Yeah, my picture is quite poor. I'll have to take a better one. There is not a 'swale' but a spot at the end of the front bed (mud) where the water collects. The downspout comes to the end of the column, and then a long extension goes out 5 or 6 feet towards the yard. At the end of the extension, water pools in my bed and pushes the dirt around. I don't like the extension--it's ugly and sticks out like a sore thumb Water will need to be directed away from the porch foundation. We have clay soil, which I've been amending slowly but surely, and it does stay wet there for quite some time after a rain. It's a west facing house, though, so during the summer it can get quite toasty there. Rain garden to me means a special garden made up of a range of plants--from water loving to moisture tolerating planted in a swale (usu. on the edge of slope below a downspout or a source of water). The rain garden helps to use the rainwater to keep it from entering storm drains, etc.

Actually, designing a swale or even a rain garden is a good idea for many gardens, even quite small ones. And it really doesn't make too much difference with the dryness - or not - of the climate. Unless already existing as a low lying, water accumulating area (i.e. a bog or swamp, perhaps only seasonally), a swale will simply catch and retain rainfall and allow it to be gradually absorbed into the soil. Among the reasons for this is to avoid seasonal flooding of the landscape, to reabsorb pollutants that are present in storm run-off before they can reach streams and groundwater or simply to retain and re-use infrequent rainfall. In your case, the latter seems most appropriate although when it does rain in SoCal, that rain can come fast and furious, so the other two reasons may be equally as valid as well, at least on a now-and-again basis. A swale is just a low lying area......when rainfall does occur, the water will flow to the lowest point, the swale, so it does need to be constructed to be lower than current grade. If any slope to the yard at all, the swale should be located at the low point. If not, you need to grade your new "lasagna" planting to slope away from the structure and toward to the designated swale site. And you will need to excavate the swale to some degree, depending on the thickness you can manage with your lasagna method. I doubt constructing swales was devised with a lasagna method of bed construction in mind. It does involve some work to do it correctly. Grading and directing water runoff to the correct area is critical. And you want something that slows water penetration yet provides good drainage at the bottom of the swale, not just soil - coarse sand and river rocks or coarse drainage gravel are common. And yes, this is much more of a landscape design issue than just a soil question ;-) Do some research online to see how to construct an effective swale. Even check out rain garden sites - they are a wealth of information for this sort of activity if for a slightly different purpose. One other thing you may want to do is investigate dry stream beds as a landscape feature. Not only do these make an attractive focal point to a drought tolerant garden, they will help to direct any rainwater runoff (even irrigation run-off) to the appropriate swale location where it can be dissipated evenly through the soil profile. Where moisture accumulates surrounding the swale and along its sides is where you can locate more thirsty plants. If you don't already have a landscape designer, you might want to consider hiring one. They could be a huge help in the layout, design and construction of this kind of feature, as well as offering suitable planting suggestions.

