Erosion-controlled systems

FIGURE 6.28 Schematic diagram of a drug diffusion/polymer erosion controlled system containing a dispersed drug. 

FIGURE 6.29 Effects of drug diffusion, pofymer erosion, and drug loading on the drug release kinetics of drug dissolution/polymer erosion controlled systems. 

Drug release phenomena from swelling-and-erosion-controlled systems are much more complicated and have been described mathematically. Diffusion equations of three transporting materials (i.e., solvent, drug, and polymer) are ... 

Zero-order release kinetics expressed by Equation (6.139) agree with Equation (6.126) for heterogeneous erosion-controlled systems. However, when the rate of polymer erosion is very slow, the rate of drug diffusion through the swollen gel layer controls drug release kinetics (i.e., B2 A), and Equation (6.134) becomes ... 

Two of the leading causes of failure in hard armour, such as rock riprap or concrete block systems along shorelines and waterways, are soil migration and hydrostatic pressure buildup. To relieve the hydrostatic pressure and prevent the soil migration beneath the hard armour erosion control systems, nonwoven geotextile can be used as filter (Advanced Drainage Systems Inc., 2015). 

The ultimate goal of erosion control on most constmction sites is to prevent soil and seed loss from areas of soil disturbance until the seed can germinate and establish. Thus, most erosion control systems are temporary in scope and are used to hold the seed and soil in place until the required coverage of vegetation is achieved. However, some erosion control systems are intended to be permanent. These systems remain permanently in place, reinforcing the vegetation long after establishment. 

Hydraulic and water resources engineers are concerned with the flow of water through ditches, conduits, canals, dams, and estuaries. They use their special knowledge of fluid mechanics to design dams, irrigation systems, municipal water works, and drainage and erosion control systems. 

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