Drainage network

Step 9.1 Identify the Effluent Discharge Points. Determine the points at which wastewater leaves the site. Wastewater may go to an effluent treatment plant, directly to a public sewer, or directly to a watercourse. One factor that is often overlooked in audits is the use of several discharge points. It is important to identify the location, type, and size of all discharge flows. Identify where flows from different unit operations or process areas contribute to the overall flow. In this way, it is possible to piece together the drainage network for the site. This can lead to startling discoveries of what goes where ... 

The Ebro watershed has a large surface area (85,000 km2) and a complex drainage network (a total of 347 streams). The Ebro is a relatively well known river from the point of view of the biological communities composition. Studies exist on the aquatic fauna and flora [3]. However, the functional activity of the river is largely unknown, mostly because of its complexity and associated technical difficulties. This chapter provides a state-of-the art of the who is who in the biological communities in the river, as well as considerations about the threats imposed by habitat deterioration, eutrophication, pollution and species invasions, and indicates the current gaps that still exist in the knowledge of the river. 

Montesanto B, Tryfon E (1999) Phytoplankton community structure in the drainage network of a Mediterranean river system (Aliakmon, Greece). Int Rev Hydrobiol 84 451 —468... 

Servais, P., Garcia-Armisen, T., George, I., and Billen, G. (2007). Fecal bacteria in the rivers of the Seine drainage network (France) Sources, fate and modeling. Sci. Total Environ. 375, 152-167. 

Virtually all watersheds of any size have been altered by human activity. The removal of vegetation, propagation of impermeable surfaces, and installation of drainage networks alters hydrologic flows and their contact with organic matter reservoirs. Development also has the effect of replacing diffuse sources of DOM with point sources. Wastewater effluents may contain substantial amounts of DOM and are often enriched in DON and DOP relative to natural influents (see Chapter 2). 

Richards, R.P. and D.B. Baker (1993). Pesticide concentration patterns in agricultural drainage networks in the Lake Erie basin. Environ. Toxicol. Chem., 12 13-26. 

BiUen, G., Gamier, A., and Rousseau, V. (2005). Nutrient fluxes and water quahty in the drainage network of the Scheldt hasin over the last 50 years. Hydrobiologia 540, 47—67. 

Gamier,., Bihen, G., Hannon, E., Fonbonne, S., and Videnina, Y., and Soulie. (2002). Modehng transfer and retention of nutrients in the drainage network of the Danube River. Estuar. Coast. Shelf Sci. 54, 285-308. 

Deurer, M., Green, S.R., Clothier, B.E., Bottcher, J., and Duijnisveld W.H.M. Drainage networks in soils. A concept to describe bypass-flow pathways. Journal of Hydrology 272,148-162. 2003. 

Research on the evolution of drainage networks in a simulated loss watershed based on fractal dimension... 

Figure 1. The drainage networks map in six periods in the simulated loess watershed.

As can be seen in the Table 1 and Figure 2, the values of box dimension increase from 1.0935 in 1st period to 1.2013 in 4th period, and then decrease to 1.1836 in 6th period. At the same time, correlation coefficient r in all periods are over 0.99. It shows that the drainage networks became more and more complicated and unbalanced in their early development stage and they tended towards stability with the evolution of the watershed. 

By means of summarizing the number and the length of drainage networks belonging to each order, the Horton dimension values of the drainage networks in each periods can be calculated when Rg and Rg are acquired (Table 2). 

According to Horton s research that the Rg values of natural drainage networks vary from 3 to 5 and their Rl values vary from 1.5 to 3.5, the values of Rg and Rg in the simulated watershed are in accordance with the conclusion. As we know, the value of Horton dimension is determined by the ratio of Rg and Rg, the values of Horton dimension would increase when Rg rises and Rg reduces with the development of the watershed in the early stages. While the watershed came to balanced, the values of Horton dimension would decrease and keep regular as the drainage networks get simple and dynamic. 

Table 1. The box dimension values of drainage networks in the simulated watershed.

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