Hydrology + Catchment Systems KWs

drainage basins

catchments delimited by the watershed

watershed

boundary separating land draining to one river/stream from land draining to adjacent rivers

interception

when rain is caught by veg/other structures before hitting the ground

infiltration

water at the surface soaks into the top layer of soil

percolation

water moves down top layer of soil and into bedrock

drainage density

how well connected river channels are

eutrophication

water body becomes overly enriched with nutrients, lessens DO

orographic rainfall

moist air from ocean is forced over mts/high ground - cools as ot ascends and condenses to form clouds and pp

common in coastal mt regions (e.g. W UK)

creates a ‘rain shadow’ in the E

convectional rainfall

sun heats ground - air warms and rises rapidly, cools as it does leading to condensation and formation of large clouds

usually short-lived but intense storms

most common year-round in tropical climates, and during hot summers in temperate reigons

frontal rainfall

two air masses w diff temps/densities meet - warm air is less dense so forced up over colder + denser mass, warm air cools + condenses creeating prolonged + steady rain

responsible for majority of UK’s winter rain

condensation nuclei

aerosols e.g. sea salt/dust which water vapour condenses around to form rain

artificially used in cloud seeding

evapotranspiration

evaporation from soil matrix + transpiration

evaporation = net balance btwn rate of vaporisation + condensation

atmospheric mixing

how well a parcel of air is able to diffuse into the surrounding atmosphere

leaf area index (LAI)

total one-sided green leaf area per unit of ground surface

throughfall

pp that falls directly through gaps in plant canopy to the forest floor

stemflow

portion of rainfall intercepted by vegetation, flows down branches + trunks, eventually soaks into soil directly around the tree base

streamflow

the continuous, concentrated flow of water within a defined channel (rivers + streams)

= combo of throughfall, GW + surface runoff making its way into the watershed’s drainage network

soil heterogeneity

horizontal -variations due to underlying geology + climate, diffs downslope

vertical - soil horizons, dep on O2/W levels, microbial/animal action → inf rate W passes through soil/stored through it

saturation

vol of pores filled w W

max amt of W soil can hold

inf by texture/structure + soil OM content

hydraulic head

measurement of the mechanical energy per unit weight of a fluid

expressed in units of length

represents height to which W would rise in a column or well

W always flows from areas of a higher hydraulic had to a lower hydraulic head (think of it in terms of a press gradient)

total porosity

total number of pores

effective porosity

proportion of spaces that are connected

how permeable the rock is/ability to allow W to flow through

water table

underground invisible boundary where soil + rock become completely saturated w W

interception loss

water sitting on canopy is directly evaporated

higher interception ratio in drier > wetter climates, greater in wetter climates + denser/taller veg

interception gain

trees intercept fog particles (‘fog drip’), ends of pine needles act as condensation nuclei so larger droplets form when fall to the ground

antecedent conditions

preceding circumstances/env factors that can lead up to/triggeer/influence an outcome

direct channel precipitation

direct input of pp into river channel - no intermediary

fastest pathway, but only a small fraction of runoff mechanisms

might become more important during storm as Q inc + ephemeral streams become activateed

ephemeral streams

short-lived water bodies - flow only during/immediately after precipitation or snowmelt

infiltration excess overland flow (IEOF)

aka Hortonian overland flow

when infiltration rate (high intensity rainfall) > infiltration capacity

e.g. w impermeable surfaces

saturation excess overland flow (SEOF)

all pore space filled (WT at the surface)

can occur even when not raining

partial contributing area concept

spatial variability of surface produces patchy runoff

variable source area concept

seasonally/over the course of a storm the area which is saturated in a catchment changes → greater SE in shallow soils/bottom of hillslope/after wet periods

Darcy’s law

fluid flow rate is directly proportional to pressure difference (hydraulic gradient) driving the flow

hydraulic conductivity

ease with which a fluid can move thorugh pore spaces or fractures

property of porous materials e.g. soil/rock

matrix/matrix flow

matrix = main structure of soil

matrix flow - main system of W flow in soil → W moves from wet to dry areas in soil, controlled by Darcy’s law

macro-pore flow

(non-Darcian)

soil pipes

> 1mm in diameter

can transport W/sed/sol through soil + bypass soil matric

rapid connectivity of water, acts as a subsurface drainage network w minimal barriers to W flow

found more commonly in peatlands + arid areas (bc of soil characteristics)

baseflow

portion of the streamflow that is sustained btwn precipitation events

seeps into streams/rivers from underground aquifers

long lag times, movement based on gravity + rate dep on darcy’s law

GW flow

dep on percolation + rock needs to be porous and permeable

aquifers - need to be porous enough to store waster + permeable enough for W to flow through in large quantities

quickflow

portion of rainfall/snowmelt that reaches a stream channel rapidly, causing river levels to spike

typically consists of surface runoff + interflow (shallow W moving quickly through the upper soil layers)

aquifers

underground layer of W-bearing permeable rock

acts as a natural underground reservoir

water balance equation

inputs - outputs = change in storage

relies on law of conservation of mass

fluvial (river) flooding

driven by rapid thaw/heavy rain - inundate FPs, usually affects large areas

pluvial (surface) flooding

periods of heavy rain overwhelm drainage systems + concreted imperm surfaces (prevents from draining away)

