Dam problems

[strud]

Hello all.

I am new to the world of permaculture, but in many ways have been trying to implement similar ideas already.

Since this is my first post to this forum so I should give a short introduction.

My wife & I bought a 12 acre property at Blaxlands Ridge NSW in April this year. Approx 7 acres is mostly cleared and reasonably flat (house situated on a crest) with a dam in the bottom corner on this section. Behind the dam is another 5 acres of original bushland, which is quite steep in places with a gully thru the middle.
This area has quite sandy soil and lots of sandstone near and breaching the surface.

We are currently having some problems with the dam. They are :

- Green colour with slightly sulphurous smell
- Large amount of reeds
- Large duck population (2 families of about 7)
- High evapouration rate
- poor runoff/catchment

some pics are here :

http://members.optusnet.com.au/~cstrudwicke/Blaxlands_Ridge/Property.html[url]

There has been attempts made in the past to improve the runoff to the dam, one such attempt is a long swale (?) across the sloping paddock the dam is in, which runs down to the dam.

Can anyone identify the reeds in the linked pics ?
-Are these problematic for the dam ? (They seem to be clogging it up)
-Is it worth making modifications to the swale ? ie ag pipe, plasting sheeting
- Should we grow some form of surface plant in the dam to reduce evapouration and absorb nutrient ?

Craig

[permaculture.biz]

G'day,

1. Looks like a drain not a swale. Swales don't have any fall. It may not have been compacted so operates like a swale. Compaction would help. The native catchment to the drain maybe too small. Calculate the catchment area then apply the following formula:

100 x Area (ha) x Annual Rainfall (mm) x 10% (arbitrary runoff cooefficient)

2. Reeds are good. They are there because the water has enough nutrient to feed them and the edges are quite shallow. Part of your dam's problem is that it is not deep enough. In an area with about 1800mm+ of annual evaporation you need to be at least 3m deep. Shade the dam, make it deep, keep it cool. Removing any stock access to the dam would definitely help.

3. I would excavate a small silt trap/reed bed at the end of the catchment drain. 500mm deep x 3m x 3m should do the trick. Transplant some of the lovely Juncus spp. you have in the dam and that should help with the sedimentation (turbidity) and nutrient reduction.

4. Adding bales of barley or other straw to the dam will assist with the algae issue though it is symptomatic of other aforementioned issues.

Good luck and keep talking,

Ciao

[strud]

Permaculture Biz (Darren ?)

Many thanks for the reply.

Thanks for the correction regarding the drain. Haven't got my terminology correct yet :-)

Would not running a large ag pipe increase this runoff co-efficient ?

Re making dam deeper : Are there people out there that can dredge a dam ? I guess there is a risk of going too deep and making it leaky ?

When you stated adding straw to the dam, did you mean as a buffer/filter to prevent entry of sediment ?

Craig

[gardenlen]

g'day craig,

not a very large dam, but i must suggest you go with caution if you go to improve the water holding capacity of the dam, not always advised to do that, best option another dam as you may ruin what you already have. maybe the original builder of the dam built it that size as it would fill better from the available rain run off??

the green can be fixed with a bale or 2 or barley straw.

the reeds look a bit like bull rushes, they are an advantage as are the ducks so the water quality can't be all that bad, if there is a sulphur content then that is due to the type of land you might have, dunno must be a way of getting a water sample tested for that sort of content.

looking at the land your soil looks very sandy?

the one thing i would suggest is get those trees of the dam wall, that is the first no no we where ever taught when we were looking for property, thay can and often cause the wall to fail and and have a dam burst. all you want on the dam wall is grasses and woody type weeds at best.

i would suggest that the dam is as good as it is ever going to be, but seek out a local expert as being onsite is always better than looking at pictures.

you aren't going to get any water inot that dam without rain and run off just the way it is, and at just looking at it the dam is probably holding as good a water as it can.

with 2 meters of water in the middle the dam will probably be around 4 meters deep when full, that is about average for smallish dams.

i would be making sure that any run off on the block all was directed to the dam, as well any run off from boundry roads i would try to direct as much of that as possible onto the property, also swales up high even if they are only rip swales to get water into the sub soil, this will help with the dam if the dam is actually being maintaned by a sub aquafa water level (sulphur smell?).

len

[gardenlen]

forgot to add for desilting (not necesarily deepening the dam) the dam will need to be pumped dry, so there could be a very long wait at present for rain to refill it. seek much local advice and go carefully.

len

[permaculture.biz]

G'day,

I agree with Len's points. I was remiss in suggesting that you need to seek local advice as opposed to using an internet forum as the font of appropriate advice.

Certainly deepening an existing storage by a few metres is quite doable: usually an operation carried out using an excavator. If you are struggling to fill the storage to this point then this will only be exacerbated by going deeper. Certainly Len's advice is accurate in trying to pick up runoff from any hard surfaces. As I said you need to complete a catchment analysis.

