PAGE .............................................................. 150 ▼ T8.1 FRESHWATER HYDROLOGY ○ Nova Scotia has no shortage of fresh water. The total Limnology and hydrogeology are specialized mean precipitation is fairly high: approximately 1300 branches of hydrology. Limnology is the study of sur- mm as compared to 800–950 mm in central Ontario face freshwater environments and deals with the rela- and 300–400 mm in southern Saskatchewan. Fre- tionships between physical, chemical, and biological quent coastal fog, cloudy days and cool summers components. Hydrogeology is the study of ground- combine to moderate evapotranspiration. The re- water, emphasizing its chemistry, migration and rela- sult is a humid, modified-continental climate with a tion to the geological environment.1 moisture surplus. Large areas of impermeable rock and thin soils and the effect of glaciation have influ- THE HYDROLOGIC CYCLE enced surface drainage, resulting in a multitude of bogs, small lakes and a dense network of small The continuous process involving the circulation of streams. Groundwater quality and quantity vary ac- water between the atmosphere, the ocean and the cording to the type of geology in different parts of the land is called the hydrologic cycle (see Figure T8.1.1). province. The following topics describe the cycle of Solar radiation and gravity are the driving forces that water and the various environments and forms in “run” the cycle. which it manifests itself. Fresh water as a resource is As water vapour cools, condensation occurs and discussed in T12.8. clouds form. When rain or snow falls over land, a number of things can happen to the precipitation: ○○○○○○○○ some of it runs off the land surface to collect in catchment basins, some is returned directly to the Hydrology is the study of water in all its forms and atmosphere by evaporation and by transpiration T8.1 its interactions with the land areas of the earth. It in plants (evapotranspiration), and some perco- Freshwater deals with snow and ice on the land, moisture in the lates underground (infiltration) to become Hydrology air, liquid water in lakes and rivers, as well as water groundwater. occurring below the ground in the spaces between Underground formations that readily give up their soil and rock, and within the soil. water for wells are called aquifers (see T8.2). The Solar Radiation Atmospheric Moisture Precipitation (Rain and Snow) Stream Evaporation Evaporation Falls & Transpiration Surface Runoff Percolation Lake River Estuary Ocean Bedrock Groundwater Flow Aquifer in Sedimentary Rocks Figure T8.1.1: The hydrologic cycle. Natural History of Nova Scotia, Volume I: Topics © Nova Scotia Museum of Natural History .............................................................. PAGE 151 ▼ upper water level in an aquifer is known as the water WATERSHEDS table. Water is continuously flowing underground and can move back to the surface by capillary action A watershed, or drainage basin, refers to the area of or be transported horizontally by subsurface flow, land from which surface water drains into a com- until it reaches a surface water system.2 mon lake or river system or directly into the ocean. Nova Scotia’s cool climatic conditions produce a The flow is generally inwards and downwards, ac- cycle where precipitation exceeds evapo- cording to the topography of the surrounding land- transpiration. Due to the high rate of annual precipi- scape. The boundaries of a watershed area are known tation, rivers, lakes and aquifers are replenished or as a drainage divide: precipitation falling on oppo- recharged, although the rate varies, depending on site sides of a divide falls into different watersheds. the amount of precipitation, the type of soil, the The underlying geology and type and depth of topography and the geology of the area. In areas surficial overburden of every drainage basin are dominated by rocky land surfaces, such as in south- major factors in determining its characteristic drain- western Nova Scotia (Regions 400 and 800), the age pattern (see T3.2). The watershed has become amount of runoff is very high and, subsequently, the unit used by water-resource planners and man- groundwater recharge is slow. Where more porous agers in dealing with developments within an area soils are found, such as in the Carboniferous Low- that may have an impact on water quality and quan- lands (Region 500), infiltration is much greater, and tity. Any activities that occur in the upper portions of thus groundwater is higher. a watershed will have an impact on water quality in downstream areas. Figure T8.1.2: Locations of primary watersheds in Nova Scotia. © Nova Scotia Museum of Natural History Topics: Natural History of Nova Scotia, Volume I PAGE .............................................................. 