Increasing rainfall infiltration from around 20% to almost 100% in a few years- looking for feedback

Hi Permies,

Looking for some feedback on an idea for a clay slope with around 80% runoff. This idea is for a clay slope with a dam around mid slope. A swale is attached to the mid slope dam and there is also another swale 4 metres lower in elevation from the dam.

Context - There is a short and intense wet season and a long dry season with about 7 months having almost no rain.  Every drop of rain is valuable in the dry season!
Rain overflows the mid slope dam multiple times over the wet season.  

Idea - Over the first 4 months of the wet season water is released from the mid slope dam down to 3 bunyip pumps which pump water to a higher water storage.  Bunyip pumps pump at 60% efficiency. The water released from the mid slope dam down to the bunyip pump leaves capacity for the next rain to fill the dam reducing overflow on the swales and giving time for water to be slowly released into the lower swale and have time to soak in.  The last month of the wet season pumping stops to ensure the mid slope dam is full to capacity.    

Please let me know if there are any problems with the concept or calculations.  I hope it is sound as it could transform this site or other similar sites very quickly. Note there are some variations in the specifications provided by the Bunyip pumps company. I have taken the average of their official specs and some correspondence they sent me. Please check out the links and attachments for details and calculations.

If correct this idea doubles water infiltration and pumps 10 + ML to 35 metres in the first year. It would be possible soak in all wet season rain within a few years with improved infiltration rates.  The current infiltration rate is only 2mm per hr.  

Diagram of the idea

https://docs.google.com/drawings/d/1YURWHcWVwxp_sotW6r-4dJ1phIAbUMXoFb8b_UaBUa8/edit

Refer to attachments for Bunyip pump specs.  

The dams are intended to be integrated with swale food forest and planned grazing like some of the features in this animation.  



Thanks for feedback!

Cheers,

Amanda  

Hi Amanda.  Interesting project!  The approximate degree or % of the slope would be useful to those who wish to help you.  As would the intended goal of the property besides infiltration.  Are you grazing, growing veggies, making an orchard?...   More than 15% slope and you could be causing trouble, especially with clay/high rainfall storms.  Calculate everything for worst-case scenarios, including the spillways on your swales.  Don't graze animals on dams.  Stabilize outer slope of dams with net rooted species.  Build dams proper with clay keys and compacted layers to withstand hydraulic pressure.  This is general info.  People can be more specific if they have more details of your plans.    

 ...80% is a lot of runoff, so it seems as though your clay is quickly swelling, sealing, and then the runoff occurs?  What plants, if any, are growing on your slopes?  A good thing to do would be to get a lot of roots penetrating that clay, as well as breaking up/interupting the overland flow.  As the permaculture gurus state, you want to slow, spread, and soak the water.  Your swales will do that, but so will every plant or cross-slope barrier in your land, and the deeper the roots, the better.  

Anyway, with more details of your plans for the land, and the slope itself, it'll be hard for other people to give you ideas.  

Great thinking though in contemplating swales and pumps for hydration.  I like the posted video.  

Hi Roberto,

Thanks for the feedback.

The average slope of the catchment is 6%.  The run off co-efficient is 0.82 .


Water infiltration is 2mm per hr into a tight clay soil.

Here is a link to the proof of concept design on the property I live on. https://docs.google.com/presentation/d/1MLq-wKSk-C58TYtlUatB_CewMT88FicPjAuj0i-zUFU/edit#slide=id.g40f2d82ba2_0_0


Good clay on the site.  There are several dams on the site. We have 10 cattle and a small hugel mound food forest in Far North Queensland Australia (20mx5m).


I'm not particularly interested in a detailed analysis of the whole design in the google slides. Just more in the bunyip pumps/swales over the wet season, feature.  With dams overflowing throughout the wet season, I figure why not look at the rainfall data averages and figure out how much water I could release to a lower swale, to soak in over time while also going through bunyip pumps and pumping to higher elevation for later gravity irrigation. On this site of 30.2 acres catchment I believe it would double the infiltration rate and pump 10.8 ML water to a 35 m elevation dam. With improved vegetation, planned grazing and trees on swales I think the infiltration rate could be easily improved from 2 mm per hr.  Instead of infiltration only occurring with rain events water it would be constantly released for 3 months into the lower swale. Then the mid slope dam has the reserve capacity to fill again with the next big rain. We have cyclones most years that dump a lot of water.
I would expect in 2 or 3 years almost 100% of the wet season could be soaked in and some of the 3 pumps could be used on other parts of the larger property with the same set up. Data and calculations are included in the pdf file.