I have a problem with the application of swales as catchment devices on some sites in that they have to fill before they then flow excess into a storage. Diversion drains (falling @ >1:400) on the other hand drain lighter rainfall to dams. In events of less than 5-10mm they ostensibly operate as a swale. Diversion drains are also compacted unlike swales.

Ciao,

Daz

[strud]

Still note sure what is meant by 'addding' a bale or two of barley straw ?

[gardenlen]

ok strud,

barley straw whatever they want to call it is used to take the green algae out of ponds and dams, so whatever buy yourself some barley straw and put a bale into the dam maybe put 2 in more if you like but 1 or 2 shoulkd be heaps it will take up the algae whatever it does ok? you can of course pull the bales out once the green ahs gone and use them as mulch in yoru gardens etc.,.

and you can then leave the bales in there to break down and feed the habitat that will be in the bottom of your dam, another reason why you should consider very carefully before tampering with an exisitng dam. there is a whole lot of variables to consider before then, that is why i would suggest spending that time and money on maybe another dam right beside that one, below that one to the side but remember if one dam is going to rely on another to overflow before it will fill that may not be an advantage in our current seemingly endless climate.

len

[Paul Cereghino]

Here's my theory,

Looks like the pasture is pretty beaten and everything has been grazed. The dam gets runoff from the dam has a watershed. Like all wetlands it is a nutrient sink. Any mobile nitrogen (cow shit) in the catchement area gets carried into the pond during the rainy season. nitrogen+sunlight in water grows algae. The algae grows, takes up nitrogen from the water and carbon from the air, but than it dies. Lots of nitrogen yields lots of algae. The heaps of dead algae gets eaten by bacteria and turn it all into nutrient rich slime. The bacteria use oxygen. Oxygen diffuses through water around 1000 times slower than through air. Lickity-split the bacteria eating the dead algae use up all the oxygen in the water faster than it can be replaced, they are replaced by bacteria that are adapted to life without oxygen (anaerobic).. they use sulfer compounds (sulfate) as a substitute for the now depleted oxygen. The excrement of the anaerobic bacteria includes things like oxygen sulfide (the rotten egg smell).

Shade will reduce temperature. Colder water has the capacity to hold more dissolved oxygen. But if you have nitrogen flowing into the system, temperature alone wont help you that, as your low oxygen situation is driven by the nutrient-algae bloom. Straw has losts of carbon and little nitrogen. Bacteria eating the straw borrow nitrogen from the water, then when you pull the straw out you are exporting nitrogen, same if you were to cut and used the reeds in an upland location.

If you want to capture the nutrients before they go into the water you need to pass the water through a healthy soil with plant roots in it... either increasing water retention in your pasture soils (chisel on contour), or running the water through a treatment wetland before it gets into you storage. If you don't care that you storage is anaerobic (no fish that I know of)... then no big deal... your pump water has nutrients to boot as long as you dont clog your irrigation system.

If you don't have a shortage of storage in your pond (it never fills up). Than having it fill in with nutrient rich goo doesn't really matter, and eventually you'll get lots of rushes, and then you can use the rushes for something... and maybe harvest the nutrient goo for something else it your goo grows too deep for comfort (like your dog goes missing..). If you want a "healthy" pond... water with oxygen that supports fish... than you'll likely need shade, much much less nitrogen going in the system, and possibly aeration, and even then there may be enough nutrients in the sludge to keep algae blooms going for a while... dredging the goo may also help if your goal is to head toward low algae, higher oxygen water. Of course your climate may not support that kind of thing (ive never been to NSW) and you may only be able to get carp gulping for air near the surface in an ephemeral pond in the best of conditions. I would suggest that depth alone will not create a crystal pool.

The seasonal drawdown may create an opportunity to grow annuals in the moist sediment. Desert tribes in the SW USA used to grow wild rice in such settings.

Good luck,

[strud]

Sounds like aeration might be a good idea then ?

Easiest way to implement this for me would be to run some sort of spnkler/fountain into the dam during the evening (minimising evapouration) since we have a grunty pump down at the dam. All that would be required to do this is a programmable valve and a few nozzles.

Will put in the bales of barley straw too.

Oh by the way, is the typical bale of straw typically barley ? or will I have to specifically as for barley straw ? ( I have a bunch of 'straw' bales already but dont know what crop they came from).

[Richard on Maui]

I think Barley straw is probably a bit more expensive than your average bale which can vary a lot depending on lots of um, variables. I think the Barley is supposed to specifically promote certain bacteria that work to redress the imbalance in stinky ponds.

[gardenlen]

yes richard,

here where i am i can get sugar cane mulch bales or pasture grass hay bales for around$7AUD and barley straw comes in around $10AUD, but for getting rid of algae in a dam/pond whaever then barley does the job.

len

[Paul Cereghino]

[quote="strud"]Sounds like aeration might be a good idea then ?

Low oxygen is more of a symptom than the problem... I'd bet that nutrient management is the bigger issue. Since it doesn't sound like you are trying to grow fish in the pond, I wouldn't spend a lot of energy trying to force oxygen into water that doesn't want to hold it.