152 ▼ WATERSHED # MAJOR RIVERS TOTAL AREA (km2) Lrand WlateTota 1nDAM0etegha5174161 1rDBS9issibooandBea193478142 1sDC A9nnapoli202079227 1uDD G6asperea183155137 1xDE S6t.Croi113068136 1kDF K6ennetcoo19511 112 1eDGS0hubenacadieandStewiack235474261 1tDHS4almonandDeber14816116 1yDJ E0conom7339 79 1oDK P6arrsbor8285 85 1tDLK5elley,MaccanandHeber19429130 1sDMT5idnishandShinimica449747 1eDNP5hilipandWallac194714149 1nDO J1oh16711 111 1)DPE0ast,Middle,West(Pictou17719119 1hDQ F5renc7163 73 1)DRS8outhandWest(Antigonish897990 1eDS T0racadi5668 58 1tEA T2uske1498179217 1eEBB3arringtonandClyd192472132 1nECR0osewayandSableandJorda143585143 1yED M0erse2969303303 1yEEH5erringCoveandMedwa1684126201 1eEF L1aHav196180170 T8.1 1dEG G2ol97759102 Freshwater Hydrology 1nEHE5astandIndia6996576 1eEJ S4ackvill9127699 1tEKM6usquodoboi133199140 1rEL T4angie917161108 1)EME4ast(SheetHarbour9417898 1bEN L6iscom161362120 1sEO S5t.Mary'135049154 1rEPC0ountryHarbou5851956 1)EQN9ewHbr./Salmon(Guys.100179108 1sERC7lamHarbour/St.Franci5411253 1sFA I3nhabitant101914120 1eFB M8argare173065137 1pFC C2heticam8360 80 1eFD W7reckCov150512107 1nFE I2ndia8708 89 1eFFN4orth,BaddeckandMiddl727676 1gFG D2enysandBi7249 79 1dFH G9ran7333277 1aFJS9almonandMir2477143291 *eI5sleMadam1614 15 Table T8.1.1: Characteristics of primary watersheds in Nova Scotia. The figures were calculated by the Maritime Resource Management Service for the Nova Scotia Department of Environment in 1981. *Isle Madame is classified as a shoreline direct inflow to salt water on the 1:50 000 watershed maps for Nova Scotia. Natural History of Nova Scotia, Volume I: Topics © Nova Scotia Museum of Natural History .............................................................. PAGE 153 ▼ Most of the forty-four primary watersheds in the province are relatively small, ranging in size from Due to the Shubenacadie Canal, the Shubenacadie 151 to 3030 km2, especially those near the coastal River is Nova Scotia’s longest river. The canal cuts zone, where numerous small streams flow directly perpendicularly across a major drainage divide into the ocean.3 There are three major drainage areas and consequently water flows both north towards in Nova Scotia. One large divide runs in an east–west Cobequid Bay and south into Halifax Harbour. direction across the mainland of the province. A second divide cuts across the top of the Cobequid Hills and the Pictou/Antigonish Highlands (District 310). The Canso Strait serves as another divide by WATER BUDGET separating Cape Breton from the mainland. Figure T8.1.2 shows the distribution of the major water- Nova Scotia averages 1300 mm of precipitation annu- sheds. On Cape Breton Island, most of the water- ally; however, there are times when water levels in sheds are quite small, mainly due to the fragmented lakes and rivers are low and wells run dry. It is esti- topography and the existence of the Bras d’Or Lake mated that less than 20 per cent of the total amount of system (District 560, Unit 916). The two exceptions rain and snow seeps underground to recharge the to this are the Margaree (1375 km2) and the Salmon- water table.2 This occurrence relates directly to the Mira River system (2914 km2) amount of runoff, which has been estimated at 1018 Some of the largest watersheds are found in the mm per year (based on the average annual value for Atlantic interior (Region 400), such as the Medway, data recorded by Environment Canada).5 Runoff is 2012 km2; the LaHave, 1700 km2; and the Shube- influenced by many factors, including soil type, soil nacadie-Stewiacke River system, 2614 km2. The larg- moisture conditions, slope of the land and the amount est watershed in the province belongs to the Mersey of vegetation cover. In general, coarse soils with low to River, which drains an area of 3030 km2. A complete moderate runoff potential occur throughout the prov- list of primary watersheds is provided in Table T8.1.1. ince. The exception occurs in central and northern Primary, secondary and tertiary watersheds in Nova Nova Scotia, which have more finely textured soils Scotia have been mapped at a 1:50 000 scale. These with higher runoff potential. Runoff can be acceler- maps are available through the Nova Scotia Depart- ated by the removal of vegetation or infilling of T8.1 ment of Environment. wetlands. The accelerated runoff can in turn increase Freshwater In addition to the primary watersheds outlined erosion, leading to higher levels of sediment loading Hydrology above, Environment Canada has also divided the and turbidity within streams. Figure T8.1.3 shows the province into three separate hydrological zones.4 The mean annual runoff pattern for the province.4 criteria for making these divisions are based primarily Evapotranspiration