Watershed Hydrology - Google Sites

Watershed Hydrology - Google Sites

Conserving freshwater aquatic ecosystems requires consideration of 1. Flow regime 2. Water quality Land cover in a catchment affects both

Impacts of land-use on hydrological processes Water Cycle Human Impacts on Water Resources

Watershed land use has overarching effect on the water budget Effect of land use

Activities like clear-cut deforestation- eroded sediments, flooding downstream Poor agricultural land management activities - eutrophication and possible fish kills.

Land use Land cover: Forest Land use: Teak Plantation, Pine plantation, Protected Forest

Land use map Land use and hydrological processes Vegetation type affects infiltration and evapotranspiration

Veg type: Grasslands, forests, single species plantations, mixed species plantations, Stage of succession, agriculture

Red: Deforestation in Shillong area 2000-2012 Residential and urban influences on hydrological processes

Components of hydrological cycle Precipitation - rain, snow, fog interception Runoff

Storage Subsurface flow Evaporation - soil, plants, water surface

P = Precipitation S = Storage ET = potranspiration R =

noff(Discharge) P + (S) = ET + R Stream flow is a function of precipitation

P + (S) = ET + R Plantations and afforestation in dry areas leads to decline in annual stream

flows, due to losses from ET P + (S) = ET + R However when baseflow is compared across

watersheds, watersheds with greater forest cover have greater baseflow than deforested watersheds P + S = ET + R--------greater Forest

P + s = ET + R----------lower forest Baseflow: flow in streams when there is no rain, like in the dry season Groundwater flows underground until the

water table intersects the land surface and the flowing water becomes surface water in the form of springs, streams/rivers, lakes and wetlands. Baseflow is the continual contribution of

groundwater to rivers and is important source of flow between rainstorms. Groundwater continues to discharge as baseflow because of the new recharge of rainwater in the landscape.

Now, droughts in the worlds wettest place, Cherrapunjee, Khasi Hills, Meghalaya, India Dry season by Jan and Feb springs are drying up.

People carry water up and down hills for long distances. Causes: Deforestation -- rainwater runs off

-- soil washed off -- less soil to hold water -- soil compaction and hardening due to exposure to sun and wi

Climate change Population increase -- cement industry using limestone

Cherrapunjee High Rainfall & Rainfall intensity Low Infiltration, due to armoured substrate, lack of vegetation High Discharge/runoff, as a result of high slope

P+ S = ET

+ R Soil erosion through deforestation:

Madagascar Many aquatic macroinvertebrates Live in gaps between and under stones

Pristine streambottom lots of gaps Sediment choking gaps between stones Trees protect fishes

Riparian vegetation buffers Buffer Width depends on the amount of sediment in runoff: a function of

Slope, rainfall, soil type land cover (whether primary forest, plantation, agriculture, lack of terraces, urban)

30 m buffer width for rivers in Tanzania Rice field terraces on hillslopes in Yangshuo, China

Fluvial geomorphology, stream restoration Channelized streams for flood control, irrigation, development Negatives loss of aquatic ecosystem habitat. Changes in flow Los of streambank stability, increased erosion, flooding and bre

So stream restoration, needs fluvial geomorphology knowledge A natural stream: diverse morphology and habitats

Stream orders in a watershed Steep slopes in headwater catchments Lower elevations,

Lower slopes Streambanks and Floodplains: dynamic The end of the road.. Or stream

About two-thirds of the worlds population depends upon groundwater Groundwater resources

Better quality usually than surface water, In terms of bacteria, sediments and chemicals in developing countries. Increasing use in rural communities via Tube wells

Heavy use in irrigation and urban water supply Increasing use in bottled water too. Groundwater terminology

Aquifer capacity Sand/ limestone

Silt/loam/clay Groundwater movement slow Groundwater resources - issues

Unsustainable: Extraction GREATER THAN natural GW recharge

Falling water table -> wells run dry Deep GW extraction can mobilize arsenic (toxic)

GW quality deteriorating from leaching Forests and wetlands degrade due to lowered water table Land subsidence (eg Mexico City, Bangkok, Venice) Salt water intrusion into aquifer (Hallandale, Miami)

Groundwater overextraction Nearly a third of India is suffering from chronic water shortages, and making up for it with "the world's largest groundwater mining operation --National Geographic special report on global water issues, 2010.

http://www.nasa.gov/topics/earth/features/india_water.html Seawater intrusion Questions and discussion

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