Snow as part of the drainage system

Snow as part of the drainage system

Seasonal water supply management from crest to trough

Snow in a mountain catchment is more than just winter precipitation. It's a temporary natural reservoir that accumulates water during cold periods and gradually releases it during thaws and spring melt.

It is snow that largely determines:

spring feeding of rivers;

humidity of mountain soils;

groundwater restoration;

work of springs;

beginning of the growing season;

summer water supply;

probability of floods;

slope stability;

the state of swamps, meadows and floodplains.

Mountain snowfields and snow cover actually act as natural reservoirs, storing cold-season precipitation until warmer weather sets in.

The main principle of the project:

Snow must not only be retained, but also properly distributed across the catchment area, controlling the location of its accumulation, the rate of melting, and the direction of meltwater.

1. Snow as a seasonal reservoir

The amount of water in a snow cover cannot be determined solely by its height.

The same thickness of snow can contain completely different amounts of water:

dry fresh snow has a low density;

compacted snow contains more water;

wet spring snow can be very heavy;

The ice crust barely shows the actual water supply visually.

Therefore, the main hydrological indicator becomesSnow Water Equivalent (SWE).

SWE shows the thickness of the liquid water layer that would form if the snowpack completely melted.

Simplified calculation:

SWE = snow depth × relative snow density

For example, a snow layer 1 meter high with an average density of 0.30 contains approximately 300 millimeters of water.

For a catchment, it is not the average snow depth that is important, but the overall SWE map by elevation, slopes, hollows, forests and open areas.

2. The path of snow in the mountain system

Snow goes through several successive stages:

formation of sediments;

loss;

wind transfer;

accumulation;

compaction;

partial melting;

refreezing;

saturation of the snow layer with water;

final melting;

water penetration into the soil;

surface runoff;

feeding of springs and riverbeds.

At each stage, water can change its path.

Snowfall on one slope can be carried by wind across the watershed and effectively replenish the adjacent basin. Therefore, the winter hydrological watershed does not always completely coincide with the topographic ridgeline.

3. Spatial distribution of snow

Snow in the mountains is distributed extremely unevenly.

Its accumulation is influenced by:

height;

temperature;

wind direction;

comb shape;

slope exposure;

steepness;

solar radiation;

vegetation;

stone ledges;

roads;

artificial fences;

avalanche transfer.

Blowing zones

Usually found:

on open peaks;

sharp ridges;

convex areas;

windward slopes;

near wind accelerators.

In such places, snow may fall, but almost immediately it is carried further.

Accumulation zones

The following are most often formed:

behind the ridge;

in saddles;

in the upper hollows;

behind the bushes;

near the forest edge;

behind roads and embankments;

in leeward pockets.

Not all accumulation zones can be considered useful. A deep snow pocket can:

overload the slope;

form an avalanche;

flood the road during melting;

oversaturate the landslide soil;

delay the onset of vegetation;

damage plants.

4. Snow management tasks

The DREVO system must:

keep some of the snow at upper levels;

prevent complete blowout;

distribute snow in a mosaic pattern;

avoid dangerous large drifts;

slow down the spring melting;

direct melt water to stable areas;

increase infiltration;

reduce the peak of spring runoff;

maintain springs;

do not create an avalanche hazard;

maintain roads and infrastructure.

Snow retention cannot be separated from melt water calculation.

Each new area of ​​snow accumulation signifies a future local water source.

5. Snow on ridges and peaks

At the ridge line itself, the task is not to create the maximum thickness of snow, but to reduce its complete blowing out.

Suitable elements:

low turf grasses;

creeping shrubs;

mosaic plant islands;

low stone lines;

semi-permeable snow-retaining screens;

rough microrelief.

High, dense barriers on the ridge can form:

large drift;

dangerous snow cornice;

severe turbulence;

a sharp transfer of snow into a leeward hollow.

Therefore, the upper zone should retain snow gradually.

6. Living snow-retaining strips

Shrubs and trees can act as living snow fences.

They reduce wind speed, causing the transported snow to settle on the leeward side. Such living snow barriers are specifically used to control the formation of snowdrifts.

But for mountain watersheds they require careful design.

The correct live strip

It should be:

semipermeable;

multi-tiered;

consisting of flexible species;

located below the critical ridge line;

remote from the road;

torn into separate sections;

consistent with melt water paths.

Wrong lane

A solid, dense wall is capable of:

cover the road with snow;

form an avalanche pocket;

accumulate an excessive volume of water;

hold snow over an unstable slope;

lead to massive damage to plants.