IEOF

flash flooding

intense rainfall + flow at high speed for a short time

IEOF

GW flooding

WT in permeable rocks rises to enter cellars/comes up above the surface

tidal (coastal) flooding

severe storms/strong winds/high tides cause large waves which break down defences + flood coastal areas

strong winds + high tides, storms

risk

potential loss in a society/community/system in a specific period of time, determined probabilistically

hazard

natural process/phenomenon which may cause soc/econ/env damage

exposure

situation of people/infra/tangible assets located in hazard-prone areas

vulnerability

conditions increasing susceptibility

floodplains

low, flat area of land next to a river/stream

naturally prone to flooding when W overflows its banks

design flood

what flood defences are designed to withstand, e.g. 1 in 100 yr event

sediment types

biological - remains of dead orgs → shells, plants, remains of framework orgs e.g. chorals

chemical - produced from chem processes e.g. salt

clastic - particles weathered/eroded from rocks, resistance to weathering → implications for transport

discharge equation

Q (cumecs) = cross-sectional area (m2) x velocity (m/s)

laminar flow

smooth, parallel layers of fluid sliding past one another w minimal mixing

lower velocity

turbulent flow

swirling eddies that rapidly mix the fluid

higher velocity

Hjulstrom curve

shows grain size + cohesion as key controls on transport

flux

rate of movement

redox potential

destabilises mineral structures + promotes weathering

DO

dissolved oxygen

BOD

biochemical oxygen demand

oxygen sag curve

shows drop + subsequent recovery of DO levels downstream from a point source of pollution e.g. sewage discharge

RDS

road deposited sediment

gully pots

kerbside drainage chambers used to collect surface runoff from roads + divert into underground sewer networks, often have sediment traps to prevent blockages further down the system

act as pollution ‘hotspots’

when flooding/heavy rain occurs, polluted sediment gets washed out into surrounding environment

first flush effect

pulse of sediment before peak discharge (+ve hysteresis)

legal vs illegal sewage discharge

legal - under heavy/prolonged rainfall where system may otherwise become overwhelmed

illegal (dry) - no rain → raw sewage enters the river w/o dilution potential

critical source area concept

not all areas of land have an equal risk of contributing pollutants

monitoring

implies repeated measurements/samples

change over time, same place

survey

measurements spread over space (but taken at the same time)

BACI

before-after-control-impact

stage

depth of the W channel

blue water

surface + freshwater

green water

embedded in evapotranspiration cycle through veg

grey water

polluted WW from urban envs (e.g. showers/laundry/etc)

black water

WW in a sanitation context

likely to contain sig pathogen burdens + OM (toilets + latrines)

ecosystem services

direct + indirect contributions of nature to human wellbeing

foundation of economy + survival

over-banking

when river discharge exceeds channel capacity, water/sed spilled onto FPs

hard engineering

use of artificial, man-made structures to control/manage natural processes inc river flow + flooding

WWNP/NFM

WWNP - working with natural processes

NFM - natural flood management

deculverting aka ‘daylighting’

process of removing artificial pipes or concrete channels that force a river/stream to flow underground

restores buried watercourses to the surface, recreating natural beds, banks, and ecological habitats

offline storage

aka off-stream storage

managing W outside the main river chnanel → W diverted to a diff area e.g. pond/wetland/reservoirs

during high flows, stored temporarily to attenuate the flood peak and then safely released back into main watercourse after the peak has passed

type of flood management

e.g. balancing lakes

swales

shallow, vegetated channel/depression in the landscape designed to manage surface runoff

used to collect/filter/slowly absorb rainwater into the ground to prevent flooding + reduce soil erosion

palaeolimnology

reconstructing past environmental/ecological conditions of inland water bodies (lakes, rivers, wetlands) by analysing sediment cores

helps to establish LT baselines for CC, eutrophication + human impact

WFD

water framework directive

introduced by the EU

RBMP

river basin management plan

part of the WFD

CSOs

combined sewage overflow

valve built into sewer system which can be opened during times of high rainfall etc to prevent sewage overflow

STWs

sewage treatment works

SUDS

sustainable urban drainage systems

uPBTs

ubiquitous, persistent, bioaccumulative and toxic substances

long-lived pollutants e.g. mercury, PFOS, etc

build up in food chain

headwater

upper reaches + source streams of a river network where surface runoff, snowmelt, or springs first accumulate into a flowing channel

represent the geographic beginning of a river and are the furthest point from its confluence w another body of water