If I recall, you asked about plants for other areas of you sister's yard a year or two ago. If you have started her plantings, would you be willing to post some photos? Adding organic matter to the bed will help even out moisture as will mulch to make this a more successful garden. Here are some plants (some of which are natives so should be relatively easy) that are happy in a damp area. Many of these Dee mentioned, but here are comments based on my experience growing them. Shrubs: - Rhododendron viscosum (swamp azalea) has white to pink early summer flowers (just fading now) which are vanilla scented. This will only flower if it gets at least some sun. It gets some fall color also. Native - Clethra alnifolia (Sweet pepperbush or summersweet) has spikes of white to pink late summer flowers and clear yellow fall color. Some of the selections of the species are better than others for impact: Ruby Spice has pink flowers or Anne Bidwell sports clusters of white spikes or Sixteen Candles is compact with large white spikes. Flowers better in more sun, but tolerant of sun, shade, wet or dry. Some varieties will sucker. Native - Ilex verticillata (winterberry deciduous holly) has showstopping fall to early winter scarlet berries on bare branches, but needs at least half day sun to flower and berry well. Winter Red holds the berries the longest, according to research I've read and is the variety I grow, though only now getting large enough to berry. They may sucker some. Be sure to plant the appropriate male in an unobtrusive place in order to get berries. Native - High bush blueberries like some extra moisture, but not standing water, so could be planted in the less wet areas. Spring flowers, berries, fall color. Native - I think any of the shrubby dogwoods are pretty tolerant of wet feet and you can find them with various shades of red or gold twigs for winter interest as well as with variegated foliage. some native, some not, but all easy. Some will sucker. - There are various dwarf (4-12 feet rather than 30 feet) forms of Thuja occidentalis, eastern white cedar AKA arborvitae which grows in swamps if you want some evergreen interest. Deer like this if you have many of them . I haven't had any issues with them being eaten by deer. Native - Andromeda polifolia (bog rosemary) is a lovely low-growing evergreen, but can be fussy if it doesn't get even moisture and organic, acid soil. It is fine with part sun and has pink bells in spring and narrow, bluish foliage. Native - Ledum groenlandicum AKA Rhododendron groenlandicum (Laborador tea) is a low-growing plant with leathery leaves and clusters of small white flowers in spring. Native - Rosa palustris is a native wetland rose with single pink flowers in early summer and nice scent. The hips are decorative also. Native Perennials: - Caltha palustris (marsh marigold) has bright yellow spring flowers in wet areas, and the foliage will die back in summer if it's dry. It seems to do well in some shade since it grows and blooms largely before the trees leaf out. Native - Osmunda cinnamonea & O. clatoniana (cinnamon & interrupted ferns) both provide statuesque foliage for shade to part sun. They tolerate wet soil, but are happy if the soil is normal moisture also as long as it doesn't get both sunny and very dry. Native - Osmunda regalis (royal fern) is a tall lacy wetland fern with beautiful clear yellow fall foliage and requires wet soil all the time. Native - Veratrum viride (false hellebore) has large, pleated foliage that would make a good hosta substitute and needs to be in a wet area. Everywhere I know that this grows is in the shade. I've never seen it at a regular nursery, but you might find it at a wetland mitigation nursery or specialist nursery for wetland plants. Native - Camassia is a PNW native that likes moisture and has blue spring flowers. It can be purchased through good bulb suppliers like Brent and Becky's Bulbs www.brentandbeckysbulbs.com/ For late summer bloom, there are several large statuesque plants, including Eupatoriums and Veronias, but all need at least half day sun and are happiest in full sun. all native Eupatorium purpureum (now renamed by botanists as Eupatoriadelphus maculatus, common name joe pye weed) has clusters of mauvy purple fringy flowers in late summer. Eupatorium perfoliatum (boneset) has similar clusters of white flowers in August. Veronia has deeper purple flowers. Vernonia fasciculata (prairie ironweed) is tolerant of moist and dry conditions as is V. noveboracensis (New York ironweed.) - Iris versicolor (blueflag iris) is a native iris that I've seen blooming in full shade. It will bloom better in some sun. (As a side note, don't plant Iris pseudacorus, yellow flag, as it is an non-native that is invasive in wetlands.) Japanese and Siberian irises are happy with wet soil and will be fully hardy for you since I can grow them about an hour north of you. I'm not sure if Louisiana iris is hardy enough since I've seen various assessments of hardiness, but not grown them. - Lobelia cardinalis (cardinal flower) is a native that grows along streams and river banks, but will also grow in ordinary garden soil. I'd avoid Lobelia syphilitica (great blue lobelia) because IME it is a rampant self-seeder unless one always deadheads; ten or so years ago I removed them from by garden, but I am still finding volunteers in the garden, the lawn, the gravel drive, etc. - Clematis viriginiana grows along the steam on the floodplain in wet soil here, so should be fine for you. It will bloom less in less than full sun, but as long as it has more than 5 hours of sun should be fine. It has lots of tiny white flowers in late summer, sort of like sweet autumn clematis. - Clematis crispa is also native to swampy areas and has smaller bell-shaped flowers in shades of white and light lavender and mauve. - Clematis glaucophylla has pink and cream bells and also is native to lowlands along streams. Here is a site that will give you information about some of these native (though not all to NH) clematis: http://www.clematisviorna.info/ and here is a place that often carries some of these clematis http://www.gardenvines.com/. (You can request to be informed via email when they are back in stock since they are all currently out.) I tend to grow these small-flowered clematis near large shrubs so they can climb and ramble around whatever is nearby. They seem to play well with others as long as I let the shrubs get well-established first, so I tend to plant my clematis after the shrubs are 2 or 3 years old. They will also grow on a traditional obelisk or trellis. All want to get cut to about a foot sometime during the non-growing season, though they will do fine if not cut back, just will bloom higher on the plant. My favorite ground cover for average to wet garden soil and full shade to full sun is common cranberry, Vaccinium macrocarpon. It is another native, with tiny evergreen leaves, equally tiny pink flowers, and startlingly large red berries which persist until spring. It weaves well among other plants and never get taller than about 4 inches, though it may spread 2 or 3 feet in all directions, rooting as it spreads. It doesn't smother other plants, so it's a great groundcover to plant, though it will need mulch to prevent weeds coming up through it. It is denser in more sun.

Back to the real problem children. It is now accepted here in Australia and I am sure in some land management circles in NZ, that piping or concreting natural waterways creates significant environmental problems. This is now recognised in most developed countries. By concreting a waterway, the velocity and volume of the water is increased. I wo'nt go into the figures, but as communities expand, there is a incremental increase in the surface run-off of water. Imagine the inner city area of say Auckland. Most of the land area is now covered with buildings, roads, etc. so that nearly all the rainwater just runs off into the drainage system. The more the suburban fringe expands and the inner area gets built on, the larger the volume of water, that is prevented from soaking into the soil or just meandering through a catchment. But it all starts upstream, when the first house gets built and then the roads and so on, etc. etc. Back to the creek. When increased runoff hits a nice smooth concrete surface it gets faster and compounds to such an extent, that severe erosion and flooding now occurs down steam. This can be disastrous. In my landscaping lectures I recall seeing lots of photos of erosion and slippage etc. in New Zealand. Flooding is now tragically common in the lower suburban areas of the Sydney basin and I am told in parts of Wellington. It may well occur in other communities of New Zealand as well. As a result there are severe requirements on housing estates etc. to inhibit water runoff. Swales, detention basins(dams), wetlands to take out nutrients, etc.,are now mandatory. You will find this the same in America and Europe as well. For example, those big open concrete drains we see beside freeways that once were creeks are now being ripped up. Landscaping companies are being contracted to reinstall a sort of creekline that has curves etc to slow the water. Millions are being spent here, to recreate a sort of creekline with obstructions like rocks and even the broken concrete from the old open drain is being used. Vegetation is being reintroduced as it also slows down the water as well as helping to deal with erosion, take out nutrients, encourage habitat etc. What appear to be large parklands or football fields, are now detention basins designed to hold water run-off in severe downpours. Regarding your problem with the eels. This is an area where I know very little about. But I would suggest introducing more rocks of varying size so the holes are smaller between them. Is there a way to live with the eels and yet prevent them damaging the creekline. My bet is, if you put down a pipe you will add to a problem further down stream. A natural stream sounds like a great thing to have. Consider the cost piping the creekline and spend that budget on planting and improving the 'natural' look. Might I dare suggest you talk to a sandal 'wearer.' One of them might just be of help regarding the eels.