If your serious about avoiding eutrophication (the term for when water goes green and stinky), I would start with figuring out how to keep nutrients out of the water, they'd do you more good up on your land anyway. I think running water through a little wetland is a nice idea. The path through the wetland should be as long as you can make it, and it is better if the water runs through the soil rather than over the top. Wetlands produce good biomass that can serve you in other areas.

It sounds like there is kind of a tension between getting as much water as possible into the dam so you have some storage for the dry season vs. keeping the water, and nutrients, in the landscape where it can grow stuff. How critical is this dam to your water supply? I am kind of thinking that stepping back from 'fixing the dam' to looking at how you can manage nutrient and water flow across the site might give you some more satisfying answers.

Happy homesteading,

[9anda1f]

Excellent posts, Paul. Thank you, I learned a lot from your "system-of-systems" perspective!

9anda1f

[strud]

Paul,

You've made some great points there.

In the Sydney basin there is a serious water shortage at the moment (if you're on town water) but since we are on tanks & dam water (no mains connection) we need to be reasonably self sufficient unless we want to truck water in, which costs AU$95/13500L.

The real problem seem to begin at the start of the year when three months of rain didn't happen, ie dam got very low.

Second part of the problem occured (nutrient overload ?) probably since we bought the place in April this year. We don't have our dogs roaming the property since they are 'city' dogs and large Alaskan Malamutes. This in turn has caused the duck and other birdlife around the dam and paddocks to increase significantly I feel.

The only other possbile increase in nutrient supply would be a single horse in the same paddock as the dam, which is about 3 acres.

Maybe the dam was on the edge previously and the increase in birdlife has been enough to tip it over the edge ?

I have noticed a large amount of plant material (leaves and twigs etc) around the shallow areas in the dam and the bottom of the dam in these areas is a dark thick mud, probably great to add to the compost heap !

My plan of attack is as follows :

- Short term
- add barley straw to reduce algae load
- do some aeration to assist algae reduction

- Medium term
- remove excess nutrient from dam (introduce weed etc)
- prevent excess nutrient entering dam by building 'wetland' area in main runoff entrances

- Long term
- more trees (shade)
- dredge out sludge and add to garden etc

Sound OK ?

One last question, any suggestions for sourcing Barley straw in the Hwkesbusy area NSW ? Finding it a little hard to get.


a
ttempt to take some nutrient out of the dam

[Paul Cereghino]

Watch out... say nice things and I'll just keep blabbering...

- do some aeration to assist algae reduction

Hmm (im definately winging it here so put on your manure detector...)... Aeration will increase oxygen, oxygen will increase algal growth and capture of nitrogen into biomass, increase biomass will result in more organics to decompose that creates demand for oxygen... I'd say aeration will increase the rate at which you are turning nitrogen into algae but may not resolve your algae problem (which is why I imagine waste water treatment ponds do aerate.) I don't know if the effect justifies the energy input.

- remove excess nutrient from dam (introduce weed etc)

The path of least resistance in my mind would be to harvest the nutrients using emergent wetland plantings that you can cut and carry out of the system as mulch or forage. Our local cattail (Typha latifolia) is a wonder... the root starch is edible, the pollen is a flour supplement, the base of young shoots taste like cucumber, and the flowering stems make great mats). In this way harvesting nutrient rich biomass feeds into the revegetation of the wetland buffer creating a positive feedback loop.

- prevent excess nutrient entering dam by building 'wetland' area in main runoff entrances

Go out in the rainstorms and see where the water goes and base any runoff design on real world observations of water movement. Overland flow may be an issue... controlling your livestock access may be critical. During land development people flatten everything, and flat land doesn't function well.

- Long term
- more trees (shade)

This is one of the moist zones of your property, and given your regional water issues, I would milk as much yield out of that system as you can design. Look into aboriginal wetland use as well if you folks have any good ethnobotanical record down under. Wetlands are typically full of good stuff. Watch water level and how it responds to your kind of rain. Look for vegetation structure on natural pools and emulate.

- dredge out sludge and add to garden etc..

could be a good free source of organics and nutrients while gradually reducing N load in pond -- I just hate the thought of the labor :) It would be interesting to learn how to 'garden' the drawdown zone... When I was travelling in Laos everyone was growning their vegies in the moist flood sediments of the Mekong.

[strud]

It would be interesting to learn how to 'garden' the drawdown zone... When I was travelling in Laos everyone was growning their vegies in the moist flood sediments of the Mekong.



I saw this and thought I'd give it a go. Today I planted somw Sunflower, watermelon, rockmelon and zuchini in the nutrient rich 'drawdown' section of the dam. I'm assuming that the level isn't going to come up too soon (entering very dry stretch I think).

Figured that since the sunflowers have a deep tap root, they can chase down the water level as it dries out, whilst being moist enough in the early stages to get them going. Dont know how the others will go, not sure how deep their roots will go.

CS