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THC, the main psychoactive component of cannabis, may only be detectable in saliva and oral fluid for 2–24 hours in most cases. [8] [9] The main metabolite excreted in the urine is 11-Nor-9-carboxy-THC, also known as THC-COOH. Most cannabis drug tests yield a positive result when the concentration of THC-COOH in urine exceeds 50 ng/mL. [10]
The first routine measurements of river flow in England began on the Thames and Lea in the 1880s, [2] and in Scotland on the River Garry in 1913. [3] The national gauging station network was established in its current form by the early 1970s and consists of approximately 1500 flow measurement stations supplemented by a variable number of temporary monitoring sites. [2]
In hydrology, a rating curve is a graph of discharge versus stage for a given point on a stream, usually at gauging stations, where the stream discharge is measured across the stream channel with a flow meter. [1] Numerous measurements of stream discharge are made over a range of stream stages.
A stream hydrograph is commonly determining the influence of different hydrologic processes on discharge from the subject catchment. Because the timing, magnitude, and duration of groundwater return flow differs so greatly from that of direct runoff, separating and understanding the influence of these distinct processes is key to analyzing and simulating the likely hydrologic effects of ...
Digital image correlation and tracking is an optical method that employs tracking and image registration techniques for accurate 2D and 3D measurements of changes in images. This method is often used to measure full-field displacement and strains , and it is widely applied in many areas of science and engineering.
USGS researchers publish the results of their science in a variety of ways, including peer-reviewed scientific journals as well as in one of a variety of USGS Report Series [36] that include preliminary results, maps, data, and final results. A complete catalog of all USGS publications is available from the USGS Publications Warehouse. [37]
Q is the runoff or discharge R is the effective rainfall or rainfall excess or recharge A is the constant reaction factor or response factor with unit [1/T] S is the water storage with unit [L] dS is a differential or small increment of S dT is a differential or small increment of T Runoff equation
Mounted sideways on a wall or bridge piling in rivers or canals, it can measure the current profile from bank to bank. In very deep water they can be lowered on cables from the surface. The primary usage is for oceanography. [4] The instruments can also be used in rivers and canals to continuously measure the discharge.