The U.S. Geological Survey defines a “water year” as the 12-month period from October 1 through September 30 of the following year. This definition is appropriate for dealing with water supply and high flow statistics since typically the lowest flows of the year occur in the fall months. However, for low flow calculations, April 1 through March 31 is typically used.