Welcome to Manuels River!

Manuels River Natural Heritage Society

The Manuels River has a substantial natural watershed area of 75.4 square kilometers. This watershed included two rather large water bodies; Paddy's Pond and Thomas Pond in addition to a number of smaller ponds and gullies. However, two phases of water diversion have reduced the present day watershed area to between 10 and 15 square kilometers, depending on the source of information used. Representatives of the (Newfoundland) Department of Environment and Lands, Water Resources Division, and Newfoundland Power have estimated the present day watershed at about 10 square kilometers, whereas direct examination of the topographic maps and charts indicates an area closer to 15 square kilometers. In any event the watershed of the existing Manuels River is but a shadow of the original area (between 13 and 20%).

In 1932, the flow of water from Paddy's Pond was entirely diverted into the drainage basin for the Topsail hydroelectric development. Prior to this time, Paddy's Pond had drained into both the Manuels River and Topsail systems (the proportions of flow are unknown). This initial diversion probably did not have a major impact on the Manuels River, since the drainage area of Paddy's Pond is relatively small, at 11.4 square kilometers. However, in 1956, dams were constructed at the point where Thomas Pond flowed into the Manuels River. A ditch was constructed to divert flow into Paddy's Pond, and thereby into the Topsail hydroelectric development. This had a major impact on the Manuels River, since Thomas Pond, with a watershed of approximately 45 square kilometers, formed much of the headwaters of the Manuels River system.

Today, the diverted watershed area still has some impact upon the Manuels River. During times of high run-off, usually in the spring, high water levels in Thomas and Paddy's Ponds can result in water spilling over the dams and entering the Manuels River system as it had originally.

The original watershed area for the Manuels River extended over 75.4 square kilometers, as estimated by the Water Resources Division of the Newfoundland Department of Environment and Lands. The Fisheries and marine service of Environment Canada have estimated the area at 68.1 square kilometers, reflecting the imprecise nature of watershed boundaries, particularly in the region of Paddy's Pond. The mean width of the watershed was calculated by Environment Canada at 4 kilometers, with an axial length of 17.5 kilometers. The highest point of elevation on the natural watershed is 802 meters, to the northeast of Paddy's Pond. However, the highest point of elevation on the present day watershed is approximately 700 meters, and occurs on its western margin.

Of the 75.4 square kilometers of the original watershed area, approximately 6.5 square kilometers consists of ponds and swamps. Forests comprise 56.7 square kilometers. The remaining 12.2 square kilometers consists of either barren or unclassified land. Separate measurements have not been made for the present day watershed. An examination of topographic charts indicates that the area of ponds relative to total watershed area is lower in the present day watershed than in the original. This means that the precipitation induced water flow in the Manuels River now has little opportunity for collection in any water basin - pond, lake or gully. Consequently, the flow is not modulated by these collection basins and runs rather rapidly through the river system following the precipitation. Swamps and bogs are the only present water holding mechanism and play a larger role in the present day watershed, relative to ponds.

Values for annual precipitation can theoretically be extrapolated from other areas of the northeast Avalon Peninsula to allow for calculation of flow rates within Manuels River. Similarly, monthly records for precipitation and flow rates from other locations can be used to provide indications of short term variability in the Manuels River flow. These calculations require a specified drainage area (chosen in this case to be 15 square kilometers). However, it is crucial to note that the periodic spillage of water from the Topsail watershed into the Manuels River has the effect of substantially enlarging the effective watershed. During periods of water abundance in spring and occasionally late autumn, the flow from this larger effective is evident and consequently, the quantities presented below are minimal and numbers as they are based solely on the diminished 15 square kilometer watershed area.

Based upon data from the Northeast Pond River watershed, northeast of Portugal Cove and from Seal Cove, Conception Bay, the mean annual precipitation in the region is on the order of 1300 mm. Of this, approximately 23% is lost to evapo-transpiration (direct evaporation and water transpired by plants). The remaining 77% (-1000 mm) of the annual precipitation constitutes water run-off. Of this 1000 mm, approximately 75% (750 mm) is in the form of surface run-off, and 25% (250 mm) is in the form of baseflow, or groundwater transport. Groundwater remains in the system, and theoretically becomes part of the stream outflow. Groundwater flow into a stream system increases in importance during periods of low precipitation, and therefore should theoretically serve to smooth out the flow rates over time.

The actual relationship of groundwater and surface flow relative to a particular stream system will depend on local hydrologic conditions and surveys of the literature available indicate that this work has not been conducted. Definition and assessment of these local hydrologic conditions would require significant field research effort.

Assuming a run-off/precipitation ratio of 0.77 (evapo-transpiration removing 23% of the 1300 mm annual precipitation) the annual run-off for the region is on the order of 1000 mm. This thickness of water, over 15 square kilometers (15,000,000 square meters) translates to 15,000,000 cubic meters of water theoretically discharged over a one-year period. This computation provides an averaged flow rate of 0.476 cubic meters per second. Using 10 square kilometers as the area of the watershed for the Manuels River yields an average value of 0.317 cubic meters per second. These calculations are extremely simplified, and are intended to indicate a scale of flow (averaged over a year) as opposed to an accurate mean value. The reality of the situation is that, as with most river systems, there is considerable seasonal variation both in precipitation and runoff water flow within the Manuels River basin. The lack of data specific to the Manuels River system is problematic, since precipitation and run-off data from around the Avalon Peninsula display a substantial amount of variability even from river to river. However, the addition of spillage into the system from the Topsail hydroelectric watershed is such a large factor in comparison to any local variability in precipitation volume, that it is the dominant factor in predicting seasonal flow patterns in the Manuels River.

The accompanying data illustrates the highly variable nature of the spillage flow. March and April are the months in which spillage from the Thomas Pond, and to some degree from the Paddy's Pond reservoirs generally occurs. Averaged monthly flow rates of up to 7.5 cubic meters per second have resulted from such events, with potential peak flow rates being much higher (perhaps 2 to 4 times), dependent on the flow duration. In April of 1987, almost 20,000,000 cubic meters of water spilled over the dams. This monthly volume exceeds the calculated yearly discharge volume of the Manuels River which is provided by the present day watershed alone, which is the singular most important parameter affecting the enormously variable seasonal volumes of flow down the Manuels River. It is also obvious from examining the spillage data that the volume is highly variable from year-to-year.

The following are representative yearly of volumetric totals of water accumulation and spillage for the original Manuels River watershed:

Obviously, in some years the spillage from the former watershed has had a dramatic impact upon the water flows of the Manuels River, whereas in other years the effects have been negligible. Since the data presented above covers only a period of five years, it is possible indeed probable that even larger spills have occurred in the past. It is therefore important to realize that the flow of the Manuels River is prone to increasing by one, if not two, orders of magnitude - 10 to 100 times its average flow.

The spillage data, combined with monthly precipitation data for the Northeast Pond River, indicate that the greatest run-off can be expected during the spring months of March, April, may and June, with the potential for high water levels in early winter. The lowest levels occur during the summer and early Autumn months of July, August and September.