Flow depth of the FWS constructed wetland system, as function of aspect ratio L : W for three population P values: (a) P = 1000 capita; (b) P = 5000 capita; and (c) P = 10000 capita. 

Contexts in source publication

Context 1

... for dense vegetation. Or, in reverse, a certain system’s performance would increase as the vegetation becomes denser. 3. For the commonly used range of L : W and for sparse vegetation the highest flow depths are estimated on the basis of Equation (14) ( a = 5 × 10 7 d − 1 m − 1 ); the lowest flow depths are estimated on the basis of Equation (11) for population more than about 2000 capita ( L : W = 5:1) to 4000 capita ( L : W = 2:1), otherwise by Equation (13) ( β 1 = 1 m 1 / 6 · s). For dense vegetation and L : W = 2:1, the highest depth is predicted on the basis of Equation (12); for L : W = 5:1, the highest depth is predicted on the basis of Equation (12) up to a population of about 4000 capita and Equation (13) ( β 1 = 4 m 1 / 6 · s) for higher populations. The lower flow depth is estimated on the basis of Equation (14) ( a = 10 7 d − 1 m − 1 ) for a population greater than about 3500 capita ( L : W = 2:1) or 1250 capita ( L : W = 5:1), otherwise by Equation (13) ( β 1 = 4 m 1 / 6 · s). From Figure 4 one can conclude the following: 1. For sparse vegetation, the highest flow depth is estimated on the basis of Equation (14) ( a = 5 × 10 7 d − 1 m − 1 ) for the entire population range; for dense vegetation, the highest flow depth is estimated on the basis of Equation (12) for P = 1000 capita, and on the basis of Equation (13) for large populations and aspect ratios. 2. The flow depth increases as the ratio L : W increases. Therefore, increased values of L : W result in increased values of y , which, based on Equation (4), would yield a smaller area requirement (more economic design) for a given hydraulic residence time. Nevertheless, as mentioned, it is not recommended to use L : W > 5:1, and increased depths can be achieved with water surface control at the outlet of the system. 3. A system serving a larger population would be more economic, in terms of unit area (m 2 /capita) requirements, because of the increased depth (see also the following Section 7.2). From this sensitivity analysis of the alternative equations used for the estimation of the flow depth it is evident that differences in flow depth result in differences in the required area, depending on the selected equation. Thus, one can conclude that the research on flow resistance in free water surface constructed wetland systems is not yet complete and probably the more conservative design should be employed. In this study, Equation (14) was selected for use in the following sections, as this equation estimates, for dense vegetation, relatively reduced values of flow depth and consequently relatively increased values of the required area, which leads to a conservative design. Another advantage of this equation is that it can be used for the estimation of the wetland’s flow depth without time-consuming iterations. 7.2. WETLAND UNIT AREA For a FWS constructed wetland system four typical performance criteria can be recognized, which correspond to different disposal ...

Context 2

... FLOW DEPTH The sensitivity of Equations (11)–(14) used for flow depth estimation is analyzed as a function of the population served (Figure 3) and the ratio L : W (Figure 4). Figure 3a presents the flow depth y [m] as a function of the population P [capita], assuming L : W = 2:1, the unit daily BOD production β = 50 g capita– 1 d– 1 , the unit flow rate q = 0 . 15 m 3 capita– 1 d– 1 and t = 5 d. Figure 3b presents the flow depth y [m] as a function of the population P [capita], assuming L : W = 5:1, the unit daily BOD production β = 50 g capita– 1 d– 1 , the unit flow rate q = 0.15 m 3 capita– 1 d– 1 and t = 5 d. The two graphs cover the common range of aspect ratio L : W (between 2:1 and 5:1). Graphs 4a, 4b and 4c in Figure 4 present the flow depth y [m] as a function of the ratio L : W , assuming three populations served, namely P = 1000, 5000 and 10000 capita, respectively. For all three, β = 50 g capita– 1 d– 1 , q = 0.15 m 3 /capita − 1 d − 1 and t = 5 d. As mentioned, in Equation (13), for sparse vegetation β 1 = 1 m 1 / 6 · s and for dense vegetation β 1 = 4 m 1 / 6 · s, and in Equation (14) for sparse vegetation a = 5 × 10 7 d– 1 m– 1 and for dense vegetation a = 10 7 d– 1 m– 1 ...

Context 3

... FLOW DEPTH The sensitivity of Equations (11)–(14) used for flow depth estimation is analyzed as a function of the population served (Figure 3) and the ratio L : W (Figure 4). Figure 3a presents the flow depth y [m] as a function of the population P [capita], assuming L : W = 2:1, the unit daily BOD production β = 50 g capita– 1 d– 1 , the unit flow rate q = 0 . 15 m 3 capita– 1 d– 1 and t = 5 d. Figure 3b presents the flow depth y [m] as a function of the population P [capita], assuming L : W = 5:1, the unit daily BOD production β = 50 g capita– 1 d– 1 , the unit flow rate q = 0.15 m 3 capita– 1 d– 1 and t = 5 d. The two graphs cover the common range of aspect ratio L : W (between 2:1 and 5:1). Graphs 4a, 4b and 4c in Figure 4 present the flow depth y [m] as a function of the ratio L : W , assuming three populations served, namely P = 1000, 5000 and 10000 capita, respectively. For all three, β = 50 g capita– 1 d– 1 , q = 0.15 m 3 /capita − 1 d − 1 and t = 5 d. As mentioned, in Equation (13), for sparse vegetation β 1 = 1 m 1 / 6 · s and for dense vegetation β 1 = 4 m 1 / 6 · s, and in Equation (14) for sparse vegetation a = 5 × 10 7 d– 1 m– 1 and for dense vegetation a = 10 7 d– 1 m– 1 ...