Thanks for your feedback Roberto,

Cheers,

Amanda
   

Amanda your plan seems like a pretty solid one, I really like the idea of pumping the wet season water that would just run off back up slope to use later. Could you incorporate key line ripping above the top dam and possibly between the two dams to improve the infiltration?
The only thing that comes to mind for me is, if you dramatically improve your infiltration will the oumos become superfluous? And if so, what does the cost/benefit of the system look like? Could the result be achieved significantly cheaper without the pump?
At first blush though I love the idea

Sounds awesome.  It seems like your pump system would work out pretty well.  I don't have anything really to add to that.  I'm no engineer but your calculation seem about right.  I really like the idea of bunyip pumps!  

I also like the keyline ripping that S. Lowe mentioned.  Those could go a long way to increasing your upslope infiltration, as would a cross slope swale at the top of the property, if feasible.  

Another thing you could do with your system, is make part of the lower swale be a wider ditch, like a shallow pond, and grow something in it.  Because there will be a lot of nutrient in that last swale, and soon after that, you will be losing that nutrient off the downslope border of your property; so you could loop that back into the system before it is lost.  You can either use that ditch swale plot/plant-bed for a main crop, or you could mow it's biomass and haul it by cart up to mulch your food forest, to feed cattle, or to mulch other areas to further improve infiltration.  Move the plot's material as far upslope as possible in most cases as it then sends the nutrients back through the full system again.

I have heard vetiver suggested for infiltration. If it will grow, or if something will do its job of growing tall grasses and root zones of commensurate mass and length, I would plant it in on-contour rows. I definitely remember Geoff Lawton talking about the use of clumping bamboo plantings to slow surface water and to promote infiltration. I definitely remember him doing a video walk-through where he pointed out the bamboo, and how it looked barely touched by the flooding that had just occurred.

I would consider perhaps deepening any pond catchment as much as geophysics will allow. The deeper the pond, the colder the water, which means the greater the oxygen carrying capacity. Also, the greater the subsurface area where the slow, seeping infiltration through the clay layers might occur. I think I would make sure that all the existing dams had proper root mat coverage, but if the soil is clay throughout, and so if there is no danger of damaging a pond seal and releasing stored water to the aquifer (you're intending to increase infiltration anyways, right?) you could dredge with buckets over time to counteract sediment buildup, put said source of fertility to work for you in gardens or other plantings, and slowly increase your storage capacity, and therefore the length of time you'd be able to cycle that water over and through your land between rainy seasons.

Please send pictures if and when possible. Keep us posted, and I wish you the very best of luck.

-CK

Hi S.Lowe, Roberto and C.K,

Thanks for the feedback.

Keyline ripping would be difficult due to trees and tree stumps in the catchments. Im more inclined to use planned grazing to improve vegetation and trees on the swale mounds.

The point was made that infiltration will improve to the extent that bunyip pumps would become unnecessary.  Good point. I think I would go down to one pump from 3 pumps and start pumping months earlier resulting in the slower release of water. I would still like to have one pump pump working as I like the gravity irrigation water for later in the year. The 2 other pumps can then be used elsewhere on the larger site.

The initial reason for using 3 bunyip pumps was that the exhaust water released per hr was a little less than the swale could infiltrate per hr.  This means the site would be able to soak almost 100% of the rainfall in 2 or 3 years instead of without them which would be a much slower land improvement. That might take a decade and require a lot more time and capital to get the same result.

Good point about getting biomass back up the hill.  I think I would do this by having the cattle graze at the bottom of the hill and have their water points as high as possible so that their manure and nutrient comes back down.  Currently the site is pretty lifeless and unproductive so I am not worried about excessive nutrient.

I like your points about using pond fertility for garden. Water plants grow so fast and sediment also build-up fast! Currently there is room for improvement with the dam wall vegetation and the mid slope dam capacity could be expanded.

The main advantage I see with the bunyip pump swale set up is that it suits sites with poor agricultural soil (cheaper land). (Although too much rock or solid rock wouldn't work) In Australia these properties are called 'lifestyle' blocks.  For those who understand that topsoil can be created with the right management I think there is an opportunity to create a productive paradise in a few years for cheaper than good soil would be to buy.

Hopefully I will make some progress on this project and post some pics.
Thanks for the feedback,

Cheers,

Amanda      
 

Great!  Would love to see pics and maybe video of the whole thing in motiion!