One further estimate, or rather half estimate, which may be called No. 6 is the final and accurate statement of quantities built. This statement taken in connection with the final and accurate, or rather the pertinent and binding, estimate of cost (i.e., unit prices of Estimate No. 5) forms the final estimate or basis of payment for the work.
In thus outlining the nature and functions of the various Estimates Nos. 1 to 6 it is not intended to convey that the sequence of events is more than approximately stated. In any actual case a greater or less number of estimates may be made, they may merge into one another or serve the purposes of each other more or less. It is intended to convey that during the history of the project various estimates are required for various purposes, that normally each successive estimate is a step toward accuracy and that its expense is justified by the result of a previous estimate.
Obviously it is desirable that each estimate should approximate (as nearly as the available time and money will permit) to the accuracy of Estimates Nos. 5 and 6, in order that no injustice may be done to any of the interests concerned. Special attention is also invited to the importance of the estimates here designated as Nos. 2 and 3. Estimate No. 2 is a presentation of the case and No. 3 is practically an answer as to whether or not the project shall be undertaken. Each of them may be divided into (a) an estimate of cost and (b) a presentation or discussion of all collateral pertinent features upon which a judgment or estimate of the possible returns may be made. A treatment of the collateral features is outside the scope of the present work; they will not be here discussed except to say that as presented with Estimate No. 2, while they are often unduly optimistic, yet in a surprising number of instances some favorable feature is entirely overlooked or presented in an entirely inadequate manner. The optimism will be properly discounted by Estimate No. 3 and accompanying report, but the overlooked favorable feature may not be discovered or appreciated.
Regarding estimates of cost: Other things being equal they will carry weight and conviction in proportion as they show evidence of having been formed after careful analysis; i.e., a reasonable determination of quantities based upon some survey and plan, and a subsequent procedure as outlined for contractor's estimate (of cost) No. 5. Thus a mere statement of 100,000 cu. yd. of masonry at $4.50, $450,000, while possibly a very excellent guess is not nearly as valuable and convincing as a plan or profile from which the quantity can be derived, accompanied by a tabulation of all the items entering into the cost, with a sum of $450,000.
The following tables, diagrams and data may be of some assistance in making up any of the above described estimates although they should be used only with some caution and an appreciation of their limits as to accuracy and consequent applicability for the particular estimate. The partial list of existing dams, with dimensions, quantities of masonry, cost and some accompanying pertinent notes, may (aside from its interest) be taken as a very rough indication of what another dam may cost if due regard is given as to whether the particular circumstances of the cases are comparable. Such particular circumstances are location, size, accessibility, price and quality of labor, cost of cement, amount of excavation and refill involved, amount expended in beautifying the structure and surroundings, etc. Obviously the length and maximum height as given in the table is only a very crude indication of the amount of masonry involved. For that reason, therefore, it would be much preferable to construct a profile of the dam and from the diagrams on pages 194 to 196 arrive at some number of cu. yd. as a basis for comparison. However, such analysis of and comparison with the table can at best furnish only a rough guide toward intelligent guess.
For purposes of estimates similar to Nos. 2 and 3 previously described, it would be necessary to have a fairly accurate profile across the valley or canyon at the dam-site, together with a fair indication from borings, test pits or otherwise, of the location of the rock surface; also some opinion as to depth to which it will be necessary to go into the rock for a foundation. With such information it should be sufficiently accurate to obtain cu. yd. of excavation and masonry from the diagrams; they are constructed from acceptable masonry sections, and the possible error should be much within that of the then available data. When, however, the project has reached a stage to warrant special studies and designs to meet all the particular conditions, much more accurate and detailed data in the way of surveys and borings will be at hand. Such diagrams will then be superseded by sections of the site and of the proposed structure.
Fig. 40. Curve showing amount of masonry per linear foot.