7. Artificial snow-retaining elements

During the transition period the following apply:

wooden gratings;

semi-permeable meshes;

stone ridges;

low wicker barriers;

snow shields;

small earthen forms.

They are installed not where it is necessary to stop the snow, but where it is necessary to ensure its safe fall.

Before installation, determine:

direction of winter winds;

estimated length of snow plume;

maximum drift depth;

water equivalent of future accumulation;

the path of spring water;

condition of the lower slope;

presence of roads and buildings.

A structure that retains snow well can be hydrologically dangerous if there is no meltwater collection system below.

8. Mosaic snow retention

Instead of one large storage facility, a network of small snow pockets is created.

They are located:

behind low bushy islands;

near stone lines;

on wide, stable areas;

in small natural depressions;

above infiltration zones;

away from avalanche paths.

Advantages of the mosaic system:

water is distributed over a large area;

the maximum snow depth decreases;

melting does not start simultaneously;

the flood peak is decreasing;

the risk of avalanches is reduced;

different plant communities are supported.

9. Impact of vegetation

Vegetation at the same time:

intercepts falling snow;

changes wind speed;

forms drifts;

shades the surface;

reduces the rate of melting;

directs melt water to the roots;

prevents erosion.

Open area

In the open area:

snow is carried more strongly by the wind;

heats up faster in the sun;

may melt quickly;

more susceptible to ice crust formation.

Shrubs

Shrubs:

retain snow well;

form small moist islands;

protect young plants;

may be damaged by heavy wet snow.

Forest

Forest:

intercepts part of the snow with its crowns;

changes its distribution;

shades the snow cover;

may slow down melting;

creates a complex mosaic of open and closed zones.

A dense forest does not always increase the available water supply: some snow remains on the tree crowns and can evaporate or sublimate before reaching the ground.

10. Solar exposure

The rate of melting depends strongly on the slope orientation.

In the Northern Hemisphere:

southern slopes usually receive more solar energy;

northern ones retain snow longer;

eastern ones heat up faster in the morning;

Westerners receive strong afternoon heating.

But the real picture also depends on:

cloudiness;

winds;

shading;

heights;

dust on the snow;

vegetation;

local relief.

The design must distribute the snow so that the entire supply does not melt at once.

11. Dust and snow pollution

Dark particles reduce the reflectivity of the snow surface and accelerate its heating.

Sources may be:

bare soil;

road dust;

sandstorms;

fires;

industry;

construction work;

ash;

slope erosion.

Therefore, protecting the soil from wind erosion simultaneously helps preserve snow longer.

Snow near roads may also contain:

salt;

fuel;

tire particles;

heavy metals;

garbage.

Such meltwater cannot be automatically directed to spring areas or drinking water catchments without a pollution assessment.

12. Compaction and ice layers

During the winter, snow changes structure.

The following can be formed in it:

dense wind slabs;

ice crusts;

loose weak layers;

water-saturated horizons;

deep hoar frost;

layers of dust.

These layers affect:

water flow rate;

stability of snow cover;

probability of avalanche;

the moment the runoff begins;

the ability of snow to temporarily retain rainwater.

An ice crust on the soil surface can impede infiltration. In this case, meltwater will flow along the surface even in areas where the soil normally absorbs precipitation well.

13. Frozen ground

The behavior of melt water depends not only on the snow, but also on the condition of the soil underneath it.

There are three possible main states:

Unfrozen soil

Water can gradually penetrate into the soil.

Partially frozen soil

Infiltration occurs unevenly through cracks and thawed areas.

Deeply frozen soil

Most of the melt water turns into surface runoff.

The combination is especially dangerous:

large snow reserves;

sudden warming;

rain;

frozen soil;

ice-blocked riverbeds.

14. Spring melt

Melting is determined not only by air temperature.

It is influenced by:

solar radiation;

cloudiness;

humidity;

wind speed;

warm rain;

soil temperature;

vegetation;

dust;

overnight refreezing.

Gradual daytime melting followed by nighttime freezing usually creates a more extended release of water.

A warm, cloudy night, strong winds and rain can cause continuous melting without stopping overnight.

15. Rain on snow

Scenario rain-on-snowis one of the most dangerous for mountain watersheds.

During such an event:

rain falls on the snow cover;

warm, moist air transfers additional energy to the snow;

the snow begins to melt quickly;

rain and melt water combine;

the snow layer becomes saturated;

water comes to the surface or into the riverbeds;

the flood flow increases sharply.

Heavy rain on melting snow cover can create flash floods, especially when snowpack is deep and soil moisture is high.

