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CONTENTS (Continued)

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48. Earth fill placement 65 (a) Control 65

49. Crushed rock and riprap placement 66

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58. High-pressure gates 75

59. Radial gates 75 (a) Painting 75

CHAPTER VI---TEST INSTALLATIONS

60. Purpose 77

61. Piezometer installation 77

62. Settlement installations 82

APPENDIXES

A. Cost summary 83

B. Pay item breakdown for contract I2r-18601, specifications

No. 2689 90

C. Pay item breakdown for contract I2r-19084, specifications

No. 3047 91

D. Cost of test installations 101

E. Allowable stresses used in gate design 102

F. Design criteria 103

G. List of applicable drawings 105 H. References 106 LIST OF FIGURES

Figure Title Page

Frontispiece Aerial view of Trenton Dam spillway during

dedication ceremonies Frontispiece

1 Aerial view of Trenton Dam 2

2 Trenton Dam location map 3

3 Geological section at centerline of Trenton Dam 4

4 Plan of exploratory holes in Trenton Dam foundation

area 8

5 Plan of borrow areas and logs of several test holes 10

6 Railroad and highway relocation around Swanson Lake

(the reservoir formed by Trenton Dam) 12

7 Flood routing curves 16

8 Trenton Dam--General plan and sections 18

9 Spillway plan and sections 24

10 Downstream face of overflow section of spillway

structure and spillway gates 26

11 Completed spillway structure viewed from right

side of stilling basin 26

12 Spillway gate structure and nonoverflow abutment

sections 28

13 Spillway gate structure--Crest, pier and bridge

details 30

14 General installation of 42- by 30-foot radial gate for

spillway 35

15 Spillway radial gate hoist assembly 36

16 Spillway gate structure--River outlet and gate

control arrangement 38

17 Assembly and list of parts for 6- by 7-1/2-foot high

pressure gate 40

18 Canal outlet works — Plan and sections 42

19 Canal outlet works discharge curves 44

20 Pressure conduit of canal outlet works—Compacting

backfill around conduit 45

21 Canal outlet works—Gate chambers and stilling well

details 46

22 Control house and stilling well for canal outlet works 48

23 Canal outlet works--Gate installations 50

24 Government organization chart—Trenton Dam 53

LIST OF FIGURES (Continued)

Figure Title Page

25 Stripping dam foundation area 60

26 Main cutoff trench excavation operations 60

27 Auxiliary cutoff trench excavation completed to

bedrock 62

28 A side-elevating loader in operation in South borrow

area 62

29 Embankment placing operations 64

30 Dumping riprap rock on an 18-inch layer of crushed

rock blanket 64

31 Panels for forming spillway wall sections 68

32 Form for the 5.5-foot circular conduit being assembled 68

33 View from top of mixing plant showing aggregate un

loading hopper, aggregate stockpiles, and conveyor

system 70

34 Typical concrete mix data 72

35 Workmen using a vibrating screed in finishing a spill

way floor slab 73

36 Placing concrete in a spillway pier with a crane and

bucket 73

37 Laboratory technician preparing plastic tubing for

installation of piezometer tip in the embankment 77

38 Typical terminal well for 40 piezometer tips 78

39 Typical foundation settlement installation 79

40 Settlement point installation details 80

CHAPTER I--INTRODUCTION

1. General Description. - Trenton Dam is located on the Republican River about 2-1/2 miles west of Trenton, Hitchcock County, Nebr. The dam is a rolledearth structure approximately 8, 600 feet long and rises 144 feet above the lowest point of the excavation. A spillway with a maximum discharge capacity of 126, 500 secondfeet, constructed through the left abutment, protects^ the structure from possible flood damage. A river outteTTs provided through the spillway structure for river regulation.,/ At the opposite end of the dam another outlet works is provided to meet irrigation re- ^ quirements. This outlet works forms the headworks for the Meeker Irrigation Canal. An aerial view of Trenton Dam is shown in figure 1.

Tiie_dam is one of the key storage and flood control features of the Missouri River Basin project. Among the benefits derived from the construction of Trenton Dam are flood controls diversion for irrigation, storage, sedimentation control, fish and wildlife preservation, and recreation.

2. History and Authorization. - The extreme drought of the 1930-1940 decade focused nationwide attention on this and surrounding areas in Nebraska and the midwest. Periodic floods with accompanying loss of lives and property damage in the Republican River Valley stimulated further interest of State and local groups in providing protective measures against nature's elements. In the flood of 1935, over 100 lives were lost and much property destroyed. Heavy property damage was also caused by a series of floods in 1947.

The Frenchman-Cambridge division, of which Trenton Dam is part, was authorized as an approved division of the Missouri River Basin development plan by the Flood Control Act (Public Law 534) of December 22, 1944, 78th Congress, 2nd Session. Enders Dam and Medicine Creek Dam, both Bureau dams, are also parts of the Frenchman-Cambridge division. Enders Dam is located near Enders, Nebr., and Medicine Creek Dam 8 miles northwest of Cambridge, Nebr. This development plan was outlined in Senate Document No. 247 as a coordinated plan of the Bureau of Reclamation and the Corps of Engineers, U. S. Army. In July of 1947, funds were appropriated by Congress for an accelerated flood control program, including a specific appropriation of $300, 000 for early construction of Culbertson Dam and Reservoir. The names of these features were changed to Trenton Dam and Swanson Lake, respectively, by Congress upon enactment of Public Law 61 on May 12, 1949.

3. Alternative Sites. - A tentative dam site was selected on the Republican River about 8 miles east of Trenton, Nebr., and 2 miles west of the confluence of Frenchman Creek and Republican River near Culbertson, Nebr. Extensive studies and exploration of the dam site were accelerated by the Congressional action in 1947. Results of studies disclosed unfavorable foundation conditions, a higher than anticipated railroad relocation cost, and necessity for a protective dike at the head of the lake for the town of Trenton. Alternative sites west of Trenton were studied and a site 2 miles west of Trenton was finally selected as the best suited topographically and geologically, which also afforded the most economical railroad relocation. (See fig. 2.)

4. Geology. - In the vicinity of Trenton Dam sedimentry deposits extend to a depth of about 7, 000 feet and rest on pre-Cambrian granites. The lowest and oldest formation exposed during dam construction was Pierre shale, which at the damsite has a thickness of about 1, 000 feet. This shale, deposited during the Cretaceous period, is overlain in the river valley by alluvial sands and on the valley abutments by Ogallala sand and gravel deposits. These deposits at both abutments are capped by a Loveland loess strata about 15 feet thick which is overlain by Peoria loess that forms the upper and surface layer of the region.

The loess encountered at both abutments is composed primarily of fine, loosely cemented, angular grains of fine sand admixed with calcareous particles and small amounts of clay and organic materials. It has low unit weight and varies considerably in density because of the haphazard arrangement of particles and inconsistent amounts of cementing clays and calcareous materials. The average mineralogical composition of samples taken from the abutment is as follows:

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