... dissertation requirement for the Degree of ____ ~D~o~c~t~o~r~o~f~P~h~l~·l~o~s~o~p~h~y ...... He used equations developed by Larson and Allred (1956) ...... The model as discussed earl ier has the advantage of being inex- pensive and ...
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Uni~
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Yitayew, MuIuneh
REUSE SYSTEM DESIGN FOR BORDER IRRIGATION
The University ofArizona
University Microfilms International
PH.D. 1982
300 N. Zeeb Road, Ann Arbor, MI 48106
REUSE SYSTEM DESIGN FOR BORDER IRRIGATION by Muluneh Yitayew
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF CIVIL ENGINEERING AND ENGINEERING MECHANICS In Partial Fulfillment of the Requirements For the Degree of
DOCTOR OF PHILOSOPHY WITH A MAJOR IN CIVIL ENGINEERING In the Graduate College
THE UNIVERSITY OF ARIZONA
198 2
THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE
As members of the Final Examination Committee, we certify that we have read the dissertation prepared by ________~M~u~l~u~n~e~h~Y~i~ta~y~e~W~_____________________ entitled ________~R~e~u~s~e~S~y~s~t~e~m~De:s~l~·g~n~f~o~r~B~o~r~d~e~r~I~r~r~i~g=a~t~i~o~n_______________
and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of ____~D~o~c~t~o~r~o~f~P~h~l~·l~o~s~o~p~h~y______________________________
Date
Date
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Figure 16.
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69
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71
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Figure 20.
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73
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Figure 21.
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74
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Figure 22.
Runoff percentage (a
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75
RUNOFF,
% 10 5
.
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Figure 23.
Runoff percentage (a
DISTANCE (X*)
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76
RUNOFF. %
-
•
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Figure 24.
Runoff percentage (a
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77
Table 8. Given:
Example of the use of dimensionless runoff curves in sloping borders. qin = 2.995 l/s-m;
L = 91.4 m; n = 0.25; k = 5.12 cm/hr a; tco = 47 min.;
a = 0.7;
So = 0.001;
Required: Runoff percentage Maximum advance distance Solution: Reference and dimensionless variables are: 3/5
qi nnleu 315
y
=
(So
_ (0.002995 X 0.25) 0.001
)
= 0.1058m
0.1058
X = Y/So = 0.001 = 105.8 m . T = ~ = 105.8 X 0.1058 = 3739 5 sec = 62.32 min = 1.04 hrs. qin 0.002995 . Z
= kT a
t~o
=
+
kT a = (0.0512)(1.04)0.7 = 0.497 = 0.5 K* = -Y0.1058
tco
47
-r- = 62.32
= 0.754
L* = ~ = 91.4 = 0 864 X 105.8 . Using K*=0.5, L*=0.864 and t co*=0.754 from Figure 20, R equals 22%. This matches the computer results for the same tco*' L*, K* and a values.
The maximum advance distance is obtained for the same tco
value using the zero runoff line and indicates L* = 1.24 from which L is computed to be 131 meters (i.e. 1.24 x 105.8).
78
time and bed slope, and decreases with increase in infi ltrat ion rate, and bed and vegetative drag.
In dimensionless terms it can be viewed as
a function of a, K* and tco*. The importance of this distance is that for design purposes the length. L* should be less than the maximum advance distance X*max· Otherwise the stream will halt before reaching the downstream end of the field.
For X*max greater than L* there wi 11 be runoff in free out-
flow borders.
The advantage of having runoff in free outflow border was
observed from previous discussions. Both Shatanawi (1980) and C1emmens and Stre1koff (1980) presented maximum advance distance as a separate dependent variable by itself using several pages of graphs.
The author's attempt to develop one
curve which would be used to get runoff and maximum advance distance in this study was successful. If one accepts that at maximum advance distance equal to the length of the border no runoff will exist, then it is _obvious to see that the zero runoff curve represents the maximum advance distance for a given dimensionless time of cutoff.
Thus using the data for the given
a, K*, tco* and L* the graphs from Fi gures 9 to 24 are used to get both the runoff percentage R and the maximum advance length.
To ob-
tain the maximum advance distance, the user needs to extend the line for a given tco* up to the zero runoff curve.
The dimensionless distance
that corresponds to the poi nt on the zero runoff curve describes the maximum distance. The method was checked with the other two works and gives exactly the same results.
79
The method has obviously an advantage in that it presents both the runoff and the maximum distance in one page of curves rather than having two separate pages. Optimum Length Another result from this study, which is also helpful in design, is finding the optimum length of the border.
The optimum length is used
here as the length associated with the maximum application efficiency. For given a, K* and tco* the length was varied to the maximum advance distance and the efficiencies checked until reached.
the maximum point is
The distances corresponding to these maximum efficiency points
are then plotted against dimensionless time of cutoff tco* for different K* and an a value of 0.7 and are presented in Figure 25. The curves represent the length that would give the maximum application efficiencies without regard to the other dependent variables. The curves help designers check how close the length used for the particular system is to the length that would give maximum application efficiencies.
80
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