The calculation takes into account:

SWE reserve before rainfall;

air temperature;

rain temperature;

duration of precipitation;

wind speed;

air humidity;

snow conditions;

degree of soil saturation;

presence of ice crust;

capacity of the channels.

16. Critical scenarios

For each snow catchment, at least the following situations are modeled.

Scenario 1. Gradual spring melting

Basic operating mode.

Scenario 2. Sharp warming

Rapid melting at all altitude levels.

Scenario 3. Warm wind

Accelerated melting and sublimation.

Scenario 4. Rain on snow

Summation of rain and snow runoff.

Scenario 5. Rain on snow on frozen ground

Minimal infiltration and high surface runoff.

Scenario 6. Melting after an abnormally snowy winter

Large total water supply.

Scenario 7. Melting after a fire

Less vegetation, more dust and faster runoff.

Scenario 8. Melting with ice jams

Blocking of bridges and riverbeds.

Scenario 9. Melting with an avalanche

A sudden movement of snow and wood into the lower part of the pool.

17. Avalanches as a means of transporting water

An avalanche isn't just a dangerous movement of snow. It also redistributes water within a drainage basin.

Avalanche is capable of:

remove snow from the upper slope;

accumulate it in the valley;

break the forest;

block the channel;

create a temporary snow and ice dam;

delay melting deep in the rubble;

cause a late local flood.

Avalanche snow can persist significantly longer than normal snow cover due to its greater thickness and density.

Therefore, avalanche cones are included in the water balance of the basin.

18. Snow cornices

Cornices are formed on the leeward edges of ridges.

They are dangerous because:

may collapse suddenly;

initiate an avalanche;

change the distribution of snow;

create a load on the edge of the ridge;

threaten paths and roads;

After a collapse, the snow is concentrated in one depression.

The following items must not be placed on potential cornice areas:

roads;

observation decks;

buildings;

reservoirs;

important sensors;

high snow-retaining strips without calculation.

19. Ice jams

In winter and spring, ice can cover:

streams;

bridges;

pipes;

narrow gorges;

road ditches.

After the blockage is broken, the accumulated water forms a sharp wave.

Therefore it is necessary:

maintain sufficient channel width;

avoid small pipes;

control narrow passages;

install level gauges;

provide a bypass route for water;

clear critical points before active melting begins.

20. Meltwater cascade

Melt water must pass through a sequential system.

The first level is snow cover

Temporary water retention.

The second level is plant litter

Slowing down and filtering.

The third level is soil

Groundwater infiltration and recharge.

The fourth level is micro-depressions.

Short-term accumulation.

Fifth level - upper streams

Controlled runoff collection.

The sixth level is the slope terraces.

Slowing down and redistributing.

The seventh level is valleys and floodplains.

Taking in excess water.

A high-level error should not be immediately propagated to the low-level.

21. Snow and spring feeding

Melt water is especially important for springs if:

the snow melts slowly;

the soil is not completely frozen;

there are permeable geological layers;

there is no rapid surface drainage;

the upper zone is not destroyed by roads;

water is not transferred to the neighboring pool.

To restore a spring, it is necessary to take into account not only summer rains, but also the winter area of ​​its snow supply.

Sometimes the spring catchment area is located significantly higher and away from the water outlet itself.

22. Snow and swamps

Mountain swamps, wet meadows and peat areas can absorb meltwater and release it gradually.

They:

reduce the flood peak;

maintain summer humidity;

filter water;

feed the streams;

create an environment for rare species.

But they cannot be used as an infinite storage device.

A completely saturated swamp during rain and snow is almost unable to absorb additional water.

23. Snow and roads

Ridge and slope roads change:

snow transfer;

drift position;

direction of melt water;

freezing depth;

ice formation;

watershed boundaries.

A road embankment can become a snow barrier, and a ditch can become a channel for melt water.

It is necessary to determine in advance:

where the skid is formed;

where the snow will be cleared;

where the removed snow is stored;

where will the melt water go;

is the snow contaminated with salt and fuel?

whether the culverts are blocked.

It is prohibited to dump road snow directly into streams and spring areas.

24. Controlled extension of snow cover

In certain areas it is beneficial to keep snow longer.

This is achieved through:

shading by shrubs;

northern exposure;

preservation of forest islands;

protection from dry wind;

reduction of dust pollution;

mosaic accumulation;

protection of snow pockets from trampling.

This approach allows for the prolongation of water flow into the soil.

However, it is dangerous to hold snow over landslide areas, roads or buildings.

25. Accelerated safe melting

Sometimes, on the contrary, it is necessary to reduce the dangerous snow reserve.

