INS 441E WATER RESOURCES COURSE PROJECT

Transcription

1 INS 441E WATER RESOURCES COURSE PROJECT DESCRIPTIVE LEAFLET 1. Introduction it is desired to construct a SEDIMENT DETENTION DAM in order to keep the sediment carried from the basin before it reaches the dam. The design consists of the steps of calculating the possible flood discharge, the dimensioning of the building elements and the safety controls of the structural elements. Construction will be made according to the 500 years flood discharge. 500-year discharge will be calculated by taking into account the daily maximum rainfall data obtained from the rainfall station in the region, and the rainfall values of all groups will be announced. The project file containing the calculation steps and drawings is required to be submitted in a appropriate report format. PROJECT INFORMATION Thalweg elevation : 64 m Maximum water level : 74 m Minimum crest thickness : 2 m Foundation depth for stilling basin : 1-2 m The softwares that is expected to be used to obtain calculate discharge during the project. Google Earth ( Mathwave EasyFit ( Global Mapper ( Aquaveo WMS ( AutoCAD ( MS Office

2 2. Design steps 2.1 Design discharge By using the softwares mentioned above, 500-year flood discharge will be determined by following the steps in APPENDIX-1. In the project report, basin properties (shape of watershed, hydrograph, etc.) should be given visually. The screenshot will be accepted. 2.2 Designing of Sediment Detention Dam Detention Dams generally consist of a vertical barrier (body) constructed on small streams, channels that have used many purposes such as reducing runoff velocity, reducing erosive activities and sediment retention. Design criteria of the overflow spillway are used in order to plan sediment detention dam Spillway crest and wall In order to calculate design discharge of an overflow spillway, Eq. 1 can be used as: Q = CBH (1) Q: Design discharge (m 3 /s) B: crest length (m) C: spillway discharge coefficient H 0 : crest head (m) Relation with design discharge coefficient C and spillway height crest head ratio P/H o given at Figure1. Figure 1. Design discharge coefficient

3 2.2.2 Energy dissipater type Excessive turbulent energy at the toe (cross section (1)) can be dissipated by hydraulic jump at stilling basin (cross section (2)). Energy grade line and surface water profile of a spillway given at Figure 2 schematically. H 0 y 0 P0 y 3 EGL Cross section y 2 y 1 (0) (1) (2) (3) Figure 2. Surface water profile Eq. 2 is obtained according the energy conservation law at cross-section (0) and (1) P + H o = y u 1 2 q2 2g = y gy 2 (2) 1 The positive smaller root (supercritical case) for the unknown water depth y 1 can be solved by Eq. 2. Relation of sequent depth of hydraulic jump y 2 relevant with y 1 as seen Eq. 3. y 2 y 1 = 1 2 ( 1 + 8Fr 1 2 1) (3) The energy lost through the hydraulic jump in a rectangular basin is given by Eq. 4. E = (y 2 y 1 ) 3 4y 1 y 2 (4) Froude number Fr 1 in connection with initial depth of the hydraulic jump y 1 is an important parameter to decide stilling basin type.

4 Case 1: USBR type 1 is proposed for stilling basin design at the case Fr 1 < 2.5. Any energy dissipater structure is not used and the length of apron L 1 is planned according to Figure L 1 /y Fr 1 Figure 3. USBR type 1 length of apron Case 2: Fr 1 > 2.5 The foundation at toe may be excavated by a depth d. Tail water depth y 3 y 3 y 1 = Fr 1 2/3 (5) - If 4.5 < Fr 1 < 2.5 USBR type 4 - If Fr 1 > 4.5 u 1 > 15 m/s USBR type 2 - If Fr 1 > 4.5 u 1 < 15 m/s USBR type 3 Stilling basin is designed according the criteria shown in the Figure 4. Case 3: If the Froude number, Fr 1 > 7 change the spillway dimensions to obtain more stable flow conditions.

5 TYPE 2 TYPE 3 TYPE 4

6 Figure 4. USBR Type 2,3,4, Stilling basin design criteria 2.3 Stability Control Stability controls will be carried out for body and stilling basin under normal conditions without considering extreme conditions (snowmelt, earthquake, etc.). Safety against overturning and sliding tests are sufficient for body. For the stilling basin, it is expected to perform that uplift stability requirements by accomplishing the calculation of pore water pressure Safety against overturning The dam must be safe against overturning for all loading conditions. The factor of safety against overturning is defined as: M r M o 1,5 (6) in which; M r : Total resisting moments about toe, M o : Overturning moments about toe Safety against sliding The dam must be safe against sliding over any horizantal or cracked plane. The safety factor against sliding is given by: f V H > 1 (7) where, f : coefficient of friction between any two planes, V : Vectorial summation of vertical forces acting on the dam, H : Vectorial summation of horizontal forces acting on the dam, Required minimum creep length The following formula will be used to check the creep length. It is expected that necessary precautions will be taken in cases where creep length is not sufficient. L Min= C H (8)

7 2.3.4 Safety against uplift The uplift force and seepage beneath the SEDIMENT DETENTION DAM are examined in order to check whether or not the loads in the downward direction are big enough to resist the uplift force in the upward direction. Gravity Force Uplift Force 1,2 (9) 2.4 Sediment Emptying Time Calculation of the annual average sediment accumulation will be made by using the following formula depending on the basin area. Y = 1906,26 A d 0,953 (10) V = 4980 P 2.83 (11) T = 0.23(Yγ solid ) 0.95 A d V (12) Y: sediment yield (m 3 /km 2 /year) γ solid :26.5 kn/m 3 A: Drainage basin area (km 2 ) V: Reservoir volume (m 3 ) 2.5 Drawing Plan, Cross-section (1), Profile (1) will be submitted. It will be enough to bring the drawings to fit the A3 paper. The dimensions in the drawings should be given in detail. (In order to prepare plan and section files, APPENDIX-2 will be utilized.)

8 2.6 Final Project File 3. Assessments Work package Content Daedline Contribution 1 Design discharge determination (week 5) 20% 2 Structure design and stability control (week 11) 20% 3 Drawings (week 13) 20% 4 Final Report (week 14) 40% Kaynaklar DSİ, Dolgu Barajlar Tasarım Rehberi COFCOF, Ş., Kanal Santrallarında Su İletim Hattı ve Yükleme Havuzları, DSİ kütüphanesi Yanmaz A. M., Applied Water Resources Engineering. 4 th edition. Ankara Erkek, C., & Ağıralioğlu, N Su kaynakları mühendisliği uygulamaları. Beta.