Report

HYDROGRAPHY.

Like the preceding years since Gatun Lake has been an actual body of water (1911 to date) the yield of the watershed has more than been sufficient for the requirements necessary to operate the canal. The total yield in 1916 was 10 per cent above the six-year normal (1911 to 1916, inclusive), or 6,684 cubic feet per second against a normal of 6,092 cubic feet per second. As shown on plate No. 12, the relative proportions of various sources of inflow and the disposition of the same for the calendar year 1916 was as follows:

Total yield (100 per cent).

Net yield (89 per cent).

Land area yield (83 per cent).

Spillway waste (67 per cent).

Yield from rain or lake surface (17 per cent).
Operative and useful losses (21 per cent) –
Evaporation of lake (11 per cent)---

Billion cubic feet. 211. 71 187.98 175. 03 142.59 36.69

44. 44

23.73

The Gatun Lake total yield for the dry season 1917 (January to April, inclusive), was 35 per cent below the seven-year dry season normal, or 1,348 cubic feet per second against an average yield of 2,076 cubic feet per second. Only once since the formation of Gatun Lake has the dry-season yield been below that of 1917. The yield in 1912 was 892 cubic feet per second.

While the lake fell steadily during the dry season from elevation +86.70 to +83.14, equivalent to a loss in storage of 16.14 billion cubic feet, there was still sufficient water to have furnished 11.7 additional lockages per day without cross filling in addition to the 5.5 lockages which actually occurred without lowering the lake below +81 feet assuming 7 million cubic feet per lockage or to have made 27.5 lockages per day and have the lake level 79 feet, which would give a minimum depth in the completed channel of 39 feet. The principal source of Gatun Lake watershed dry-season supply is the Chagres River above Alhajuela. The run-off from this section during the dry season of 1917 was 49 per cent below its average yield, or 686 cubic feet per second against a 16-year dry-season normal of 1,343 cubic feet per second. Table 14 gives the monthly maximum, minimum, and mean discharge of Alhajuela for 1916; while Plate No. 13 shows graphically the average monthly discharge for Alhajuela.

Tables Nos. 8 and 9 give the hydrology of Gatun Lake watershed for the year 1916, and the dry season 1917. Likewise Tables Nos. 10 and 11 cover Miraflores Lake watershed. Table No. 17 gives the monthly Gatun Lake, Miraflores Lake, and Chagres River heights for the year 1916. Table No. 15 gives the run-off data for the Gatun Lake watershed. There were lockages as follows in 1916 and 1917:

Plate No. 14 gives a graphical chart of the operation disposal of the total yield of Gatun Lake watershed for 1916, and dry season of 1917. Plate No. 15 gives a graphical chart of the Gatun Lake total yield massed for the period 1911 to 1916 inclusive, and the dry season 1917, while Plate No. 16 gives the average monthly total yield for the same period.

There were no large freshets during the year 1916, although the 14 freshets, with a rise of over 5 feet at Vigia, were well distributed throughout the year. Data on the principal freshets are given in Table No. 16.

Fifty-eight current meter measurements were made in the Chagres River au the Calle Larga gauging station during 1916, and 35 in 1917, up to July 1, covering elevation 110.80 to 95.97, inclusive. Ten gaugings were made in 1916, and 5 in 1917, at Dos Bocas (the forks of the Chagres), covering the discharges of the La Puente, the Pequeni, and the Chagres branches. The Calle Larga cross section has remained practically unchanged during the past year.

Tables Nos. 12 and 13 give the hydrology of the Chagres for 1916, and the dry season 1917. Plate No. 17 gives a graphical chart of the massed curves of discharge at Alhajuela for the current and extreme years.

Alhajuela and Vigia have been continued as floor warning stations.

The following plates and tables accompany this report:

Plate No. 12. Gatun Lake yields, storage and losses massed.

Plate No. 13. Alhajuela average monthly discharges.

Plate No. 14. Operating uses of Gatun Lake.

Plate No. 15. Total yield for Gatun Lake massed.

Plate No. 16. Total yield for Gatun Lake.

Plate No. 17. Alhajuela discharge mass curves.

Plate No. 18. Alhajuela discharge duration curves.

Table No. 8. Hydrology of Gatun Lake watershed, 1916.

Table No. 9. Hydrology of Gatun Lake watershed, dry season 1917.
Table No. 10. Hydrology of Miraflores Lake watershed, 1916.

Table No. 11. Hydrology of Miraflores Lake watershed, dry season 1917.
Table No. 12. Hydrology of Chagres River, 1916.