This may be required:

over critical infrastructure;

near the avalanche pocket;

before heavy rain is forecast;

in the ice jam zone;

near an unstable embankment.

Such measures require a professional solution.

It is not allowed to go uncontrolled:

darken the snow;

destroy cornices;

redirect melt water;

mechanically dump large masses;

use chemical reagents in natural watersheds.

26. Snow cover monitoring

The surveillance network includes:

snow measuring rods;

automatic height sensors;

snow pillows;

manual snow routes;

SWE dimension;

weather stations;

temperature profiles;

snow moisture sensors;

cameras;

satellite images;

radar;

LiDAR;

drones;

soil temperature sensors;

stream flow meters.

One measurement point does not represent the entire mountain basin.

Stations required:

on the ridge;

on the windward slope;

on the leeward slope;

in the forest;

in an open area;

in the hollow;

near the avalanche cone;

at different heights.

National snow monitoring systems also use a combination of ground stations, models, and SWE maps to estimate water storage at the basin level.

27. DREVO Snow Digital Twin

The digital twin snow module contains:

snowfall map;

snow depth;

SWE;

density;

temperature;

ice layers;

humidity;

wind direction;

blowing zones;

accumulation zones;

cornices;

avalanche paths;

frozen soil;

melt forecast;

rain snow forecast;

state of riverbeds;

risk of traffic jams;

expected hydrograph.

The model should answer the questions:

how much water is in the snow;

where exactly is it located;

when the melting starts;

which areas will start to melt at the same time;

how much water will be absorbed;

how much will end up in the riverbeds;

where the maximum flow will occur;

which lowlands may be flooded.

28. Early warning system

Green level

Snow cover is stable, melting is insignificant.

Yellow level

Active daytime melting begins and the soil becomes moist.

Orange level

A sharp warming or rain and snow are expected.

Red level

High probability of flood, avalanche, ice jam or landslide.

Black level

An actual large avalanche, a breakthrough of a jam, or a rapid flood.

The warning must take into account not only the precipitation forecast, but also the current SWE, soil conditions and the filling of underlying water bodies.

29. Climate change

Snow catchments are becoming less predictable.

Possible:

later snow formation;

early melting;

rising snow line;

more winter rains;

less stable snow cover;

more frequent rain-on-snow events;

sharp transitions from frost to warmth;

reduction of summer river feed.

WMO notes the reduction in snow and ice cover in many mountain regions and its impact on water availability and river flow.

Therefore, it is impossible to design a system based only on historical average data.

Scripts needed:

little snow in winter;

abnormally snowy winter;

warm winter with rain;

early melting;

late snowfall after the beginning of the growing season;

several cycles of freezing and thawing.

30. What not to do

In a snow catchment area it is prohibited to:

estimate water reserves only by snow depth;

create one huge snow storage facility;

install snow-retaining strips without calculating melt water;

to hold snow over a landslide slope;

block avalanche paths with buildings;

place the road under the eaves;

use small pipes in areas of ice jams;

dump contaminated road snow into streams;

ignore soil freezing;

consider the leeward side safe;

design only based on average snowfall;

forget about rain and snow;

direct all spring runoff into one channel.

31. Design sequence

Step 1. Mapping

The zones of fallout, blowout, accumulation, avalanches and melting are determined.

Stage 2. Measuring snow reserves

Height, density and SWE are estimated.

Step 3. Calculating wind transport

The actual redistribution of snow between slopes is determined.

Stage 4. Soil analysis

Frost penetration, infiltration and slope stability are checked.

Stage 5. Accumulation design

Safe mosaic snow pockets are created.

Stage 6. Design of melt runoff

The path of water after melting is determined.

Step 7. Calculation of extreme events

Warming, sleet, avalanches and ice jams are being checked.

Stage 8. Monitoring

The system monitors snow throughout the winter.

Stage 9. Adaptive control

After each season, accumulation and melt runoff maps are updated.

The final principle

Snow is the upper seasonal reservoir of the entire mountain catchment area.

It must be considered simultaneously as:

water supply;

soil protection;

source of spring nutrition;

wind-driven mass;

load on plants and structures;

avalanche factor;

flood source;

spring power supply element;

part of climate resilience.

A properly organized snow system:

distributes snow over stable areas;

reduces total blowout;

does not create dangerous drifts;

prolongs water supply;

maintains soil and springs;

reduces the spring flood peak;

safely passes extreme excess.

Snow management ends not at the moment of its fall, but only when the meltwater has safely penetrated the soil, replenished underground horizons, or passed through the catchment area to the river and lowlands.